Collected Papers on 

Methods of Analysis 

for Uranium and 

Thorium

GEOLOGICAL SURVEY BULLETIN 1006

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

" ^.

Collected Papers on 

Methods of Analysis 

for Uranium and 

Thorium

Compiled by F. S. GRIMALDI, IRVING MAY, MARY H. FLETCHER, and JANE TITCOMB 

GEOLOGICAL SURVEY BULLET.IN 1006

This report concerns work done on behalf 

of the U. S. Atomic Energy Commission 

and is published with the permission of 

the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1954
3

UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. Price $1.00 (paper cover)
FOREWORD

The U. S. Geological Survey has made an extensive investigation 

of radioactive raw materials in the United States since 1945. This 

investigation was first undertaken on behalf of the Manhattan 

District Project and later on behalf of the U. S. Atomic Energy 

Commission. As a vital part of this program more than 200,000 

samples have been chemically analyzed for uranium. These samples 

included nearly all types of minerals, rocks, and ores; mill, smelter, 

refinery, and other plant products; and natural waters.

From the start of the program it was evident in the Geological 

Survey and elsewhere that the existing methods of uranium analysis 

were inadequate, and therefore much work has been done in modifying known techniques and developing new ones. The first stage of 

this work was based on classical techniques; the second stage led to 

the development of more rapid methods to meet the constantly 

expanding analytical load. Work is continuing along both lines.

What has been said about uranium analysis applies equally to 

thorium analysis. No satisfactorily rapid analytical methods for 

the chemical determination of thorium, especially for very small 

amounts (less than 1 percent), have been developed. The demand for 

thorium analyses is always pressing in the Survey program, and 

research in this field has been and is intense.

The analytical methods developed from these investigations have 

been reported from time to time in U. S. Geological Survey Trace 

Elements Investigations and Memorandum reports, and many of 

these have been reproduced by the Technical Information Service 

of the Atomic Energy Commission at Oak Ridge, Term. These 

reports have had limited distribution in the Geological Survey and 

to the Atomic Energy Commission and its contractors, but it is 

desirable to make them available for wider distribution through 

formal publication. This bulletin will serve that purpose.

The methods herein described include standard ones as well as those 

requiring the use of rather elaborate and highly specialized instruments. The primary goal has been to develop methods that are of 

the widest applicability, and some procedures may be unnecessarily 

long when applied to simple materials.

The papers are presented in nearly chronologic order and thus 

reflect the changing demands on the laboratory. The reports have 

been kept essentially in their original form except where it has been 

necessary to bring the material up to date. Some of the earlier 

methods have, been superseded by those described in later reports;

in
IV FOREWORD

nevertheless, they are presented here because the information they 

contain is valuable and useful.

The authors who compiled this bulletin have prepared a general 

discussion (part 1) of uranium and thorium analysis that will be most 

useful to those working in this field.

JOHN C. RABBITT, 

Chief, Trace Elements Section.
CONTENTS

Page

PART 1. Summary of methods of analysis for the determination of 

uranium and thorium, by F. S. Grimaldi, Irving May, M. H. 

Fletcher, and Jane Titcomb._____________________________ 1

2. Methods for the complete decomposition of rock and ore samples 

to be analyzed for very small amounts of uranium and thorium, 

by M. D. Foster, R. E. Stevens, F. S. Grimaldi, W. G. Schlecht, 

and Michael Fleischer___________________________________ 11

3. The Geological Survey cupferron precipitation-extraction method 

for the determination of very small amounts of uranium in 

naturally occurring materials, by F. S. Grimaldi-___________ 17

4. The Geological Survey carbonate-phosphate-peroxide method for 

the determination of very small amounts of uranium in naturally occurring materials, by M. D. Foster and R. E. Stevens.. 29

5. Elimination of interference by nickel in the determination of 

uranium by means of zinc amalgam reductors, by F. S. Grimaldi_______________________.--------._---._-_-___ 37

6. The visual fluorimetric determination of uranium in low-grade

ores, by F. S. Grimaldi and Harry Levine____-_---________- 43

7. A volumetric filtering pipette, by F. S. Grimaldi-_____________ 49

8. A study of critical factors in the "direct" fluorimetric determination of uranium by Mary H. Fletcher___________________ 51

9. A direct fluorimetric method for the determination of small 

amounts of uranium in the field and laboratory, by F. S. 

Grimaldi, F. N. Ward, and Ruth Kreher Fuyat. _ _____ 69

10. An improved fluorimeter for the determination of uranium in

fluoride melts, by Mary H. Fletcher and Irving May__-____- 77

11. A transmission fluorimeter for use in the fluorimetric method of 

analysis for uranium, by Mary H. Fletcher, Irving May, and 

Morris Slavin___---____---__---__-_----__----___-_-____ 85

12. The design of the Model V transmission fluorimeter by Mary H.

Fletcher, Irving May, and J. W. Anderson_________________ 93

13. A battery-powered fluorimeter for the determination of uranium,

by Irving May and Mary H. Fletcher____________,_________ 97

14. Short routine direct method for the fluorimetric determination of 

uranium in phosphate rocks, by F. S. Grimaldi and Norma S. 

Guttag._________-_-____--_--_------_-._------_-_- _. 105

15. Fluorimetric determination of uranium in shales, lignites, and 

rnonazites after alkali carbonate separation, by Norma S. 

Guttag and F. S. Grimaldi--________-__________ 111

16. Noninterference of arsenate ion in the volumetric determination

of uranium using the Jones reductor, by Jack J. Rowe______ 121

17. The fluorimetric determination of uranium in nonsaline and

saline waters, by Audrey Pietsch Smith and F. S. Grimaldi-_ 125

18. The Geological Survey phosphate-fluoride-iodate method for the 

determination of very small amounts of thorium in naturally 

occurring materials, by F. S. Grimaldi and J. G. Fairchild___ 133

V
VI CONTENTS

Page

PART 19. The Geological Survey carbonate-iodate-iodine method for the 

determination of small amounts of thorium in naturally occurring materials, by J. J. Fahey and M. D. Foster.___________ 153

20. The determination of thorium in high-grade and low-grade ores,

by F. S. Grimaldi and Charlotte Marsh Warshaw___________ 169

21. Mesityl oxide extraction method for thorium analysis, by Harry

Levine and F. S. Grimaldi _ _____________________________ 177

ILLUSTRATIONS

[Plates 3-8 in pocket]

Page 

PLATE 1. Assembly of Model II transmission fluorimeter______________ 62

2. Model II transmission fluorimeter__-______________-_______ 63

3. Rear-view assembly and expanded details of the modified 

fluorimeter.

4. Fluorimeter assembly.

5. Cutaway view, cross section, and details of parts of "fluorimeter".

6. Details of parts of fluorimeter assembly shown in plate 4.

7. Details for construction of shield.

8. Details for construction of type-B phototube housing. 

FIGURE 1. Volumetric filtering pipette._______________-______------__ 50

2. Details of volumetric filtering pipette______________________ 50

3. Effect of fusion conditions on fluorescence of blank samples. _ _ 57

4. Effect of fusion conditions on fluorescence of standard samples. 57

5. Effect of fusion conditions on sensitivity..---.______________ 58

6. Equipment--_-_____-___________--______--___-_-__-____- 62

7. Effect of fusion conditions on fluorescence of standard samples

as shown in new data__________________________________ 66

8. Effect of fusion time and type of platinumware on fluorescence

of standard samples.-.-----------.--------------------- 68

9. Complete assembly of the modified fluorimeter______________ 79

10. Standardization curves for 3.0-g discs prepared by fusion in

30-mlcrucibles_______________________-_____________.__ 80

11. Standardization curves for 1.5-g discs prepared by fusion in

crucible lids.____-_______--_------------------------- 81

12. Calibration curves for routine work.__._____-______-.___.__ 83

13. Schematic diagram of a "reflection"-type fluorimeter_________ 86

14. Schematic diagram Of a transmission-type fluorimeter________ 87

15. Lamp circuit used in the instrument-______________________ yy

16. Reflecting support for the lam.p_______________ ____________ 101

17. Power circuit for the photomultiplier tube_.________________ 101

18. Standard CUrV6..______. ._ . - 102

19. Platinum dish used for fusions.-..----------.-------------- 103

20. Working curve_-_.__________________--------_---_-__ 109

21. Spectral transmittancy curve for the determination of thorium

with p-dimethylaminoazophenylarsonic acid________._...-- 150
CONTENTS VII

FIGURE 22. Fisher electrophotometer readings for the photometric determination of thorium with p-dimethylaminoazophenylarsonic acid___-_________-_-_-_______--_--_-----__--_-__ 151

23. Spectral transmittancy curve of iodine in carbon tetrachloride. 164

24. Transmittance-concentration curves of iodine in carbon tetrachloride -___-__________------__-___--_--_____---______ 165

25. Spectral transmittancy curves of iodine in carbon tetrachloride, methyl red in acid solution, thymol blue in acid 

solution._______._____________________________________ 197

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 1. SUMMARY OF METHODS OF ANALYSIS FOR THE 

DETERMINATION OF URANIUM AND THORIUM

By F. S. GRIMALDI, IRVING MAY, M. H. FLETCHER, AND JANE TITCOMB

CONTENTS

Page

Uranium analysis_________________________________________________ 1

Fluorimetric methods__________________________________________ 2

Direct or "dilution" method_____________.__________________ 3

Extraction method_______________________________________ 4

Carbonate method.._______________________________________ 5

Accuracy of fluorimetric methods _-----_-----___-____---__ 5

Colorimetric methods______________.__-_-_____.__.____._.._____ 6

Thorium analysis.______________________-___-----___.________-_-_ 7

Methods of separation_..___________.__-_-_-____.._______-___ 7

Separation based on precipitation of thorium orthophosphate. 7

Separation of thorium from the rare earths.....__.____________ 8

Separation based on the extraction of thorium nitrate with

mesityl oxide__________________________________________ 8

Separation of thorium from the titanium-zirconium and R20s

group __________________________________________________ 8

Methods of determination_____..-_____-_-_-_________-_----_---__ 9

Gravimetric_ ____________________________________________ 9

Colorimetric _____________________ _ _______________________ 9

Nephelometric-_____________ ___________________________ 9

CHART 

Quenching data on elements for 2 grams of flux__________________ 3

URANIUM ANALYSIS

Fluorimetric, colorimetnc, and polarographic methods are commonly used for the determination of small amounts of uranium. The 

fluorimetric method based on the fluorescence of uranium in fluoride 

phosphors is one of the most sensitive for the determination of uranium; 10~10 g of uranium is detectable. The lower limit of detection 

for most of the Colorimetric and polarographic techniques is about 

10~6 g of uranium. Although all methods can be used for larger 

amounts, a convenient upper limit for the fluorimetric determination 

may be set at 10~6 g, and for Colorimetric and polarographic determinations at 10~2 g of uranium.
2 METHODS OF ANALYSIS, URANIUM AND THORIUM

PLUOBIMETBIC METHODS

Melts obtained by fusing uranium salts with sodium fluoride fluoresce a brilliant yellow green when exposed to ultraviolet light. l The 

intensity of the fluorescence is proportional, within wide limits, to 

the amount of uranium present, and this relationship is the basis for 

the quantitative fluorimetric determination of uranium.

The fluorescence test for uranium is specific when the excitation is 

with long wavelength (3650A) ultraviolet light. Niobium fluoresces 

only weakly when exposed to short wavelength light (2536A). In 

spite of this specificity, many elements may interfere by quenching 

the uranium fluorescence. For example, a few micrograms of cobalt, 

chromium, nickel, or -manganese will reduce the fluorescence of uranium by more than 10 percent.

The uranium fluorescence may be enhanced by minute amounts of 

other elements that by themselves do not fluoresce in fluoride phosphors. This effect is seldom encountered in practice. Jacobs 2 has 

shown that this enhancement is frequently instrumental and is due 

to a shift in the spectrum of the emitted light to a region generating 

a greater response from the phototube. Depending upon the particular combination of filters and phototube used, this shift in the 

spectrum may appear as enhancement or quenching. In some cases 

the opposing effect of increased phototube sensitivity and decreased 

transmission by the filter will be .balanced, and no change will be 

apparent.

Two techniques are used commonly to reduce or to eliminate interference due to quenching. One tecloniqvie, called tlie "filiation"

method (or direct method) involves no chemical separations. It originated with Price 3 who found that it is possible to reduce quenching

to a negligible factor by using sufficiently small samples for analysis.

The degree of quenching depends only on the concentration of

quencher in the flux, and not on the ratio of concentration of quencher 

to concentration of uranium.

In the second technique the uranium is separated from quenching

elements before the fluoride phosphor is prepared, In one type of 

procedure uranium may be freed from quenching elements by precipitating them with alkali carbonate solution; the uranium remains in

solution as a complex carbonate. Alternately, the separation may

be accomplished by extraction of uranyl nitrate by organic solvents.

Tke latter procedure is also very Useful for the Concentration Of

uranium,

1 Nichols, E. L., and Slattery, M. K., 1926, Uranium as an activator: Optical Soc. America Jour., v* 14, 

P. 449.

2 Jacobs, S., 1950, A study of the determination of uranium by measurement of fluorescence: CRL/AE 52, 

Department of Scientific and Industrial Research, Teddington, Middlesex.

» Price, O. E., Ferretti, F. J., and Schwartz, S., 1945. The microfluorimetric determination of uranium: 

AECD 2282.
SUMMARY OF METHODS 3 

DIRECT OR "DILUTION" METHOD

The direct fluorimetric method consists of taking a small aliquot 

of an acid solution of the sample, evaporating it in a standard platinum 

or gold container, adding the fluoride flux, and preparing the phosphor 

by fusing at a low temperature. The fluorescence of the melt is then 

measured in a fluorimeter.

The size of the aliquot in the direct method depends on the composition of the material to be analyzed. This size may range from 

a few micrograms of sample (for materials containing strong quenchers 

such as chromium or manganese) to a few milligrams (for materials 

with low concentration of quenchers and/or containing relatively 

mild quenchers). The accompanying chart summarizes the magnitude 

of quenching produced by various elements. In general a 0.1-mg 

sample results in negligible quenching for most rocks; for some materials (phosphate rocks) several milligrams usually yields little or no 

quenching. It is preferable to use the maximum weight that results 

in no serious quenching in order that the level of fluorescence to be 

measured is considerably above that introduced by background 

contamination. If many samples of about the same composition 

are to be analyzed, it is advantageous to determine the maximum 

weight that can be used in the direct method. The measurement 

of very low fluorescence intensity levels requires the use of sensitive 

fluorimeters.

Quenching data on elements for 2 grams of flux

Be

Sc [Ti] ° [Or Mn| JFcj [Co Ni| i% Cu"~Znj Oa Qe ° Se

0 ° Nb* Mo Tc .Ru Rh Pd [Zg] Cd In [Snj Sb Te

[La] Hf Ta |w] Re Os Ir |Pt Au] Eg** Tl |Pb] Bi Po

Ra Ac JTh] Pa

|Ce Pr Nd] ° ° Eu ° Tb Dy Ho Er Tm Yb Lu

Heavy solid lines enclose elements that are strong quenchers (l-lO-y quench uranium fluorescence by 10 

percent or more).

Heavy dotted lines enclose elements that are moderate quenchers (10-507 quench fluorescence about 10 

percent).

Light solid lines enclose elements that are weak quenchers (50-1,OOOy quench fluorescence by about 10 

percent).

For elements shown but not enclosed there are no data. The transition elements are probably moderate 

to strong quenchers. Elements not shown do not quench the uranium fluorescence.

 Niobium fluoresces only with short-wave excitation (2536A).

"Mercury has been reported as a strong quencher of uranium fluorescence, but it is volatilized in the 

preparation of the melt.

EXTRACTION METHOD

In this method the uranium is separated from quenchers before 

preparation of the fluoride phosphor. This separation usually in-
4 METHODS OF ANALYSIS, URANIUM AND THORIUM

volves the extraction by means of organic solvents of uranyl nitrate 

from nitric acid solution after the addition of a salting agent. A 

portion of the solvent is then transferred to the standard container 

and after evaporation of the solvent, the phosphor is prepared.

The Geological Survey procedure (part 6) uses batch extraction 

with aluminum nitrate as the salting agent and ethyl acetate as the 

solvent. Aluminum nitrate serves also to complex F~, POi", and SO*" 

ions that otherwise seriously, hinder the extraction of uranium. Aluminum nitrate is also advantageous because any aluminum extracted 

does not quench the uranium fluorescence. Vanadium and quadrivalent cerium, thorium, and zirconium are partly extracted. Neither 

vanadium nor zirconium quenches the uranium fluorescence significantly, but cerium or thorium quenching may be serious. Interference 

due to cerium is eliminated when necessary by reducing the cerium 

to the trivalent state before extraction. With large concentrations of 

cerium, it is usually necessary to repeat the extraction. Because larger 

samples may be used with the extraction-fluorimetric procedure, less 

sensitive fluorimeters may be used; errors due to contamination are 

less serious.

The extraction of uranium by ethyl acetate may be made from 

solutions at acidities ranging from slightly acid to 20 percent by 

volume nitric acid. Depending on the acidity of the solution before 

extraction, the volume of the ethyl acetate layer may decrease or 

increase after extraction. Thus with slightly acid solutions the volume 

of the ethyl acetate layer decreases by 3 percent; with 15 percent by 

volume nitric acid, there is a 3 percent increase. In the range 6}£ to

1% percent nitric acid there is no significant volume change. Corrections for volume changes may be made by basing the working curve 

on extracted standards. Although the extraction procedures given

in this bulletin are based on extraction from (15-1-85) nitric acid

solutions, our present practice is to use (7 + 93) nitric acid solutions.

CARBONATE METHOD

In this procedure (part 15) an aliquot of a sulfuric acid solution of

the sample representing 15 mg or less is treated with alkali carbonate 

solution in excess to precipitate quenching elements; the uranium

mains in solution. After filtration, an aliquot of flic filtered wlutiw

is transferred to a standard container, the solution is evaporated, and

tfco strmcia/r<i MicJ/fc is jpn-eiia.i-ecl as tefore. Cerium, oobn.lt, and COpper

may interfere in this procedure. A very small amount of cerium and

cobalt follow uranium because the precipitates formed from sulfate 

solutions tend to pass through the filter. Most materials do not contain sufficient cerium to interfere, Witn suitable modification me

procedure may be used even for the determination of uranium in 

monazite. Cobalt is quantitatively removed when an element other
SUMMARY OF METHODS 5

than cobalt is precipitated with alkali carbonate. Copper may remain 

completely in solution yielding an intense blue solution. If the amount 

of copper not precipitated is insufficient to yield a blue solution, no 

quenching of the uranium fluorescence results. When a blue solution 

is obtained, a small amount of hydroxylamine is added after the 

alkali carbonate to precipitate cuprous oxide and thus remove the 

interference of this element.

The carbonate procedure does not accommodate more than 15 mg 

of various metal oxides and should not be extended without testing 

to determine that no occlusion of uranium occurs in the carbonate 

precipitate for greater quantities of metal oxides.

ACCURACY OF FLUORIMETRIC METHODS

With careful work uranium may be determined by the fluorescence 

method with no greater error than ±4 percent of the uranium content. 

Under routine conditions, where speed may be important, the error 

generally is greater and may range from ±8 to 15 percent of the 

uranium content. When errors occur the results are generally low.

COLORIMETRIC METHODS

Reagents. Various reagents have been used for the colorimetric 

determination of uranium. The most important of these are hydrogen 

peroxide (both in alkaline and slightly acid solution), ammonium 

thiocyanate, and ascorbic acid. The Geological Survey has adopted 

the alkaline peroxide colorimetric method. This procedure (part 3) 

is applicable generally and useful for the range 5X10~6 g to 2X10~2g 

uranium.

In the alkaline-peroxide procedure provision must be made not 

only to remove elements that precipitate in sodium hydroxide solution, 

but also to remove vanadium, chromium, and molybdenum that give 

yellow solutions similar to that given by uranium. Two separation 

procedures are in current use. The first depends on the extraction 

of uranyl nitrate as previously described, and the second uses cupferron for the separations. As a little vanadium accompanies uranium 

in the extraction procedure, it may be removed by cupferron before 

the colorimetric estimation of uranium, or the vanadium color may be 

destroyed by heating the alkaline peroxide solution.4 The cupferron 

separations consist of first reducing the uranium in a Jones reductor 

and precipitating the reduced uranium with cupferron. Usually the 

sample solution contains sufficient titanium to act as a carrier for 

the uranium. If no elements that precipitate with cupferron in 

acid solution are present in the solution, a few milligrams of titanium

4 Ooldbeck, O. O., and others, 1946, Colorimetric determinations of uranium by means of peroxide: Nat. 

Bur. Standards Rept. A-1074.
6 METHODS OF ANALYSIS, URANIUM AND THORIUM

are added as a carrier. The cupferron separates uranium from the 

major constituents and from chromium. The cupferron precipitate 

is ignited and dissolved; uranium is oxidized to the sexivalent state 

and then separated from elements that are precipitated with cupferron in acid solution by extracting the cupferrates of these elements 

with ethyl acetate. Uranium remains in the water layer. The 

uranium then is determined colorimetrically with hydrogen 

peroxide in sodium hydroxide solution, the hydroxide serving the 

additional function of precipitating the very small amounts of rare 

earths that may accompany uranium in these separations. A little 

chromium tends to follow uranium in the cupferron separations when 

the chromium content of the solution is high. Chromium is eliminated 

when necessary by repeating the reduction step.

Instruments. The colorimetric estimation may be made visually 

by comparing samples with a series of standards in Nessler tubes. 

These standards are made to contain amounts of uranium differing by 

0.1 mg in a total volume of 50 ml.

Measurements may be made with filter photometers using Corning 

filter no. 5543 but the sensitivity is appreciably lower than with a 

spectrophotometer. The Geological Survey uses the Beckman 

spectrophotometer; transmittancy measurements are made at 400 m/z. 

With a 0.1-mm slit, 1-cm light path, and water as the reference solution, 

an optical density of about 0.9 is obtained for solutions of concentration 0.2 mg of uranium per milliliter. With the Beckman spectrophotometer a precision of ± 1 percent of the uranium content may be 

obtained.

THORIUM ANALYSIS

Chemical methods for the determination of thorium are complex, 

IQVOlve difficult and tedioUB manipulation, and require the services

of thoroughly experienced analysts. The analytical chemistry of 

thorium is complicated by the colorless nature of the ion, by its single 

valence state, by the lack of selective and sensitive reagents, by the 

refrftCtOry nature Of its oresj and by its association with elements that 

present difficult analytical problems.

In most thorium analyses, provisions must be made for the separation of thorium not only from elements commonly determined in

rock and mineral analyses, but also from the rare ©artks, from tk©

dLadrVvrnlent elements, and from the quinquivalent elements such aS 

tantalum, There are many procedures ror tno Bt>piwrtvvj.w

from the rare earths, but only two procedures are COmmOnly 

used for the separation of thorium from the titanium-zirconium
SUMMARY OF METHODS 7

METHODS OF SEPARATION 

SEPARATION BASED ON PRECIPITATION OF THORIUM ORTHOPHOSPHATE

With zirconium as a carrier, thorium is precipitated quantitatively 

as the phosphate from solutions 2% percent by volume in hydrochloric acid (0.3N) and containing 2 g diammonium phosphate per 

100 ml of solution (part 18). This precipitation reaction separates 

thorium from most of the major constituents of rock samples and is a 

useful concentration procedure for trace analysis. In addition to 

titanium and zirconium, some rare-earth phosphates are also 

precipitated.

SEPARATION OF THORIUM FROM THE RARE EARTHS

With ammonium hydroxide. Thorium is separated from calcium, 

magnesium, manganese, and most of the rare earths by ammonium 

hydroxide precipitations at controlled acidity (part 20). At a pTH 

corresponding to the neutral color of methyl red, thorium is precipitated quantitatively, whereas most of the trivalent cerium and 

the other rare earths remain in solution. Either nitrate or chloride 

solutions of thorium may be used, but the sulfate ion must be absent. 

If much sulfate is present, considerable losses of thorium result at the 

methyl red end point, although precipitation of thorium is complete 

when excess ammonia is used. Sulfate may be removed by preliminary precipitations of thorium with sodium hydroxide.

Complete separation of thorium from the rare earths is not obtained in this separation, as the last few milligrams of rare earths are 

retained persistently by the thorium precipitate. The separation, 

however, is simple and exceedingly useful for removing most of the 

rare earths. Zirconium and titanium are not separated.

With potassium iodate. The separation of thorium from the rare 

earths by precipitation as the iodate is one of the best procedures. 

For macro amounts the reaction is carried out in 6N nitric acid solution. For quantities less than a few milligrams the final acidity of 

the solution (after all reagents are added) should not exceed IN 

nitric acid because loss of thorium results at higher acid concentrations (part 18). Two precipitations of thorium iodate from 6N nitric 

acid solutions are usually sufficient for separating the rare earths; four 

or five precipitations may be necessary at the low acidities. Cerium"1"4 , 

zirconium, and titanium also are precipitated by iodate. Cerium"1"* 

may be reduced by hydrogen peroxide to cerium4" 3 . More elements 

tend to coprecipitate with thorium iodate at low acidity than at high 

acidity. As the range of thorium content of most of the samples to 

be analyzed is unknown, we have standardized on low acidity for
8 METHODS OF ANALYSIS, URANIUM AND THORIUM

iodate precipitation because it is sounder. At high acidities the precipitation of thorium iodate is made by adding 50 ml of nitric acid 

and 100 ml of 15 percent solution of potassium iodate in (1 + 1) 

nitric acid to 100 ml of slightly acid solution of the sample. For low 

acidities 3 ml of nitric acid and 8 ml of 1% percent water solution of 

potassium iodate are added to the slightly acid solution of the sample, 

and the total volume of the solution is made to 50 ml by the addition 

of water. Thorium iodate may be dissolved by reducing acids, such 

as hydrochloric acid, and also by concentrated nitric acid.

With hydrogen peroxide. Thorium is precipitated by hydrogen 

peroxide as the peroxynitrate from solutions 0.03N in nitric acid or 

less. The concentration of hydrogen peroxide used is 5 ml of 30 

percent hydrogen peroxide per 100 ml of solution. The method 

adopted by the Geological Survey (part 20) uses 0.03N nitric acid 

because fewer elements are precipitated at this higher acidity. The 

precipitation of thorium with hydrogen peroxide is somewhat sensitive to changes in conditions of precipitation. Zirconium causes low 

recovery of thorium and must be removed completely before applying 

the peroxynitrate precipitation. Very slight losses of thorium (about 

1 mg or less of thorium oxide) occur in the presence of the sulfate ion.

SEPARATIONS BASED ON THE EXTRACTION OF THORIUM NITRATE WITH

MESITYLi OXIDE

Thorium nitrate is quantitatively extracted by mesityl oxide from 

solutions 2.5M in aluminum nitrate and 1.2M in nitric acid (part 21). 

The concentration of nitric acid is not critical and may range from 

5 to 30 percent by volume. The extraction is a batch extraction. 

All of the uranium is extracted quantitatively, most of the zirconium

and some of the rare earths and vanadium. The rare earths file 

stripped from the mesityl oxide by several washings with a solution 

2.5M In aluminum nitrate and 1.2M in nitric acid. Thorium is

stripped from the mesityl oxide by water after removal of the rare

earths. The mesityl oxide separation is also a useful means of concentrating trace quantities of thorium and may be applied in the 

presence of phosphate and arsenate. The mesityl oxide separation

is especially important for the Separation of l&TgG aHlOUntS Of

ftlld frOIfl Small amounts Of rare earths because precipitati 

do not yield as clean a separation for SUcll ft

cxrsr OF TEtonrrrM PROM THE TITANIUM-ZIRCONIUM AND BjOj

With oxalic acid. The separation of-thorium by precipitation as 

the oxalate is a standard method and is widely used. The advantage
SUMMARY OF METHODS 9

of oxalic acid over hydrofluoric acid for the same separation is that 

the thorium oxalate may be ignited and then weighed as the oxide. 

As the precipitant, 4 g of oxalic acid per 100 ml of solution are used, 

and the acidity of .the solution may be as high as 4 percent by volume 

of mineral acid. The rare earths accompany thorium. The solubility 

of thorium oxalate is such that for traces of thorium (less than a few 

milligrams) precipitation as the oxalate is not always applicable.

With hydrofluoric acid. Hydrofluoric acid provides approximately 

the same separations as oxalic acid. We prefer hydrofluoric to oxalic 

acid for these separations because the former is more consistent and 

reliable and also because it must be used when small amounts of 

thorium are to be precipitated. In the presence of alkalies and alkaline 

earths the precipitates from hydrofluoric and oxalic acid tend to 

occlude zirconium and titanium.

METHODS OF DETERMINATION

These methods presuppose that all interferences have been eliminated in the initial stages of the analysis.

GRAVIMETRIC

Thorium hydroxide, thorium peroxynitrate, and thorium oxalate 

are ignited to thorium dioxide which is weighed.

COLORIMETRIC

Few useful colorimetric methods exist for the determination of 

thorium because of lack of selectivity. ^-Dimethylaminoazophenylarsonic acid (pararsonic acid) is used at the Geological Survey (part 

18) for microgram amounts. Thorium is precipitated with the dye 

from buffered acetate solution, and the thorium precipitate is filtered 

and washed with the acetate buffer. The precipitate is decomposed 

with sodium hydroxide solution, and the density of the released dye 

solution is measured with a spectrophotometer.

An iodine liberation method (part 19) is also used in the Geological 

Survey laboratory and depends on the reduction of thorium iodate 

by hypophosphorus acid in the presence of sulfuric acid. The 

iodine liberated is dissolved in carbon tetrachloride and imparts a 

bluish-red color to the carbon tetrachloride.

NEPHELOMETRIC

Thorium, in less than 1-mg amounts, may be estimated nephelometrically as thorium iodate (part 18). The thorium is precipitated 

from normal nitric acid solutions with potassium iodate. The resulting turbidity is compared with a series of standards.

268681 54 2

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 2. METHODS FOR THE COMPLETE DECOMPOSITION 

OF ROCK AND ORE SAMPLES TO BE ANALYZED FOR 

VERY SMALL AMOUNTS OF URANIUM AND THORIUM

By M. D. FOSTER, R. E. STEVENS, F. S. GRIMALDI, W. G. SCHLECT, 

AND MICHAEL FLEISCHER

CONTENTS

Introduction ______________________________________________________ 11

General procedure _________________________________________________ 13

Nonocclusion of uranium by hydrolytic precipitates...-.______ _________ 14

TABLE

TABLE 1. Experiments showing nonocclusion of uranium by hydrolytic

precipitates.____________________________________________________ 15

INTRODUCTION

This paper presents the methods used for the decomposition of 

samples to be analyzed for very small amounts of uranium and thorium. It is desirable to have a general method applicable without 

modification to most types of rocks and ores, although some samples 

will require special treatment. Unless it is known otherwise, complete 

decomposition of the sample is essential, as uranium and thorium 

may be present in some of the most refractory minerals such as 

zircon, microlite, and monazite. The procedures presented in this 

report are based on experience gained from the analyses of hundreds 

of samples over a period of more than 2 years.

The general procedure given below is satisfactory for most types of 

rocks and ores, whether siliceous or phosphatic. It is not satisfactory 

for samples, such as placer concentrates, that contain large amounts of 

very refractory minerals; a special procedure is given for these samples.

To determine traces of uranium and thorium, large samples may 

have to be decomposed; the procedure is designed to avoid introduction of large quantities of alkali salts. The samples are decomposed 

by means of volatile acids wherever possible; nitric and hydrofluoric

NOTE. This report was issued as Trace Elements Inv. Eept. 31A and AECD 1782,1946.

11
12 METHODS OF ANALYSIS, URANIUM AND THORIUM

acids are used for the initial treatment. The hydrofluoric acid is 

removed by repeated evaporations with nitric acid, which is then 

removed by evaporations with hydrochloric acid. This is a slow 

procedure, but requires little attention by the analyst, and many 

samples can be handled simultaneously. If desired, the hydrofluoric 

acid may be removed more rapidly by fuming in sulfuric or perchloric 

acid. However, the use of sulfuric acid is undesirable for several 

reasons. Many samples, such as phosphate rock and limestone, have 

high calcium contents and most of the calcium precipitates as sulfate. 

In one of the procedures for the determination of thorium (part 18), 

the insoluble calcium sulfate will accompany thorium, and the separations of thorium from zirconium and titanium using hydrofluoric 

acid or oxalic acid may fail because of the formation of insoluble 

salts such as calcium zirconium fluoride and calcium zirconium 

oxalate. Furthermore, the presence of the sulfate ion ties up thorium 

as a complex anion and interferes with many precipitation reactions 

of thorium. For instance sulfate may interfere in the precipitation 

of thorium with iodate, with ammonia; and with peroxide.

Perchloric acid is avoided because the presence of perchlorates 

may lead to the formation of rather stable emulsions during the 

extractions with organic solvents (such as ethyl acetate) in the 

analytical procedures.

The attack with volatile acids generally decomposes most rock 

samples. If a little unattacked residue remains, it is generally brought 

into solution by sintering or fusing with a minimum of sodium

carbonate.

Elements such as niobium, tantalum, titanium, zirconium, thorium, 

tin, tungsten, and antimony may form hydrolytic precipitates, especially in the presence of phosphate. Such precipitates do not

occlude uranium (table 1) and may be filtered off and rejected if only 

uranium is to be determined, but must be reserved if thorium IS to

be determined.

Modifications Of the general procedure are desirable for certain 

unusual samples, and judgment must be eXeiClSed bj the analyst. 

TWO examples Will illustrate. Samples very high in iron oxide are

best digested first in porcelain With (l + l) hydrochloric acid, filtered,

and Washed With hot water. The filtrate is reserved. The inSOlublC

residue is ignited in platinum then treated as in the general procedure

Starting With Step 3. The reserved filtrate is ad<ioa a.ftor the

stride has been removed. Samples containing much fluorite

(CaF2) are not decomposed readily either by concentrated nitric acid 

Of COnCOnt/Iirte<1 kjfdrochloric acid. They may be fumed With P6I" 

chloric acid, or better, evaporated iwice With1 (11"2) hju
METHODS FOR DECOMPOSITION OF ROCK AND ORE SAMPLES 13

Special procedures are used for decomposing refractory minerals. 

These usually involve fusion with fluxes, such as sodium peroxide, 

sodium fluoride, mixtures of sodium fluoride and potassium pyrosulfate, 

and mixtures of sodium carbonate and sodium borate. One fusion 

gives nearly complete decomposition of minerals such as zircon, 

monazite, cassiterite, ilmenite, and betafite. Platinum crucibles are 

used for all these fusions except for sodium peroxide. Here either 

porcelain or iron crucibles may be used. Because these are specialized 

procedures, they are discussed in detail under the individual methods 

in other parts of this report.

GENERAL PROCEDURE

1. Weigh into a platinum dish 5 g of sample (ground to pass 60-80 

mesh) for samples with total radioactivity equivalent to 0.015 percent 

uranium or less; for samples of higher radioactivity, take a proportionately smaller sample.

2. If the sample contains organic matter, heat the sample over a 

burner, gently at first, gradually increasing the heat until the organic 

matter is burned off. Caution: sulfide ores, which may contain 

arsenic, lead, or antimony, should be ignited in porcelain.

3. Add 45 ml of (1+2) HN03 , cover the dish, and digest the sample 

on the steam bath for 30 minutes.

If most of the sample goes into solution by this treatment, decant 

most of the liquid through a small filter paper and wash the paper 

with a little hot water. Reserve the filtrate. Burn the paper in a 

small platinum crucible and transfer the ash to the original dish 

containing the reserved insoluble portion. Proceed to step 4.

If relatively little of the sample was dissolved by the treatment 

with (1+2) HN03 , proceed to step 4 directly.

4. Add 10 to 15 ml of HF and 10 ml of HN03 to the dish and slowly 

evaporate the mixture to dryness on a steam bath. Repeat if there 

is much unattacked material. Combine with any filtrate reserved 

in step 3 and evaporate the solution to dryness twice with HN03 to 

remove fluoride. ,

5. Moisten the residue with a little hot dilute HN0 3 , transfer the 

contents of the dish to a beaker, and wash the dish with water. Add 

10 ml of hot (1 + 1) HC1 to the dish to dissolve any residual stains and 

then transfer this solution to the beaker containing the sample.

6. Evaporate the solution to dryness. Follow by two more evaporations to dryness with HC1.

7. Digest the residue with 20 to 40 ml of (1 + 1) HC1 and filter. 

Wash with hot (1 + 1) HC1, Reserve filtrate,
14 METHODS OF ANALYSIS, URANIUM AND THORIUM

8. Ignite the residue in platinum, add a little HF and a drop of 

H2SO4 . Evaporate the solution on the steam bath and then fume off 

the excess H2SO4 . Sinter the residue with a minimum of Na2CO3 

and dissolve the cooled melt in (1 + 1) HC1.

If much SiO2 separates when the fusion is treated with (1 + 1) HC1, 

evaporate the solution to dryness in platinum, treat with HF and a 

few drops of H2S04 , and fume off the sulfuric acid until dry. Dissolve 

the residue hi (1 + 1) HC1 and add the solution to the main sample. 

If little or no Si02 separates when the fusion is treated with (1 + 1) 

HC1, add the solution to the previous nitrates.

9. Any hydrolytic precipitate may be filtered off and rejected if 

only uranium is to be determined (table 1). It must, however, be 

reserved if thorium is to be determined, as such precipitates may 

carry down thorium, especially if phosphate is present.

NONOCCLUSION OF URANIUM BY HYDROLYTIC 

PRECIPITATES

In the preparation of the solution of the sample, an insoluble 

hydrolytic residue that may contain niobium, tantalum, titanium, 

thorium, zirconium, tin, antimony, tungsten, with or without phosphorus, may be obtained. The experiments in table 1 show that 

these residues occlude no uranium.

To a mixture of the elements under investigation, as soluble ions, 

were added 10 ml of HC1 and 5 ml of HNO3 . The solution was 

evaporated to dryness three times with intermediate addition of 

io-ml portions of HC1. The dry salts were then digested with 10 ml

of (1 + 1) hydrochloric acid, diluted to 35 ml with water, and again 

digested, The insoluble material was filtered, ignited, and weighed.

Uranium was then determined in the filtrate. No uranium was 

occluded in the precipitates, as shown in table 1.

At the time these data were obtained we were interested in amounts 

Of Uranium convenient for colorimetric determination. We have no 

formal data on occlusion for tne smaller amounts of uranium handled

in the fluorimetric methods. However, our experience with the

small samples used in the flUOlimetric determinations has been that

here alSO nO Uranium is occluded by hydrolytic precipitates.
METHODS FOR DECOMPOSITION OF ROCK AND ORE SAMPLES 15 

TABLE 1. Experiments showing nonocclusion of uranium by hydrolytic precipitates

Amounts (mg)

U

0.6 

.6 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 .-3 

.3 

.3 

.3 

2.5

NbjOs '

100 

100

100 

100 

100

TajOj i

100 

100

100 

100 

100

TiOj

300

300

300 

300 

300

Zr02

70

70

70 

70 

70

SnOj

100 

100

100 

100 

100

WOa

105

105

105 

105 

105

SbaOj

100 

100

Bi

60

60

Ce2 0>

100 

100

HtPOt 

(85 

percent) 

(drops)

2

2

2

2

2

2

2

2

2

4 

4

Insoluble 

residue 

(mg)

230 

315 

98 

112 

08 

103 

t\ 

144 

0 

2 

105 

0 

0 

0 

5 

0 

0 

0 

870 

670 

670

U found infiltrate 

(mg)

0.6 

.6 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

.3 

2.7

i Added after NajCOs fusion.

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 3. THE GEOLOGICAL SURVEY CUPFERRON PRECIPITATION-EXTRACTION METHOD FOR THE DETERMINATION OF VERY SMALL AMOUNTS OF URANIUM IN 

NATURALLY OCCURRING MATERIALS

By F. S. GRIMALDI

CONTENTS

Page 

Abstract______-____---_---____-___-__.-_---___-__--_-.__-__-_- 17

Introduction __-_-___-__-__----_---_--_--__-____-__-_-___--__-__.__ 18

General method_________-______._-__________-._-_____..-__-____--_-_ 18

Outline and discussion._________________________________________ 18

Procedure __-___-_______-__-.__..__-_____-__-__-_-_-_-__--___-_ 20

Special methods for monazite, concentrates rich in titanium or zirconium, 

and other materials._--_-__-__-_---__-_---______-_____---__-_-___ 22

Experiments.____._______-_-_______-__-________-_____-__--__-__.-_ 24

Verification of general method________-______--_-__-_____-____ 24

Comparison of analytical results with those obtained by other methods. 24 

Removal of chromium by double precipitation by cupferron from 

reduced solution____________________________________________ 24

Removal of chromium by volatilization as chromyl chloride.________ 25

Effectiveness of ether and ethyl acetate in extracting cupferron

precipitates. _ _____-______-____-_---__--_____-__--_---_---_-- 26

Removal of cerium by precipitation with sodium hydroxide-hydrogen

peroxide_ ___---_-_--______-__-____-____-__-__-_--_____-.-- 27

TABLES

TABLE 1. Recovery of uranium from samples and synthetic mixtures__ _ 24

2. Chromium occlusion with uranium in samples high in chromium

after one reduction and precipitation with cupferron_ _______ 25

3. Removal of chromium by two reductions and precipitations with

cupferron-----_----_---_----_-----_--_-__--___-__-_---_ 25

4. Removal of chromium by volatilization as chromyl chloride..__ 26

5. Effectiveness of ether and of ethyl acetate in extracting cupferron precipitates.-____-___--__-___-__--__--_.--_-._--_ 27

6. Separation of cerium from uranium by sodium hydroxide-hydrogen peroxide ____-____-__-___-__-___-_____----------__-_ 27

ABSTRACT

Detailed procedures are given for the determination of very small amounts of 

uranium (as little as 0.002 percent) in naturally occurring materials of widely

NOTE. This report was Issued as Trace Elements Inv. Eept. 31C and AEOD 2631,1946.

17
18 METHODS OF ANALYSIS, URANIUM AND THORIUM

varying compositions. Uranium is concentrated by cupferron precipitation from 

reduced solution, then purified by cupferron precipitation and extraction of 

impurities after oxidation of uranium to the sexivalent state. Final determination is made colorimetrically in alkaline peroxide solution. Detailed procedures 

are presented, together with experimental data in support of the principal steps 

of the procedure.

INTRODUCTION

The object of the investigation was to develop a general method 

for the determination of very small percentages of uranium (as little 

as 0.002 percent) in naturally occurring materials. The samples to 

be analyzed included igneous and sedimentary rocks of various types, 

as well as placers, sands, and ores. Because of the complexity and 

diversity of these samples, special attention was given to the preparation of the solution and to several separation procedures to make 

certain that no uranium was lost and that all interferences were 

eliminated.

The literature available when this work was done contained no 

thoroughly tested methods for the determination of traces of uranium. 

Certain principles and separations in the unclassified literature for the 

determination of large amounts of uranium were tested to determine 

their suitability, with or without modification, for the problem at 

hand. After considerable investigation of the different procedures, 

it was found that separations by means of cupferron and the estimation of uranium colorimetrically by means of alkaline peroxide were 

the most satisfactory.

GENERAL METHOD

OTJTXINE AND DISCUSSION

1. Complete decomposition of sample (part 2).

2. Removal of nearly all the iron by extraction with ethyl acetate from (1+1)

hydrochloric acid solution.

3. Reduction followed by precipitation of uranium with cupferron; titanium, 

vanadium, or zirconium already present in the solution act as carriers.

(Separation from aluminum, calcium, and phosphorus.)

4. Ignition, fusion with oxidizing flux, and solution of the melt.

5. SeT>n.T-«.+,ion of the vn-anyV ion by ex-traction, of the cupferrates of other elements

with ethyl acetate.

6. Colorimetric estimation of uranium by alkaline peroxide.

For materials high in niobium, tantalum, titanium, zirconium, tin, or

vanadium, a preliminary extraction with ethyl acetate of the CUpferrateS 

of these elements is made from a large volume or solution to remove most or

these constituents.

Ill tlie preparation Of the solution^ h.ydrol^tic precipitates containing niobium, tantalum, titanium, zirconium, tin, tungsten, thorium,

and pnospWus may be formed even though the sample is completely
CUPFERRON PRECIPITATION-EXTRACTION METHOD FOR URANIUM 19

decomposed. These hydrolytic precipitates are filtered and discarded 

because they do not occlude uranium, whether the elements mentioned 

are present individually or together (part 2). However, monazite and 

samples rich in titanium, zirconium, and other elements that give large 

hydrolytic precipitates are more conveniently handled by a special 

method given on page 22.

Iron is removed by extraction with ethyl acetate or ether from 

a (1 + 1) hydrochloric acid solution of the sample. The excess acid 

is evaporated and the solution is made to (1+9) hydrochloric acid, 

the volume is kept as small as is consistent with solution of the salts. 

It is then passed through a small Jones reductor directly into an iced 

cupferron solution.

For solutions containing nickel, which interferes in the reduction 

of uranium, zinc amalgam containing 10 percent mercury is substituted 

for the usual 2 to 3 percent amalgam (part 5).

With ores containing metals of the acid hydrogen sulfide group, 

it may be necessary to pretreat the solution with zinc or with hydrogen 

sulfide to avoid the precipitation of these elements in the reductor. 

Passage through the reductor reduces uranium to the trivalent and 

quadrivalent states, both of which are quantitatively precipitated by 

the cupferron in the receiving flask.

The cupferron precipitation is made at acidities of (4+96) to 

(8+92) hydrochloric acid. Perchlorate and sulfate ions do not interfere. The cupferron will precipitate uranium together with iron, 

titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tin, and part of the tungsten that escaped previous separation. The process separates these from other elements such as aluminum, phosphorus, manganese, cobalt, nickel, calcium, and chromium 

in the solution.

Experience with actual rock samples showed that with relatively 

high chromium content and with large cupferron precipitates a little 

chromium is occluded (p. 24). The chromium gives a color similar 

to, but more intense than that of uranium in the photometric determination, so its complete removal is imperative. When necessary, 

this is done by repeating the reduction and precipitation with cupferron. It is also feasible (p. 25) to remove chromium before the 

reduction and precipitation, by volatilization as chromyl chloride 

from a boiling perchloric acid solution. 1 If the samples contain 

much potassium, the perchloric acid must be removed to prevent 

formation of a precipitate of potassium perchlorate; this is done by

i Smith, F. W., 1938, Volatilizing chromium as chromyl chloride: Ind. and Eng. Chem., Anal. Ed. 10, 

p. 360.
20 METHODS OF ANALYSIS, URANIUM AND THORIUM

adding ammonium chloride and heating to decompose the unstable 

ammonium perchlorate. 2

The cupferron precipitate is carefully ignited, and dissolved by 

fusion with potassium bisulfate, with the addition of sodium nitrate to 

insure that uranium is in the sexivalent state. The melt-is taken up 

in hydrochloric acid to make a (1 + 9) hydrochloric acid solution.

In the next step the solution, chilled with ice, is treated with 

cupferron and extracted with ethyl acetate. This separates the 

uranium from iron, titanium, zirconium, vanadium, molybdenum, and . 

other elements that form insoluble precipitates with cupferron; 

sexivalent uranium is not precipitated. These cupferron precipitates 

are completely extracted by ether or ethyl acetate; and the uranium, 

is left in the aqueous layer (p. 26). The solution at the start of the 

extraction of the cupferrates is (8+92) hydrochloric acid. In the 

extraction, most of the excess cupferron dissolves in the ethyl acetate. 

The extraction method avoids the uncertainty inherent in separation 

of a trace element in the filtrate from a precipitate.

Organic matter hi the aqueous layer is decomposed with nitric and 

sulfuric acids, and the nitrates are then removed. The uranium is 

then determined photometrically by the intensity of the yellow 

formed by adding hydrogen peroxide and making the solution alkaline;. 

the solution must first be filtered to remove hydrated oxides of rare 

earths that may have escaped previous separation. The amount of 

cerium and other rare earths accompanying uranium should be small. 

For example with cerium solutions, about 0.6 mg of cerium is found

in the first cupferron precipitate if the original solution contained 

25 mg of cerium. If 2 mg of cerium were originally present, enough

escapes separation to give a very faint, but definite yellow in the final 

sodium hydroxide-peroxide test. It is likely, that even more cerium

is carried down in the cupferron precipitate when other elements are 

present that are also precipitated. The precipitate of cerium in

Sodium hydroxide-peroxide solution has a color intensity abOUt tWlCC

that produced by an equal weight of uranium. Filtration of the

final sodium hydroxide-peroxide solution separates uranium 

quantitatively from cerium (p. 27).

PROCEDURE

1. Prepare a 1OO 15O ml hydrochloric acid solution (1 + 1) of the

sample (part 2).

2. Remove iron by two extractions with 50-100 ml ethyl acetate. 

Reject the ethyl acetate layers.

3. Evaporate the solution to dryness to eliminate the excess acid.

3 Noyes, A. A., and Bray, W. 0., 1927, A system ol qualitative analysis for the rare elements, New 

York, p. 237, 463, The Macmillan Co.
CUPFERRON PRECIPITATION-EXTRACTION METHOD FOR URANIUM 21

4. Add 10 ml of hydrochloric acid (1 + 1) and digest on the steam 

bath. Add 20 ml of water and digest until soluble salts dissolve. 

Filter if necessary and wash with water. Reject the hydrolytic 

residue.

5. Pass the solution, 50 ml in volume, through a Jones reductor 

10 to 12 inches long and of about X-inch bore. Collect the solution 

directly into 15 ml of 6 percent cupferron solution contained hi a 

125-ml Erlenmeyer flask immersed in an ice bath, shaking the flask 

during the passage. Wash the reductor column with 10 ml of 5 

percent hydrochloric acid and then with enough water to make the 

contents of the flask 100 ml. If no precipitate forms add 10 ml of 

titanium sulfate solution (1 ml=l mg Ti02) to act as carrier. If a 

large precipitate forms add more cupferron to insure an excess of the 

reagent. Let stand in the ice bath for about 5 minutes, stirring 

occasionally. Mix in a little paper pulp and filter. Wash with 

cold 6 percent hydrochloric acid containing 1.5 g of cupferron per 

liter.

6. Burn the cupferron precipitate in porcelain; start the ignition 

at low heat until the paper carbonizes, and increase the heat until 

the carbon is burned off. The final temperature should be about 

750° C.

7. If the solution (step 4) before passage through the reductor 

showed no visible green chromium, omit steps 7 and 8 and proceed 

directly to step 9. See "Experiments."

Fuse with a little potassium pyrosulfate. Keep the melt in quiet 

fusion until the residue is dissolved and any carbon that might be 

present due to faulty ignition of the cupferron precipitate is also gone. 

Allow the melt to cool. Dissolve the melt in 50 ml of water containing 

4.5 ml of hydrochloric acid.

8. Pass the solution through the reductor as in step 5. This 

second reduction is not necessary if the color of the solution before 

the first passage through the reductor (step 4) showed no visible green 

chromium.

9. Fuse the second ignited cupferron precipitate with potassium 

pyrosulfate. Keep the melt in quiet fusion until the residue is dissolved and any carbon that might be present is also gone. Cool. 

Add a little sodium nitrate (about 10-25 mg) and fuse again until 

the nitrate is gone. Cool and dissolve the melt in 30 ml of water containing 3.5 ml of hydrochloric acid. The nitrate insures complete 

oxidation of the uranium to the sexivalent state. Cool the solution 

hi an ice bath.

10. Transfer the solution to a separatory funnel. Add 15 ml of 

cold 6 percent cupferron solution. Shake several times. Add 20 ml
22

of cold ethyl acetate, shake, allow to settle, and separate the layers. 

Make two more extractions of the water layer with ethyl acetate. 

Reject the ethyl acetate layers.

11. Evaporate the water layer to a small volume. Add 15 ml of 

nitric acid and evaporate to dryness. Add 1 ml of sulfuric acid, cover 

with watch glass, and fume gently on the hotplate. Destroy the 

last trace of organic matter by cautious dropwise addition of 1 ml of 

nitric or fuming nitric acid. Allow to fume for 5 minutes after the 

nitric acid is gone. Repeat with a 1-ml portion of fuming nitric acid. 

Allow to fume 5 minutes after the nitric acid is gone. While the solution is still fuming, add cautiously 2 ml of water dropwise from a, 

pipette to remove any traces of nitrogen compounds, and again bring 

to fumes of sulfuric acid. Cool.

12. Add 35 ml of water and boil gently until a solution is obtained. 

The double sulfates of rare earths and potassium may precipitate. 

These are not filtered. Cool to about 50 C. Add six drops of 30 

percent hydrogen peroxide, then 50 percent sodium hydroxide solution drop by drop until neutral, then 1 ml in excess. Cool. Transfer 

to a graduated cylinder and dilute to 50 ml. Filter through a 7-cm 

Whatman no. 40 paper, but do not wash.

13. Compare the solution visually with solutions containing known 

quantities of uranium made up to 50-ml volume and containing 1 ml 

of 50 percent sodium hydroxide solution and five drops of 30 percent 

hydrogen peroxide. Narrow-bore Nessler tubes may be used for the 

visual comparison. Density measurements may also be made spectrophotometrically at about 400 m/i (part 3).

SPECIAL. METHODS FOR MONAZITE, CONCENTRATES 

RICH IN TITANIUM OR ZIRCONIUM:, AND OTHER

MATERIALS

The general method is modified for certain refractory HMtoialS for 

two reasons; (1) the cupferron precipitates obtained in step 5 are 

extremely bulky and are not easily handled, and (2) very large hydlOlytic precipitates are obtained. Although experiments Show no 

occlusion Of liraniUm ty moderately large hydrolytic precipitates, it 

is preferable to avoid their formation bj eliminating the bulk of the 

constituents by a preliminary ethyl acetate extraction of tnG CUpferrates from large volumes Of solution. The procedure foUows:

1. Fuse 0.5 g Of finely grOUnd Sample in a porcela.^, crucible With

3 g of sodium peroxide.

2. Tra^fer tKe crucible containing the COOled melt to an 800-ml 

beaker and add 225 ml 01 Wator, ^ -g to a gentle boil and allow tO
CUPFERRON PRECIPITATION-EXTRACTION METHOD FOR URANIUM 23

simmer for a few minutes to destroy most of the peroxide. Cool. 

Add slowly 225 ml of cold (1+4) hydrochloric acid solution. The 

purpose is to prevent the precipitation of silica at this point. Warm 

the sample gently if complete solution is not obtained. Cool in an ice 

bath. Samples containing both phosphate and elements like titanium 

and zirconium will give phosphate precipitates that are filtered and 

rejected before proceeding to the next step.

3. Transfer the cold solution to a 2-liter separatory funnel and add 

enough cupferron (generally 100 ml of 6 percent cupferron solution 

is enough) to precipitate elements giving insoluble cupferrates. Add 

300 to 400 ml of cold ethyl acetate and extract. Extract again with 

300 to 400 ml of ethyl acetate. Reject the ethyl acetate layers.

4. Evaporate the water layer to about 50 ml and add 50 ml of 

nitric acid. Evaporate to dryness.

5. Digest residue with dilute nitric acid and filter off silica. Reserve 

the solution. Ignite the silica and treat with hydrofluoric acid and 

a few drops of sulfuric acid. Evaporate and bring to fumes of sulfuric 

acid, then evaporate to dryness on the hotplate. Fuse the residue 

with a minimum of sodium carbonate. Leach the cooled melt with 

dilute hydrochloric acid and combine with reserved solution.

6. Evaporate the solution to dryness. Add hydrochloric acid and 

evaporate the solution to dryness to eliminate nitrate. Repeat with 

another portion of hydrochloric acid.

7. Dissolve the residue with 10 ml of (1 + 1) hydrochloric acid. 

Follow the general procedure from steps 4 to 13.

Silica occasionally will precipitate in step 2 of the special procedure. 

When this happens, the solution is taken to dryness to dehydrate the 

silica, and the silica is then filtered off. The silica may be contaminated with large amounts of hydrolytic oxides such as those of titanium and zirconium. The silica is volatilized with hydrofluoric acid 

and sulfuric acid, and the sulfuric acid is removed as before. The 

residue is fused with potassium pyrosulfate and then leached with a 

large volume of (1+9) hydrochloric acid. This solution and the 

filtrate from the silica are carried separately through the cupferronethyl acetate extraction, and are afterward combined. The cupferron 

is destroyed with nitric acid which is removed by repeated evaporations with hydrochloric acid. The solution, 50 ml in volume and 

containing 10 ml of hydrochloric acid (1 + 1) and a few milligrams of 

titanium is then carried through steps 5 to 13 of "General method."
24 METHODS OF ANALYSIS, URANIUM AND THORIUM

EXPERIMENTS

VERIFICATION OP GENERAL METHOD

Table 1 shows data on procedure discussed under "General method." 

TABLE 1. Recovery of uranium from samples and synthetic mixtures

Sample

Synthetic mixture '..

Do.. .... -- .

Do.- 

Do . .

Uin

sample

(nig)

0

0

0

0

U added

(mg)

0.30

.60

1.30

2.50

Total U

found

i (mg)

0.3

.6

1.3

2.6

Sample

Sample 65-67. .......

Do.. ............

Do.... .

Uinl

sample

(mg)

0.15

. .15

.50

.50

U added

(mg)

0

fifi

0

.30

Total U

found

(mg)

0.15

.75

.6

.3

i Synthetic mixture: 50 g quartz, 50 g albite, 50 g NasPOi-^HjO, 50 g CaCOs, 50 g PeaOj, 10 g MgCOs, 

10 g MnOa, 1 g chrome alum, 1 g VaOj, 0.2 g TiOj. The analyses were made on 5-g portions of the synthetic 

mixture after known quantities of uranium had been added.

COMPARISON OF ANALYTICAL RESULTS WITH THOSE OBTAINED 

BY OTHER METHODS

Typical results obtained hi the laboratory of the Geological Survey 

by the cupferron method described in this paper and by the carbonate 

method are given in table 2 (part 4) describing the latter method. 

Table 3 (part 4) shows results of both methods compared with the 

results obtained in two other laboratories where different procedures 

were used.

Uranium was determined 3 on 21 samples containing from 8 to 40 

mg of chromic oxide by double precipitation with cupferron after 

reduction. After the uranium Was determined by sodium hydroxidehydrogen peroxide, the solutions were tested for chromium by ether 

extraction of the chromium compound with peroxide, from ice-cold, 

barely acid solutions in tfllS manner; The alkaline peroxide solutions

(50 ml in volume) were made just acid With hyOjOCUOriC &Cld ft^d 

then barely alkaline again with a few drops of sodhim hydroxide. 

The Solutions W6f6 GOOlcd in an ice bath and transferred to a separatory funnel. Twenty-five milliliters of icfi-COld ether were added and 

hydrochloric acid drop by drop until the solutions were slightly add. 

Tll6 mixtures were shaken immediately and tixen allowed to settle 

The water layers were draWTl Off End treated again with alkali ether,

a.xxa. a.0va ^ tKe same manner three more tunes. This mBlllOu 01 

removal Of Chromium waa eugs * *«, ~s w Margaret D Foster of

this laboratory, and additional tfiStS COunTmed that Biniiill u^ , «

chromium may be removed Completely without loss of 

»Experimental work by W. G. Scilecht and F. B.
CUPFERRON PRECIPITATION-EXTRACTION METHOD FOR URANIUM 25

After four extractions, the solutions were made alkaline, a few drops 

of 30 percent peroxide added, and the uranium determined again. 

Table 2 gives typical results obtained with only one reduction. Table 

3 gives typical results obtained after two reductions. The decreases 

in intensity after ether extraction (table 3) are too small to be considered significant as evidence for the presence of chromium; even 

the highest discrepancy, 0.004 percent, occurred in a solution found 

to be free from chromium. Such decreases may be due to other 

causes such as the presence of organic matter, or the presence of 

nitrogen compounds in the final sodium hydroxide-peroxide test.

TABLE 2. Chromium occlusion with uranium in samples high in chromium, after 

one reduction and precipitation with cupferron

[Original chromium content from 8-42 mg CnOa]

Sample 

no.

CCM...

CO-19. -

JJ-20 

JJ-24 

JJ-29 

278 .,.

Apparent 

percent 

IT before 

extraction 

of Or

0.008

.011

.007 

.011 

.009 

.019

Percent 

U after 

extraction 

of Or

0.008

.007

.004 

.004 

.006 

.008

Difference

0

.004

.003 

.007 

.003 

.011

CrsOs 

occluded 

(mg)

0

.10

.06 

.12 

.05 

.20

Sample 

no.

658 ..

659......

1537..... 

1540. 

1541 

1544.....

Apparent 

percent 

U before 

extraction 

of Or

0.026

.026

.008 

.010 

.014 

.023

Percent 

U after 

extraction 

of Or

0.014

.013

.006 

.008 

.005 

.007

Difference

0.012

.013

.002 

.002 

.009 

.016

CrnOa 

occluded 

(mg)

0.24

.25

.03 

.03 

.20 

.30

TABLE 3. Removal of chromium by two reductions and precipitations with cupferron 

[Original chromium content of samples 8-42 mg CraOj]

Sample no.

174. 

175.. 

186. 

234.. 

278 

651 

655 

656.. 

657 

658. 

659.. 

Apparent 

percent U 

before extraction 

of Or

0.006

.011

.015

.009

.008

.006

.004

.007

.007

.014

.013

Percent U 

after extraction 

of Or

0.007

.011

.011

.009

.008

.006

.004

.007

.007

.014

.013

Difference

0.001

- 0

.004

0

0

0

0

0

0

0

0

Sample no.

660... .

661.. 

662.. 

721.... ..

722.. 

724..... ......

743.. 

744.. 

1285. 

1544. 

Apparent 

percent U 

Ibefore extraction 

of Or

0.004

.007

.005

.010

.009

.008

.008

.009

.013

.007

Percent U 

after extraction 

of Or

0.004

.007

.005

.008

.008

.006

.008

.007

.012

.007

Difference

0

0

0

.002

.001

.002

0

.002

.001

0

REMOVAL OF CHROMIUM BY VOLATILIZATION AS CHROMYL

CHLORIDE

Chromium* is oxidized to the sexivalent state by fuming with perchloric acid and is then volatilized,as chromyl chloride with sodium 

chloride. This procedure has been described by Smith.6 The perchloric acid remaining in the solution causes, in the later stages of the

< Experimental work by W. Q. Schlecht and F. S. Qrimaldi. 

»Smith, F.W., op. cit.

268681 54 3
26 METHODS OF ANALYSIS, URANIUM AND THORIUM

analysis, the precipitation of potassium perchlorate in samples containing sufficient potassium. To avoid this, the perchlorate is removed following essentially the same method described by Noyes and 

Bray. 6

The complete procedure follows:

After the extraction of iron from (1 + 1) hydrochloric acid solution 

by ethyl acetate, evaporate the solution to near dryness in a casserole. 

Add 5 ml of nitric acid and 15 ml of perchloric acid and bring to fumes 

of perchloric acid. Cover the casserole with a watch glass and 

strongly fume for a few minutes until the chromium is oxidized to 

chromate. Add 1 g of sodium chloride with a spatula and fuse until 

the chloride is eliminated. Bring to fumes of perchloric acid again 

and repeat twice with 0.5-g portions of sodium chloride. If the perchloric acid is greatly depleted it should be replenished before each 

addition of sodium chloride. Cool. Add 5 g of solid ammonium 

chloride, cover, and digest on the steam bath for about 30 minutes. 

Remove the cover and heat 'on the hotplate until excess perchloric 

acid is driven off. Now cover and heat strongly on the hotplate until 

a gentle deflagration takes place. Cool. Add 10 ml of (1 + 1) 

hydrochloric acid and digest on the bath. Follow the general method 

from step 4.

Five samples were tested in the above manner and the final sodium 

hydroxide-hydrogen peroxide solutions were tested for chromium by 

ether extraction of the perchromic acid. Table 4 shows the results 

obtained.

TABLE 4. Removal of chromium by volatilization as chromyl chloride

Sample no.

278 __ . ......

658.-.--. .

1543-. -- 

Apparent 

percent U 

before extraction of Or

.015

.009

Percent XI 

after extraction

of Cr

.014

.008

Difference

.001

Sample no.

1544

Apparent 

percent U

before extraction

of Or

0.006

Percent U 

after extraction 

ofCr

0.006

003

Difference

0

001

EFFECTIVENESS OF ETHER AND ETHYL ACETATE IN EXTRACTING 

oTTi'E'EitH.ON PRECIPITATES

The following tests were made to determine the effectiveness of

ether and ethyl acetate in extracting the precipitate forined with, 

cupferron. The test solutions had a volume of 30 ml and contained 

4 fflJ 01 IryUlOClUoric »wd, EO.OK solution was cooled in an ice bath

and 10 mi of cool 6 percent cupferron solution were added, TUe

mixture was extracted three times with 15-ml portions of ether or 

ethyl acetate. Either the aqueous layer or organic solvent layer was

6 Noyes, A. A., op. cit.
CUPFERRON PRECIPITATION-EXTRACTION METHOD FOR URANIUM 27

then tested for the elements in question after destruction of the 

organic matter (table 5).

REMOVAL OF CERIUM BY PRECIPITATION WITH SODIUM 

HYDROXIDE-HYDROGEN PEROXIDE

The use of solutions of cerium and uranium indicate that removal of 

cerium by the sodium hydroxide-hydrogen peroxide precipitation is 

nearly complete, and uranium is not occluded by the precipitate as 

shown in the experiments in table 6.

TABLK 5. Effectiveness of ether and of ethyl acetate in extracting cupferron

precipitates

Elements taken (g)

.018 Fc+'--._. --..-.-.......-.-....-.-....

.015 Ti-n+0.004 Fe« ...................

.025 C6^... ..............................

.014 V«+0.004 Fe«. ...................

.017 Mo«+0.004 Fc-n... ..................

.024 W+« (+0.7 ml 85 percent HaPOO-----

.024 W+H-0.004 Fe« (+0.7 ml 85 percent 

HsPOO- 

.017 Cr«+o.004 Fe«. .....................

.018 Zr+<+0.004 Fe+3.. .......... ..........

.022 Th+<+0.004 Fe«........ .............

.020 Sn+^........... ......................

Amount, in grams, left in nqucous 

layer after extraction with 

Ethyl acetate

0.000005 Fe. -

(') 

.025 Ce.........

<.000005V.......

.000005 Mo.....

.020 W. ........

.020 W. ........

.017 Cr......... (3) 

.018 Th...._-..

(0

Ether

0.000003 Fc...... (')

<.0~0~0~0~0~5~V..__._.

Method of detection

KCNS-acid. 

IfrOj-acid. NaOH-HzOs.z 

Phosphotungstic acid. 

SnCh-KCNS. 

Evaporation of ethyl acetate and ignition to 

WOa. 

Acid cinchoninc. 2

NazOs fusion. 2 

NH<OH. 

NH<OH. 

Acid H2 S.

' No titanium.

2 Ethyl acetate layer tested.

s No zirconium.

< No tin.

TABLE 6. Separation (in mg) of cerium from uranium by sodium hydroxide- 

. . hydrogen peroxide

Ce in 

solution

5.0

5.0

5.0

2.0

2.0

1.0

1.0

U in solution

0

0

0.3

0

.3

0

.3

U found in 

filtrate

0

0

.3

0

.3

0

.3

Cc in solution

0.2

.2

.1

. 1

.03

.03

U in solution

0

.3

0

.3

0

.3

U found in 

filtrate

0

.3

0

.3

0

.3

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 4. THE GEOLOGICAL SURVEY CARBONATE-PHOSPHATE-PEROXIDE METHOD FOR THE DETERMINATION 

OF VERY SMALL AMOUNTS OF URANIUM IN NATURALLY OCCURRING MATERIALS

By M. D. FOSTER and R. E. STEVENS

CONTENTS

Introduction._ ____________________________________________________ 29

Outline and discussion of procedure.....______---______-___-_______.- 30

Experiments ______________________________________________________ 34

Occlusion of uranium by the carbonate precipitate using synthetic 

mixtures.._ _________________________________________________ 34

Comparison of results obtained by this and other methods..._______ 35

The removal of titanium and vanadium by one carbonate precipitation_-__-_--___________----______-_-___-________-_____-_ 36

Effectiveness of the phosphate precipitation for the separation of

vanadium and uranium_____________________________________ 36

TABLES

TABLE 1. Determination of uranium in synthetic mixtures of known

uranium content____.____________-_.___.___._-___-__-_ 34

2. Comparison of results of uranium analyses by the carbonatephosphate-peroxide and the cupferron methods.___________ 35

3. Comparison of results of uranium analyses by different methods

in several laboratories.__________________________________ 35

4. Amount of titanium and vanadium removed from solution by

one carbonate precipitation...-------.------------------- 36

INTRODUCTION

A procedure is described for the determination of very small 

amounts of uranium (as little as 0.10 mg) in a wide variety of naturally occurring materials. Most of the constituents are separated 

from uranium by hydrochloric acid extraction (of iron) and by repeated precipitation with sodium carbonate, and the uranium is then 

coprecipitated with aluminum as the phosphate in acetic acid solution. The phosphate precipitate is dissolved in sodium hydroxide

NOTE. This report was Issued as Trace Elements Inv. Kept. 31B, 1946.

29
30 METHODS OF ANALYSIS, URANIUM AND THORIUM

peroxide solution, and uranium is determined colorimetrically. A 

discussion of the important features of the method, experimental 

work done in connection with the development of the method, and 

comparative results by this and other methods are given.

The published methods for the determination of uranium were 

either inadequate for the determination of the small amounts of 

uranium (as little as 0.002 percent) sought in this study, or not applicable in the presence of phosphate, a major constituent of some of 

the samples to be analyzed. Methods developed at other laboratories 

were not available to us when this work was done. It was necessary, 

therefore, to develop methods especially designed for the determination of small amounts of uranium in the presence of large amounts of 

phosphate.

OUTLINE AND DISCUSSION OF PROCEDURE

The main features of the method are as follows:

1. Complete decomposition of the sample (part 2).

2. Removal of most of the iron (and molybdenum) by extraction with ethyl 

acetate from a (1 + 1) hydrochloric acid solution.

3. Removal of calcium, magnesium, titanium, zirconium, chromium, manganese, most of the rare earths, and some of the aluminum and phosphate 

by precipitation with sodium carbonate.

4. Coprecipitation from acetic acid solution of uranium and aluminum as 

phosphates. This step also separates vanadium from uranium.

5. Colorimetric determination of uranium in sodium hydroxide solution containing hydrogen peroxide.

The sample is decomposed and a solution in (1 + 1) hydrochloric 

acid is obtained by methods given in part 2. Complete decomposition 

is essential as it is not safe to assume that no uranium is present in

undecomposed material. Any hydrolytic precipitates of tantalum, 

niobium, tin, titanium, zirconium, or tungsten may be ignored, howererj as they do not occlude uranium. If; however, the sample is

used also for the determination of thorium, the hydrolytic precipitates should be reserved, as they may occlude thorium.

Although iron is removed from the solution by precipitation with

sodium carbonate, the amount in a 5-g sample forms such a bulky

precipitate that it is desirable to remove iron before the carbonate 

precipitation. Removal of iron is also desirable if the sample is used

for the determination of thorium as well as of uranium. Extraction

with ethyl acetate from hydro chloric acid solution affords a quick and

m.on/t-ly cco-Kxvxklofce Tiro-eno-v-cil of i:ro:rx £n,:rvd Trr-iol yt>d <2T->n:r»-> ^ from tin o solution

The carbonate precipitation, with cooling before filtration, removes

calcium, magnesium, titanium, zirconium, chromium, manganese, 

thorium, most of the rare earths, and part of the aluminum and 

phosphate from uranium that is left in solution. However, the 

precipitate may occlude some uranium, and it is,therefore advisable
CARBONATE-PHOSPHATE-PEROXIDE METHOD FOR URANIUM 31

to make a second or even third precipitation. The amount of uranium 

retained in the first carbonate precipitation depends on the amount 

of uranium present and on the bulk of the carbonate precipitate. 

With the amount of precipitate expected from a 5-g sample of most 

rocks, less than 4 percent of the uranium is retained after two precipitations if the uranium content is less than 2 mg (p. 34). With the 

amount of precipitate expected from a 2-g sample, less than 2 percent 

of the uranium is retained after two precipitations if the uranium 

content is less than 20 mg.

Thorium is precipitated quantitatively by sodium carbonate under 

the conditions used, and may therefore be determined in the same 

sample. The method is given in part 19.

Precipitation of uranium as the phosphate in acetic acid solution, 

with ultimate solution in sodium hydroxide, makes it possible to 

obtain the uranium in a smaller volume for colorimetric comparison. 

It is necessary, however, to use some other element as a collector for 

the very small amounts of uranium for which this method was designed. 

Aluminum was chosen because (1) it forms a phosphate insoluble in 

acetic acid, (2) its phosphate and hydroxide are soluble in excess 

sodium hydroxide, and (3) it gives no colored compounds to interfere 

in the colorimetric determination of the uranium.

The phosphate precipitation also separates most of the vanadium 

from the uranium (p. 36). Double precipitation as phosphate may 

be necessary if the vanadium content is relatively high. The complete 

removal of vanadium is unnecessary, as it produces a color in the 

sodium hydroxide-peroxide solution that is much lower in intensity 

than that of uranium (p. 36) and this slight interference may'be 

overcome by boiling the solution before making the color comparison 1 

(p. 33, step 9).

Small amounts of rare earths may be carried through the phosphate 

precipitation. These are precipitated by the sodium hydroxideperoxide treatment. Filtration of the sodium hydroxide-peroxide 

precipitate separates uranium quantitatively from cerium (part 3). 

If the sodium peroxide precipitate is large, it should be dissolved in 

acid and reprecipitated to recover any uranium that might be occluded.

The final sodium hydroxide-peroxide solution used for the colorimetric comparison may occasionally have a brownish hue due to 

colloidal hydrated iron oxide. This may be removed by filtering after 

warming the solution on the steam bath to precipitate the iron.

The use of 30 percent hydrogen peroxide is specified because 3 

percent hydrogen peroxide contains organic preservatives, such as 

acetanilide, which give in alkaline solution a yellow color similar to

1 Qoldbeck, C. Q., Petretic, O. J., Minthorn, M. L., and Rodden, C. J., 1945, Colorimetric determination of uranium by means of peroxide: Nat. Bur. Standards Report A-1074.
32 METHODS OF ANALYSIS, URANIUM AND THORIUM

that of uranium. This interference may be serious for very small 

amounts of uranium.

1. Decomposition of sample: Weigh out 5-g of the sample if it has 

a total radioactivity, by counting, equivalent to 0.015 percent uranium 

or less. Use proportionately smaller weights of samples having higher 

radioactivity. Prepare a hydrochloric acid solution of the sample 

(part 2). If thorium is to be determined on the same sample, do not 

filter any hydrolytic precipitate that may have formed during the 

decomposition of the sample. If thorium is not to be determined on 

the same sample, the hydrolytic precipitate may be filtered off.

2. Extraction of iron: After obtaining a (1 + 1) HC1 solution of the 

sample, evaporate down to a volume about 25 ml. Transfer the solution to a 250-ml separatory funnel and shake with 40 ml of ethyl 

acetate. After the two layers have separated, draw off the acid layer 

into another separatory funnel of the same size. Add 20 ml of ethyl 

acetate, shake well, and, after the layers have separated, draw off the 

acid layer into a 400-ml beaker. Combine the ethyl acetate layers 

and wash once by shaking with 5 ml of (1 + 1) HC1. Add the washings to the acid layer in the 400-ml beaker.

3. Dilute the acid solution from the extraction of iron to a volume 

of about 250 or 300 ml and heat to boiling. Remove the beaker 

from the heat and slowly add 50 percent NaOH solution until a 

slight permanent precipitate forms, then add solid Na2C03 very 

carefully until effervescence ceases. Add 2 or 3 g of Na2C03 in excess 

and stir until all the Na2C03 is dissolved. Place the beaker in a 

cold water bath for about 45 minutes and filter on a Whatman no. 

40 12.5-cm paper. Wash once with a 1 percent Na2CO3 solution.

4. Allow the precipitate to drain well, transfer to the precipitation beaker with a fine stream of distilled water, and add 7 ml of 

HC1. Dilute the solution to 250 or 300 ml, heat to boiling, and 

reprecipitate as before with 50 percent NaOH and solid Na2C03 .

Cool and filter on a Whatman no. 40 12.5-cm paper. Scrub out the 

beaker and wash the precipitate on the paper five times with a

i percent solution of Na2 co3 . Add the filtrate and washings to the 

filtrate from the first precipitation. Make the combined filtrates 

acid with concentrated HC1, then add 2 ml in excess, and note the 

approximate amount of aluminum precipitated as the neutral point 

is passed.

5. Reduce the volume of the combined filtrates to about 150 ml

(time can be saved if the filtrate from the first carbonate precipitation 

is made acid and evaporated during the second precipitation and 

filtration). If, in the process of neutralizing and acidifying the fil-
- CARBONATE-PHOSPHATE-PEROXIDE METHOD FOR URANIUM 33

trates, they were found to contain little or no aluminum, add 7 to 10 

ml of an A1C1 3 solution containing 6.7 mg of A1C13 in 1 ml. If the 

filtrates contain some aluminum, add 4 ml or less of the A1C13 solution, 

depending on the amount of aluminum present. If on addition of 

the aluminum a precipitate forms, add sufficient HC1 to dissolve it. 

Then add 1 g of solid (NH4) 2HP04 and heat to boiling. Remove the 

beaker from the heat and add NH4OH until the solution is just alkaline to methyl red; then add, dropwise, sufficient ammonium acetateacetic acid solution (containing 308 g of ammonium acetate and 460 

ml of acetic acid per liter) to make the solution distinctly acid to 

methyl red. Boil the solution (with precipitate) for about 1 minute 

and digest it on the steam bath for 30 minutes.

ft. Filter on a Whatman no. 42 9-cm paper and wash the precipitate 

five tunes with a solution containing 20 ml of the ammonium acetateacetic acid solution in 100 ml of water.

7. After the precipitate has drained, transfer it from the paper to 

a 100-ml beaker with a fine stream of distilled water, keeping the 

volume below 50 ml. Add HC1 dropwise until the precipitate just 

dissolves, then 2 ml of HC1 in excess. Add three drops of 30 percent 

H202. Estimate the vanadium content from the color developed. 

If the solution contains (a) more than 3 mg of vanadium, proceed 

with step 8; (b) if 1 to 3 mg of vanadium, proceed with step 9; (c) 

less than 1 mg of vanadium, proceed with step 10 of the procedure.

8. If more than 3 mg of vanadium are present, transfer the solution 

to a 250-ml beaker, dilute to about 150 ml, add 2 g of NaCl, and proceed with the precipitation, digestion, filtration, washing, and solution 

of the phosphate as in steps 5, 6, and 7 above. Uranium is then 

determined by the procedure in step 10 below.

9. If 1 to 3 mg of vanadium is present, add 6 drops of 30 percent 

HzOz, make the solution just alkaline with 50 percent NaOH solution, 

then add 5 ml in excess. Heat the solution to boiling; boil 1 or 2 

minutes. Cool, adjust the volume to 50 ml, and proceed with the 

filtration and comparison as in step 10 below.

10. If less than 1 mg of vanadium is present, add 6 drops of 30 

percent EUOz, make, the solution just alkaline with 50 percent NaOH 

solution and then add 5 ml in excess. Adjust the volume to 50 ml 

and filter through a paper previously treated with a sodium hydroxideperoxide solution of the same concentration as the sample solution. 

Compare the filtered solution visually in Nessler tubes with uranium 

standards containing the same amounts of NaOH and H202 in the 

same volume. The optical density of the solution may be measured 

with a spectrophotometer at 400 m/u wavelength, and the amount 

of uranium determined by reference to a standard curve.
34 METHODS OF ANALYSIS, URANIUM AND THORIUM

EXPERIMENTS

OCCLUSION OF URANIUM BY THE CARBONATE PRECIPITATE 

USING SYNTHETIC MIXTURES

The procedure described above was tested by determining uranium 

in solutions of known uranium content. These solutions were prepared by adding different amounts of a standard uranium nitrate 

solution (1 ml=0.5 mg U) to 15 ml or 35 ml of a synthetic mixture. 

This was a solution containing 10 percent HC1 and, per liter, 10 g 

CaCl2 , 20 g Na3PO4 -12H2O, 30 g A1C13 -6H20, 5 g MgCl2 -6H2 0, 1 g 

MnCl2 '4H2O. The results obtained are given in table 1.

TABLE 1. Determination of uranium in synthetic mixtures of known uranium

content

Sample no.

1_ . - . .

2_. .

3...........................

4 ___________

5.----....-.-........

7 - . 

8. .. .....................

9... ....... - .._--.... .

Amount 

of 

sample 

(ml)

35 

35 

35 

35

35 

15 

15 

15 

15

Uranium 

added 

(mg)

0.25 

.50 

1.00 

 1.50 

2.00 

2.00 

5.00 

10.00 

20.00

Uranium recovery

From 1st 

carbonate 

precipitation (mg)

0.23 

.45 

.80 

1.15

1.42 

2.01 

4.65 

8.30 

18.00

Percent

92 

90 

80 

76.7

71 

100.5 

93 

83 

90

From 2d 

carbonate 

precipitation (mg)

(') 

(0 

0.20 

.32 

.50 (') 

.34 

1.62 

1.76

Total 

mg

0.23 

.45 

1.00 

1.47 

1.92 

2.01 

4.99 

9.92 

19.76

Total 

percent

92 

90 

100 

98 

90 

100 

100

99

99

1 Uranium not determined.

In these tests, the filtrates from the first and second carbonate 

precipitations were not combined as directed in the procedure, but 

were carried through independently to determine the degree of 

recovery of uranium after one and after two carbonate precipitations.

To simulate the amounts of accompanying constituents when

5 g of sample are taken for analysis, 35 ml of the synthetic mixture

Were USed for the tests With the smaller amounts of uranium (tests

nos. 1-5). For those tests to which 2 mg or more of uranium were 

added, 15 ml of the synthetic mixture, representing the amount of 

accompanying constituents to be found in 2 to 2.5 g of sample, were

used.

The results on the tests indicate that (1) as the amount of uranium 

present was increased, the percentage recovery after one carbonate 

precipitation decreased but that (2) after two carbonate precipitations, 

the recovery of uranium (on the amounts used in the tests) amounted 

to at least 96 percent. If the amount of uranium present is greater

than 20 mg, the percentage of recovery may decrease, ai^o^gh tllis

may be offset to some extent by the smaller sample taken for analysis 

and the consequent smaller bulk of carbonate precipitate obtained 

that results in less occlusion of uranium. If it is suspected, however,
CARBONATE-PHOSPHATE-PEROXIDE METHOD FOR URANIUM 35

that a sample has a high uranium content, three or even four carbonate precipitations should be made, unless analysis of the filtrate 

from the second carbonate precipitation alone indicates that the 

separation of the uranium is nearly complete.

COMPARISON OF RESULTS OBTAINED BY THIS 

AND OTHER METHODS

Results for uranium obtained by the carbonate-phosphate-peroxide 

method are compared in table 2 with results obtained by the cupferron 

method (part 3) developed in the laboratory of the Geological Survey. 

The samples include a wide variety of rock types.

TABLE 2. Comparison of results of uranium analyses by the carbonate-phosphateperoxide and the cupferron methods

Sample no.

MB 6-79.. ...............

65-7......................

MB 6-86... 

BC 59-480. ...............

BC 100-815...............

BC 101-825...............

BC 90-738.. ..............

Percent uranium

Carbonate 

method

0.002 

.003 

.003 

.005 

.006 

.006 

.006

Cupferron 

method

0.004 

.003 

.005 

.006 

.005 

.006 

.007

Sample no.

BC 67-542................

MOR 5-295.. ............

21-3. .....................

150-9-04..................

21-2......................

BCX-22... ...............

Percent uranium

Carbonate 

method

0.007 

.007 

.013 

.016 

.026 

.036

Cupferron 

method

0.007 

.009 

.012 

.014 

.028 

.038

Table 3 shows the results of analysis for uranium obtained by the 

carbonate-phosphate-peroxide and cupferron methods in the Geological Survey laboratory as compared with results obtained on the 

same samples by other laboratories using different procedures. 

Although the carbonate-phosphate-peroxide procedure is designed 

particularly for the determination of very small amounts of uranium, 

the results obtained on samples 12 and 13 indicate that the method 

can also be used for the determination of larger amounts. Larger 

amounts are not determined colorimetrically, but volumetrically 

(on the filtrate from the phosphate precipitation) after reduction.

TABLE 3. Comparison of results of uranium analyses by different methods in

several laboratories

Sample no.

1.... .... ........

2.. ... .. ......

3...... ..........

4....... .. .......

5 

6.. .... .

7 .............

Percent Us Os

A

0.035 

.07

.09 

.15 

.19 

.19 

.20

B

0.038

.11 

.14 

.15 

.19 

.18

C

0. 034 

.07

.11 

.10 

.16 

.23 

.17

D

0.029

.15

.18

Sample no.

8..... ...........

9. ............ ...

10 

11.............

12...... ...

13-----.....

Percent UsOs

A

0.26 

.35 

.38 

.56 

1.98 

23.62

B

0.28 

.32 

.35 

.57 

2.15 

23.41

C

0.33 

.36 

.41 

.57 

2.28 

23.35

D

0.38 

.40 

.55 

2.07 

23.30

A. Geological Survey, carbonate-phosphate-peroxide method. M. D. Foster, analyst. 

B. Geological Survey, cupferron method, F. S. Grimaldi and W. Q, SclUegljt. analysts. 

C. National Bureau of Standards. 

P. Princeton University.
36 METHODS OF ANALYSIS, URANIUM AND THORIUM

THE REMOVAL OF TITANIUM AND VANADIUM BY ONE CARBONATE

PRECIPITATION

To determine the effectiveness of the carbonate precipitation for 

the separation of titanium and vanadium from uranium, known 

amounts of these elements were added to 35 ml of a synthetic mixture 

(p. 34), a carbonate precipitation was made as directed in the procedure, and the filtrate was tested for titanium and vanadium.

The results obtained, which are given in table 4, indicate that the 

removal of titanium by one carbonate precipitation is nearly complete. 

The amount retained in the filtrate is so small that it would cause no 

interference in the colorimetric determination of uranium with hydrogen peroxide in alkaline solution. As expected, little vanadium is 

removed from solution by the carbonate precipitation. Presumably 

the amount that was removed in this test was occluded by the carbonate precipitate and would be recovered on a second precipitation.

TABLE 4. Amount of titanium and vanadium removed from solution by one carbonate

precipitation

Sample no.

!__.._ ___ .............. .... .... ....

o

Ti added 

(mg)

10

Ti in filtrate 

(mg)

0.2

V added 

(mg)

10

V in filtrate 

(mg)

7.1

EFFECTIVENESS OF THE PHOSPHATE PRECIPITATION FOR THE 

SEPARATION OF VANADIUM AND URANIUM

The principal purpose of the phosphate precipitation in this procedure is to separate vanadium from uranium. Tests indicate that

the filtrate, from a phosphate precipitation on a sample containing 

10 mg of vanadium, contained 8.6 mg of vanadium, but 1.4 mg 

remained in the precipitate. However, this amount of vanadium,

carried in the phosphate precipitate with uranium and subsequently

into the sodium hydroxide-peroxide solution on which the colorimetric 

comparison is made, does not interfere seriously in the determination 

of uranium, as it causes a color equivalent to only about 0.1 mg of

uranium.
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 5. ELIMINATION OF INTERFERENCE BY NICKEL IN 

THE DETERMINATION OF URANIUM BY MEANS OF 

ZINC AMALGAM REDUCTORS

By F. S. GRIMALDI

CONTENTS

Page 

Abstract ..--_-_-_._.________________________________...._ 37

Introduction. _____________________________________________________ 37

Poisoning by nickel in hydrochloric acid solutions____.--_--__--______ 38

Nonpoisoning of the "10 percent" Jones reductor in sulfuric acid solutions. 39 

Nonpoisoning of the "10 percent" Jones reductor in hydrochloric acid

solutions. _______________________________________________________ 40

Behavior of vanadium, titanium, and molybdenum on reduction in the

"10 percent" Jones reductor______________________________________ 40

Preparation of the "10 percent" Jones reductor______---__-____.____ 40

TABLES

TABLE 1. Poisoning of reductor by nickel in hydrochloric acid solutions. . 38

2. Elimination of nickel interference with the "10 percent" reductor. _______________________________________________ 39

3. Test of the "10 percent" reductor with hydrochloric acid solu-

--_..--___-_--.__--_-_--__-_-_-__-_-_.______ 40

ABSTRACT

Previously reported observations that zinc amalgam reductors are poisoned by 

sulfuric acid solutions containing nickel are confirmed; experiments show that 

poisoning also occurs with nickel in hydrochloric acid solutions. The effect is 

caused by deposition of nickel on the amalgam surface that promotes the vigorous 

evolution of hydrogen. This interference is easily overcome by using a solid 

amalgam richer in mercury than usual; this lowers the activity of the zinc enough 

to prevent deposition of nickel.

A Jones reductor containing a zinc amalgam consisting of 10 percent mercury 

by weight does not become poisoned by passage of nickel-bearing solutions through 

the reductor. Either hydrochloric acid or sulfuric acid solutions may be used. 

The valence changes during reduction of the elements commonly determined by 

means of the Jones reductor are the same for the "10 percent" reductor as with 

the standard reductor.

INTRODUCTION

One of the most useful tools for the chemical determination of 

uranium has been the Jones reductor. Its performance has been the

NOTE. This report was issued as Trace Elements Inv. Eept. 23 and AECD 1815,1946.

37
38 METHODS OF ANALYSIS, URANIUM AND THORIUM

subject of many studies. Recent work by J. B. Heberling* has shown 

that the Jones reductor quickly becomes poisoned by passage of 

solutions containing nickel through the reductor. He used a zinc 

reductor amalgamated with about 2 percent by weight of mercury. 

Working with sulfuric acid solutions containing about 0.2 g of uranium 

and 0.04 g of nickel, Heberling concluded that only 6 to 10 samples of 

comparable nickel content could undergo 100 percent reduction in a 

standard reductor. Because of this interference, it has been necessary 

to remove nickel by electrolysis with a mercury cathode or to reduce 

the uranium by shaking with a liquid zinc amalgam.

This work was undertaken to overcome the poisoning difficulties, 

so that the convenient standard procedure using the Jones Reductor 

could be retained.

POISONING BY NICKEL IN HYDROCHLORIC ACID

SOLUTIONS

The first experiments show that poisoning by nickel also occurs 

from hydrochloric acid solutions. Seven solutions were made, each 

solution had a volume of 45 ml. Six solutions contained 0.15 g of 

nickel, 0.1117 g of iron, and 4.5 ml of hydrochloric acid as the only 

acid. One solution contained 0.0279 g of iron. These were passed 

consecutively through the Jones reductor filled with a zinc amalgam 

containing 3 percent by weight of mercury. The solutions were 

titrated with O.lN potassium dichromate using diphenylamine as 

internal indicator after the addition of phosphoric acid. Iron instead 

Of uranium was chosen as the element to be reduced because of the 

certainty of valence change after reduction. Table 1 shows the results

obtained.

TABLE 1. Poisoning of reductor by nickel in hydrochloric acid solutions

Solution no.

I...... ...

2....... ... 

'L..... .......

4... -..-.

Amounts taken (g)

Fe

0.1H7 

. 1117 

.1117 

.1117

Ni

0.15 

.15

.15

.15

Fe found 

after reduc- tion (g)

0. 1115 

.1112 

.1079 

.1072

Solution no.

5.............

6 . 

7... - 

Amounts taken (g)

Fe

0.1117 

.1117 

.0279

Ni

0. 15 

.15 

.15

Fe found 

after reduction (g)

0. 1055 

.1047 

.0275

The results show that the reductor became poisoned after about 0.3 g

Of nickel passed through, and that this poisoning Occurred in. kydrochloric acid solutions, as well as in. the s^ifuric acid solutions studied

by Hebeiiing. Solution 7 indicated that more nearly 100^ percent 

reduction is obtained for smaller quantities of iron. This is to D6 

expected because there is a larger area of zinc per weight of iron. As

' Heberling, J. B., 1944, Kept. 1040, Sec. 2F.
ELIMINATION NICKEL INTERFERENCE IN URANIUM REDUCTION 39

observed by Heberling in using sulfuric acid solutions, metallic nickel 

was deposited, darkened the reductor, and promoted the evolution 

of hydrogen. The evolution of hydrogen was so vigorous that after 

solution 7 had been passed through the reductor, it was almost impossible to get another sample through the reductor. This vigorous 

evolution of hydrogen probably interferes with the proper contact of 

the solution with the zinc amalgam.

NONPOISONING OF THE "10 PERCENT" JONES REDUCTOR 

IN SULFURIC ACID SOLUTIONS

Amalgamating the zinc so that the mercury content was 10 percent 

by weight reduced its activity sufficiently so that no nickel plated out 

in the reductor and the poisoning difficulties were eliminated.

Solutions were prepared to have a total volume of 45 ml; they 

contained 0.15 g nickel and 0.1561 g uranium (average of three 

standardizations) and 10 percent by volume of sulfuric acid. The 

solutions were passed through the "10 percent" reductor, the preparation of which is described in a later section, at the rate of about 40 

ml per minute and were washed with 3 percent sulfuric acid and 

enough water so that the final sulfuric acid concentration after 

reduction was about 4 percent by volume. The solutions were 

aerated for 5 minutes, because the color of the solution indicated the 

presence of trivalent uranium. They were then titrated with standard 

potassium permanganate solution (0.02980N). The results are 

given in table 2.

TABLE 2. Elimination of nickel interference with the "10 percent" reductor

Solution no.

1.... ......

2.............

3.. 

4.... _ ......

5..... ........

6. .... .....

7. 

8.. ... .... .

9.............

10. 

11 

12..... .......

13............

14..... .......

15... 

16 ......

17..... .......

Amount taken (g)

U

0. 1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

. .1561 

.1561

Ni

0 15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15 

15

U found (g)

0. 1561 (') 

.1561 (>) 

.1561 (') 

.1562 (') 

.1560 (') 

.1560 (') 

.1561 (') 

.1561 (') 

0)

Solution no.

18.. ..........

19. 

20 

21 

22. 

23 

24. ........

25 

26.. 

27 . 

28 

29. 

30.. ...-.

31 

32.. ...

33.... .. ......

34 

Amount taken (g)

U

0. 1561 

.1561 

.1561 

.1561 

. 1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561 

.1561

Ni

0.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15 

.15

U found (g)

0. 1562 (') 

(') 

.1561

8

.1560 (') 

(') 

.1562 (') 

0) 

.1562 ('} 

0) 

.1561 

.1561

i Not titrated.

The results show that the reductor was not poisoned even after 

more than 5 g of nickel had passed through x it. This corresponds to 

the reduction of more than 100 samples of the kind of uranium ore
40 METHODS OF ANALYSIS, URANIUM AND THORIUM

normally analyzed. It must be noted also that the amount of nickel 

used in each experiment was at least three times the amount usually 

found and that with these amounts no poisoning of the reductor 

ensued. No gas evolved even with sample 34. After the experiments the reductor looked like new.

To determine if any nickel had actually plated out on the reductor, 

the top inch of amalgam was removed and dissolved in aqua regia, 

A qualitative test with dimethylglyoxime showed no nickel.

NONPOISONING OF THE "10 PERCENT" JONES REDUCTOR 

IN HYDROCHLORIC ACID SOLUTIONS

The 10 percent Jones reductor was further tested on solutions 

containing hydrochloric acid as the only acid. Eleven test samples 

were made up; each contained exactly 0.1117 .g iron, 0.15 g nickel, 

and 4.5 ml hydrochloric acid in a total volume of 45 ml. These 

solutions were reduced with the "10 percent" reductor and titrated 

as before. Again no poisoning resulted as shown in table 3.

TABLE 3. Test of the "10 percent" reductor with hydrochloric acid solutions

Solution no.

1.......... 

4... -

5..... ........

Amounts taken (g)

U

0. 1117 

.1117 

.1117 

.1117 

.1117 

.1117

Ni

0.15 

.15 

.15 

.15 

.15 

.15

U found (g)

(0 (') 

(') 

(') 

(') 

(')

Solution no.

7 ~~

8 - 

9............

10..... ....

11..-....- 

Amounts taken (g)

U

0. 1117 

.1117 

.1117 

.1117 

.1117

Ni

0.15 

.15 

.15 

.15 

.15

U found (g)

(0 

0. 1117 

.1118 

.1117 

.1117

i Not titrated.

BEHAVIOR OF VANADIUM, TITANIUM, AND MOLYBDENUM ON KEDTJCTION IN THE «io PERCENT" JONES

REDUCTOR

Tests made on sulfuric acid solutions showed that the 10 percent 

j<>xxos ^odxrctor reduces vanadium to the bivalent State, titanium 

and molybdenum to the trivalent state, These vaien^ cKo,nsos ^& 

identical with those obtained by use of a standard Jones reductor;

thus elements may be determined by the usual procedures after 

redaction, wltk a 10 percent Jones reductor.

PREPARATION OF THE "10 FERCENT" JONES REDUCXOR

Preparation oftiw "10percent" amalgam Dissolve 23.6 g mercuric

chloride in 400 fill Of Water contaiai^g about 10 ml of nitric acid. 

Transfer the solution to a 500-ml separatory funnel. Ada ISO g Oi 

20-mesh zinc and immediately shake. Shake for about 2 minutes;
ELIMINATION NICKEL INTERFERENCE IN URANIUM REDUCTION 41

release any gas pressure from time to time. Wash the amalgam with 

dilute sulfuric acid, and then wash thoroughly with water.

Preparation of the reductor column. The reductor used for all tests 

described had an inside diameter of 11 mm and was filled with 12# 

inches of zinc amalgam. To prepare, first add a little water to the 

tube and introduce about an inch of the amalgam at a time, gently 

tamping it in place with a glass rod.

268681 54 4

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 6. THE VISUAL FLUORIMETRIC DETERMINATION OF 

URANIUM IN LOW-GRADE ORES

By F. S. GRIMALDI and HARRY LEVINE

CONTENTS

Abstract_ ________________________________________________________ 43

Introduction. _____________________________________________________ 43

Discussion and procedure.._________________________________________ 44

Procedure ________________________________________________________ 46

Analytical results and extraction behavior of other elements._-___-.____ 47

TABLES

TABLE 1. Comparison of results of uranium determinations by three

methods of analysis_-___-------------_-------_---------- 48

2. Comparison of results of uranium determinations obtained by

fluorimetric and colorimetric procedures ___________________ 48

3. Extraction of some other elements with ethyl acetate.__-___-- 48

ABSTRACT

A simple visual fluorimetric procedure is described for the determination of 

0.001 to about 0.04 percent uranium in low-grade shale and phosphate ores. 

Using aluminum nitrate as the salting agent, the procedure employs batch extraction of uranyl nitrate by ethyl acetate. The uranium is fused with a fluoridecarbonate flux and the fluorescence intensity of the cooled melt is compared 

visually with standards. The initial decomposition of the sample by fusion with 

a sodium hydroxide-sodium nitrate flux is rapid, and the extraction is made from 

acid solution without removing silica and other hydrolytic precipitates. Aluminum nitrate effectively complexes fluoride, sulfate, and phosphate ions and thus 

eliminates the need for their removal.

INTRODUCTION

The exceedingly sensitive fluorescence of uranium fluoride phosphors under ultraviolet light has been used extensively for the quantitative estimation of uranium in a variety of materials. It is desirable 

to isolate the uranium first because many elements interfere seriously 

by quenching the fluorescence. For example, less than 10 microNOTE. This report was issued as Trace Elements Inv. Kept. 47 and AECD 2824, 1948.

43
44

grams of chromium reduces the fluorescence of uranium. The critical 

factor in the quenching phenomenon was found by Price * to be the 

concentration of the quenching element in the flux, not the ratio of 

the concentrations of quencher to uranium in the sample.

Two types of procedures have appeared in the project literature to 

circumvent quenching interferences. One developed by Price and 

coworkers employs a dilution technique that depends on reducing 

the quenching to a negligible factor by using a sufficiently small 

sample for the analysis. As the intensity of fluorescence measured 

in the procedure usually is weak, a sensitive fluorimeter is necessary. 

Also with such low levels of fluorescence contamination by airborne 

dust may be significant; rigid controls designed to minimize contamination are therefore desirable.

The second procedure involves the separation of uranium from 

interfering elements before estimation by the fluorescence method. 

This separation generally involves the extraction of uranyl nitrate 

with organic solvents after the addition of a salting agent. The distribution of uranyl nitrate depends both on the solvent employed and 

on the salting agent selected, and a particular procedure may lend 

itself to either batch or continuous extraction.

A batch extraction is employed using aluminum nitrate as the salting agent and ethyl acetate as the solvent. Aluminum nitrate was 

selected because moderate amounts of aluminum (about 50 mg) have 

shown no quenching action on the uranium-fluoride phosphors. 

Also aluminum effectively complexes phosphate, sulfate, and fluoride 

ions that normally interfere with the quantitative extraction of 

uranium. Ethyl acetate was chosen as the solvent because it is 

easily obtainable and presents relatively little fire hazard. At first 

it was thought that the ethyl acetate might hydrolyze to SOme extent 

and that the acetate ions formed could conceivably complex the 

Uranium and prevent its complete extraction. In practice, however, little if any ethyl acetate hydrolyzes and no interference of this 

kind results, but it is doubtful whether ethyl acetate can be used for

continuous extractions.

DISCUSSION AND PROCEDURE

The Sample (0.15 g) is completely decomposed by fusion with.

a sodium hydroxide-sodium tiMt mixture, This flux will decompose shales and phosphate rocks. After fusion the melt !s leacW

with water, acidified with nitric acid, and 7.5 ml Of nltriC atid 2 ai6 

added In excess. Silica d06S not separate out if the acid is added to

1 Price, Q. R., Ferretti, K. J., and Schwartz, S., 1945. The microfluorometric determination of uranium.' 

AECD 2282. 

3 Present practice is to employ 3.5 ml excess HNO» (part 1, extraction method).
VISUAL FLUORIMETRIC DETERMINATION OF URANIUM 45

the cool solution. Any hydrolytic precipitate that may form is not 

filtered off. The solution is then made up to 50 ml and a 5-ml aliquot 

is transferred to a test tube. To this are added 9.5 g of aluminum 

nitrate (enough to saturate 5 ml of solution) and 10 ml of ethyl acetate, and the mixture shaken for 30 seconds. After the layers have 

separated, about 8 ml of the ethyl acetate layer is drawn off and 

filtered through a dry filter paper. Five milliliters of the filtered 

ethyl acetate are removed by pipette, transferred to a clean platinum 

crucible, and evaporated off. The fluoride flux is then added to the 

crucible and the flux is melted for about 2 minutes. After cooling, 

the fluorescence is compared with a series of standards also contained 

in platinum crucibles. The standards are prepared from known 

amounts of a uranium solution transferred to platinum crucibles and 

finally heated with the fluoride flux in the same manner and for the 

same length of time as for the samples. To bring the flux in contact 

with any of the sample that may have crept up during the evaporation, it is necessary to play the melt around the sides of the crucible. 

It is preferable to prepare the standards in the same manner. Proper 

heating is an important factor in the results obtained. Too much 

heating, especially at an elevated temperature, will dissolve some 

platinum, which causes quenching; too little heating may also give 

low results because insufficient time has been allowed to incorporate 

the sample into the flux. With a little experience, the proper method 

of heating is easily determined. Each operator should make his own 

set of standards.

The fluoride flux used ha the procedure consists of 9 parts by weight 

of sodium fluoride, 45.5 parts by weight of sodium carbonate, and 

45.5 parts by weight of potassium carbonate, intimately ground and 

mixed. Standards made with this flux are kept in a desiccator and 

should be prepared daily.

The extraction of uranium nitrate by 10 ml of ethyl acetate according to the above procedure has given good quantitative recoveries 

of 0.15, 0.3, 0.45, 0.60, 0.75, 300, and 5,000 micrograms of uranium. 

The extraction data on a few other elements are described on pages 

47 and 48. For the concentration of thorium tested about 60 percent 

of the thorium is extracted.

The results of the analyses of a placer sample and a shale (table 1) 

using ethyl acetate extraction and colorimetric instead of fluorimetric 

estimation show the feasibility of batch extraction for colorimetric 

amounts.

A blank should be run on each bottle of aluminum nitrate to be 

used in the analysis. If the nitrate contains uranium, it may be 

purified by batch extraction with ether using the proportions 9.5 g
46 METHODS OF ANALYSIS, URANIUM AND THORIUM

of aluminum nitrate, 5 ml of 15 percent nitric acid and 10 ml of 

ether. It is then crystallized at room temperature after some of the

water has evaporated.

PROCEDURE

The final fluorimetric estimation is made in the range 0.075 to 0.75 

microgram of uranium. For ores containing 0.001 to 0.01 percent 

uranium, the uranium from a 7.5-mg sample is fused in the fluoride 

flux; for higher percentages of uranium a proportionately smaller 

sample is fused.

1. Grind about 2 g of 40-80 mesh sample in an agate mortar to a 

fine powder to insure that a representative sample will be taken for 

analysis.

2. Weigh 0.15 g of the sample and transfer'it to a clean 25-ml iron 

crucible. Roast if organic matter is present.

3. Add 1.5 g of NaOH (15 pellets) and about 0.1 g NaNO3 and 

fuse at the lowest possible temperature. The fusion should be as 

brief as possible to minimize the introduction of iron into the sample.

4. Allow the melt to cool. Add 15 ml of water and heat on the 

steam bath to disintegrate the melt.

5. Transfer the solution to a 100-ml beaker, scrubbing the crucible 

thoroughly.

6. Allow the solution to cool to about 30 C. Add HN03 dropwise to neutrality and then 7.5 ml in excess. 2 Any hydrolytic precipitate that forms is not filtered off.

7. Heat the solution just to boiling. Cool.

8. Transfer the solution to a 50-ml volumetric flask. Add water 

to make 50 ml and pipette a 5-ml aliquot into a 30-ml glass-stoppered 

test tube.

9. Add 9.5 g of A1(NO3) 3 -9H2O and dissolve the salt by heating 

over a flame. Mix the solution and cool under the tap. When a 

large number of Samples Ere run at One time, it is more convenient 

to place the test tubes in a beaker of boiling water to effect the SOlUtion of aluminum nitrate and in a beaker of cold water to cool the

solutions, 

10. Add 10 ml of ethyl acetate from a pipette, stopper the tube,

and shake for at least 60 seconds. Release the pressure and allow 

the layers to separate for about 5 minutes.

11. Pour Off abOUt 8 ml Of the ethyl acetate layer through a dry 

5.5-cm Whatman No.-42 filter paper fitted into a dry test tube.

12. By meanS Of ft Clean dry pipette transfer 5 ml of tKe filtered 

ethyl acetate to a clean 25-ml. platinum crucible. Both the filtratM

and aliquoting may be made with the volumetric filtering pipette 

(part 7).

'Present practice is to employ 3.5 ml excess HNOs (part 1, extraction method).
VISUAL FLUORIMETRIC DETERMINATION OF URANIUM 47

13. Place the crucible on 4 layers of water-soaked absorbent paper 

and set fire to the ethyl acetate with a lighted splinter held just above 

the solution.

14. Dry the residue on a steam bath. Add 3 g of the fluoride flux 

and heat over a low burner. After the flux melts, heat for 2 minutes 

playing the melt around the sides of the crucible to dissolve any 

sample that creptup during the evaporation. The temperature 

should be kept below 700 C. Allow the melt to cool and solidify.

15. View under ultraviolet light and match the fluorescence against 

a series of standards made to correspond to the following percentages 

of uranium based on a 7.5-mg sample: 0.000, 0.002, 0.004, 0.006, 

0.008, and 0.010. These contain, respectively, 0.00, 0.15, 0.30, 0.45, 

0.60, and 0.75 micrograms of uranium in 3 g of flux. For this work 

the source of ultraviolet light was the 110-volt, 60-cycle, Mineralight 

lamp. However, a long wavelength ultraviolet light (3650A) is preferable. Ultraviolet radiation may be dangerous to the eyes. Goggles 

transmitting 5200 to 6400A radiation should be worn when visual 

comparison is made.

The short wavelength lamp is a cold quartz mercury lamp, 90 

percent of its radiation is in the 2537A mercury line. The Corning 

red-purple Corex filter no. 9863 transmits the ultraviolet light and 

absorbs visible light.

ANALYTICAL RESULTS AND EXTRACTION BEHAVIOR 

OF OTHER ELEMENTS

Several representative samples were analyzed by the Geological 

Survey cupferron-colorimetric procedure and by the fluorescence procedure described in this paper. Two samples were also analyzed 

colorimetrically using the batch extraction of uranium with aluminum 

nitrate as the salting agent and ethyl acetate as the solvent. The 

results are shown in table 1.

Table 2 gives the results of fluorimetric analyses of a series of 

samples of shales and phosphates whose uranium content was not 

known to the two analysts. These results compare favorably with 

the results obtained by using the Geological Survey cupferron-colorimetric method.

To 5 ml of a 15 percent nitric acid solution containing the nitrate 

of the element under test, 9.5 g of aluminum nitrate were added and 

shaken 30 seconds with 10 ml of ethyl acetate. The ethyl acetate 

layer was drawn off and filtered and then tested quantitatively for 

the particular element. The results are given in table 3.
48

TABLE 1. Comparison of results of uranium determinations by three methods of

analysis

Sample

Phosphate rock __ 

Do--.. .... .

Do... 

Do 

Do. 

Silicate containing

Do 

Do.. .. .

Percentage uranium determined by 

Cupferron-colorimetric 

method

0.012 

.023

O99

.011

.017

.032

.0075

.0055

.002

Extraction-colorimetric 

method

Fluorimetric 

method

0.012 

.022 

.023 

.011 

.016

.032 

.007 

.005 

.002

Sample

Shale.. - ._ .

Do... 

Do... 

Do -

Do............

Zircon concentrate. 

Do-... 

Monazite. ". .....

Percentage uranium determined by 

Cupferron-colorimetric 

method

0.007

.007

.0025

.008

.009 

.12 

.019 

.09

.19

Extraction-colorimetric 

method

0.009 

.12

Fluorimetric 

method

0.007 

.007 

.002 

.008 

.009 

.1 

.02 

.09 

.2

TABLE 2. Comparison of results of uranium determinations obtained by fluorimetric 

and colorimetric procedures

Sample no.

1.. ...... .

2 

3....... .

4 ......

Percentage uranium determined by 

Fluorimetric method

(Analyst .4)

0.015 

.017 

.022 

.003

(Analyst B)

0.015 

.015 

.020 

.003

Cupferroncolorimetric 

method

0.012 

.014 

.020 

.003

Sample no.

5.-.. _ .

6... .........

7....... ..

Percentage uranium determined by 

Fluorimetric method

(Analyst^)

0.002 

.0085 

.020

(Analyst B)

0.002 

.008

Cupferroncolorimetric 

method

0.002 

.008 

.022

TABLE 3. Extraction of some other elements with ethyl acetate

Compound taken

ThOi........ ..... ....

ZrO,...... .........

ViOi... ..............

Amount 

(E)

0. 0025

.0025

.025

Amount ex- tracted with

10 ml ethyl

acetate (g)

0. 0015

(')

»<. 00001

Compound taken

FejOj.... .... 

Al (NOiMHiO......

Amount 

(g)

0.2

9.6

Amount extracted with 10 ml ethyl 

acetate (g)

0.00005

». 00004

1 Ethyl acetate layer was tested with phosphoric acid. No precipitate for zirconium phosphate formed 

after 2 days. 1 Recent experiments indicate that vanadium is partially extracted when larger volumes of ethyl acetate

are used.

* Determined as aluminum oxide (AliOa).
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 7. A VOLUMETRIC FILTERING PIPETTE

By F. S. GRIMALDI

During chemical analysis it is often necessary to niter a solution 

and later to take a measured aliquot of the filtrate for analysis. The 

volumetric filtering pipette (fig. 1) was designed to provide a tool 

whereby the filtration and aliquoting may be made in one step. It 

was designed specifically for use in the extraction procedure for the 

determination of uranium (part 6).

The volumetric filtering pipette consists of two parts:

1. The male part (fig. 2A) made of a standard taperedglass joint (the one shown is standard taper 7/25) is 

fused to a glass tube (fig. 2.Z?) calibrated to deliver a 

prescribed amount of solution. This constitutes 

the pipette proper.

2. The female part (fig. 2(7), or cap, also made of a 

standard tapered-glass joint, fits snugly over the 

male joint. This filtering cap contains the filtering 

 medium, such as absorbent cotton. The tip of the 

pipette proper is covered by the cotton plug in the 

cap as illustrated in figure 2.

A cotton plug or other suitable filtering medium is inserted in the 

cap, which is attached to the pipette proper, so that the tip is embedded in the cotton plug. The filtering pipette is inserted into the 

solution, and the solution is withdrawn by gentle suction at the 

mouth of the pipette. The solution is thus filtered and any desired 

amount may be delivered after removal of the cap.

This pipette has been used successfully to filter both gelatinous and 

crystalline precipitates.

49
50 METHODS OF ANALYSIS, URANIUM AND THORIUM

This simple apparatus, although designed primarily for laboratory 

procedure, should be useful also for a variety of chemical tests for 

use in the field. For such purposes, it could serve as either a filter 

or a pipette, or both. The constituent parts are easily obtainable, 

inexpensive, and should add little weight to portable field kits.

B

FIGURE 1. Volumetric filtering pipette. FIGURE 2. Details ot volumetric filtering pipottc.
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 8. A STUDY OF CRITICAL FACTORS IN THE "DIRECT' 

FLUORIMETRIC DETERMINATION OF URANIUM

By MARY H. FLETCHER

CONTENTS

Page 

Abstract_ _-_--_-___----_-__--_----__________---_-______-__-_____ 52

Introduction. _____________________________________________________ 52

Experimental data and discussion__________________________________ 53

Analytical procedure.______________________________________________ 61

New data on time-temperature study----_-_-_____---_-__-____--_-___- 65

ILLUSTRATIONS

PLATE 1. Assembly of Model II transmission fluorimeter______________ 62

2. Model II transmission fluorimeter________________________ 63

FIGURE 3. Effect of fusion conditions on fluorescence of blank samples... 57

4. Effect of fusion conditions on fluorescence of standard samples. 57

5. Effect of fusion conditions on sensitivity..__________________ 58

6. Equipment__________________________________________ 62

7. Effect of fusion conditions on fluorescence of standard samples

as shown in new data._________________________________ 66

TABLES

TABLE 1. Attack on platinum lid by flux as a function of fusion temperature. ._________________________________________________ 55

2. Time-temperature study for blanks.__._-___________-_-_-___ 56

3. Time-temperature study for standard samples..______________ 56

4. Effect of fusion conditions on sensitivity___-_---________-__ 56

5. Reproducibility of fluorescence of blanks heated in a small

furnace_ __-___________-__________-_____-___-_-----___ 60

6. Reproducibility of fluorescence of blanks heated in a large

furnace_ _ -__-_______--___-_-_____-_-_____-___-_-_---- 60

7.. Inadequacy of fusion mixture prepared by ball-milling._______ 61

8. Replicate analyses of standard shale sample GST-1.__________ 62

9.. Replicate analyses of standard shale sample GST-2___-___.___ 65

10. Comparison of results obtained by different methods of analysis

of northwestern phosphates._____________________________ 65

11. Determination of uranium by the "direct" method using

different aliquots.._____-_____-_____----__-_---.-------- 65

12. Time-ternperature study of standard samples containing 0.005

microgram of uraniuin______________--_-_---__-_--_---_- 67

13. Comparison of fluorescence readings for melts fused at 800 C

in different platinuinware--_______________-_-_-__---_---_ 67

NOTE. This report was issued as Trace Elements Inv. Eept. 130,1950.

51
52 METHODS OF ANALYSIS, URANIUM AND THORIUM

ABSTRACT

A study was made of some of the important factors in the "direct" fluorimetric determination of uranium in the range 0.0005 to 0.08 microgram, and a 

modified procedure based on these results is given. Detailed time-temperature 

studies showed that the sensitivity of the fluorescent method decreased rapidly 

when the fusion temperature was greater than 650 C, and that at temperatures 

above 650 C the sensitivity decreased with increased time of heating. Inhomogeneity of the carbonate fluoride flux led to erratic results.

Highly reproducible results were obtained by fusing at 650 C for 25 minutes, 

using a carbonate fluoride flux that had been fused and then ground. Phosphors 

prepared by this procedure are reproducible to about ±5 percent day after day, 

thus allowing the use of a permanent standard curve. Standard samples are 

unnecessary once the standard curve has been prepared.

INTRODUCTION

Many of the chemical laboratories that analyze large numbers 

of samples for traces of uranium use a "direct" fluorimetric method 

for many of the determinations. In the direct fluorimetric method 

the sample or sample aliquot is fused with sodium fluoride or an 

alkali carbonate fluoride mixture, and the fluorescence of the melt 

is measured. The use of Price's "dilution" technique l and the 

development 2 3 * of extremely sensitive fluorimeters (discussed in 

parts 11, 12, and 13) have eliminated almost entirely the necessity for 

chemical separations. Although the manipulative details and the 

equipment used in the different laboratories differ, the general method 

for the direct determination of uranium has been well established.

All the instruments referred to, and perhaps others, have greater 

sensitivity than can be used to full advantage. At present, the size

and reproducibility of the blanks set the lower sensitivity limit. 

The errors that occur in readings of replicate blanks or standards 

usually are greater than the instrumental error, which may be measured by replicate readings on a single blank or standard. Further 

improvement of instrumental sensitivity or precision should be 

secondary to the production of more reproducible phosphors and to

obtaining a fusion mixture tKat will,give lower blank readings.

In setting up a standard procedure for the direct determination of

uranium in this laboratory, a method was sought for phosphor preparation that was reproducible day after day, and one that would allow

for the duplication of the fluorescence to ±5 to 10 percent for melts 

of any given uranium content. Such a phosphor would make it

1 Price, O. R., Ferretti, R. J., and Schwartz, Samuel, 1945, The microfluorometrie determination of 

uranium: AECD 2282. 

» Pickel, O. B., 1946, AECD 2433. 

»Price, O. R., Ferretti, R. J., and Schwartz, Samuel, 1948, The design and construction of sensitive

fluorophotometers, part 1, principles: A.NL 4113.

< Smith, 8. B., and Neti, H. 0., 194C, Y-407.
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 53

unnecessary to fuse standards with each batch of unknowns. One 

standard curve could be prepared and used permanently with only 

infrequent checks, for example when a new batch of flux was prepared. A transmission fluorimeter (part 11) was chosen for the 

measurement of the fluorescence. This instrument is set to a "standard deflection" which is a measure of filter leakage; therefore, once 

the standard curve is prepared, standard samples of any kind are 

unnecessary.

Several investigators have reported the effects of different methods 

of heating on the fluorescence of fluoride melts. Some have pointed 

out the variations in results that occur when the fusions are made in 

oxidizing as contrasted to reducing atmospheres, 6 or at high temperatures as contrasted to lower temperatures,6 or in atmospheres of 

various gases.7 Others 8 9 have stated that fusions with a similar flux 

should not be made at temperatures greater than 750 C because of 

the solution of platinum at higher temperatures (part 6).

Early work in the laboratory indicated that temperature, period of 

fusion, and homogeneity of flux were the most important factors 

affecting the reproducibility of the method. It was thought that a 

homogeneous flux could be prepared by fusion of the ingredients, 

followed by grinding and mixing, and that furnace fusions at controlled temperatures for a standard length of time would give reproducible phosphors.

These ideas proved correct, and a satisfactory method has been 

found for the preparation of reproducible phosphors. Quenching by 

platinum dissolved from the fusion vessel by the flux is probably the 

chief cause for nonreproducibility in earlier work. Controlled lowtemperature fusions practically eliminate this error.

EXPERIMENTAL DATA AND DISCUSSION

Many substances were considered, and several mixtures were tested 

before the final choice of a fusion mixture was made. A one-component flux such as sodium fluoride should be ideal for homogeneity; 

however, this substance has a very high melting point, and if used 

alone adheres strongly to the platinum fusion vessel. Several different mixtures of sodium fluoride and sodium carbonate were tested, 

and either they had a tendency to stick to the fusion vessel or they 

gave discs that were too fragile. The three-component mixture used

» Grimes, W. R., and Clark, F. E., 1948, Clinton Eng. Works, Term. Eastman Corp., H. 1.740,10.

 Simpson, S. D., 1949, The photofluorometric determination of uranium: Nat. Research Council, Atomic 

Energy Project, Chalk River, Ontario, Canada; R. M. 0.14 [abstract no. 26] or no. 263/26 (paper presented 

at the London Conference).

' Price, G. R., Ferretti, R. J., and Schwartz, Samuel, 1947, ANL 4002 and addenda.

> Bartlett, T. W., and others, 1945, Fluorescent methods: Term. Eastman Corp., C-4.100.19, p. 9. 

 Clinton Eng. Works, Term. Eastman Corp., Div. of Chem. Research and Devel. Anal. Dlv. P. P. R. 

period ending July 1946, Doc. C.4.360.11, Ser. A, p. 38.
54 METHODS OF ANALYSIS, URANIUM AND THORIUM

by Grimaldi and Levine (personal communication) had the requisite 

physical characteristics. The composition of this flux is 9 parts of 

sodium fluoride, 45.5 parts of sodium carbonate, and 45.5 parts of 

potassium carbonate by weight. To remove any uncertainty concerning the uniformity of the fusion mixture, a large batch was prepared 

by fusing the ingredients in a platinum vessel, hand-grinding the cool 

melts in a mullite mortar, and thorouglily mixing the combined batches 

by rolling on a mixing cloth.

The melting point of this flux was determined by the standard 

method of making melting and cooling curves. The mixture started 

to melt at 575 C and was completely molten at 605 C. On cooling, 

the flux started to solidify at 605 C and seemed tO be completely 

solidified at 575 C. No sharp break was observed in either curve. 

The fusion was made in a J. L. Smith crucible heated in a small electric pot furnace. The temperatures were determined by measuring 

the voltage developed in a platinum-platinum+rhodium thermocouple placed in the molten material.

For the time-temperature studies, replicate blank samples and 

standard samples containing 0.005 microgram of uranium were fused 

with 1.5 g of flux in the platinum lids of 25-ml crucibles. The fusions 

were made at 800, 750, 700, 650, and 620 C for different intervals of 

time. Two to four replicates were made for each period at each 

temperature. The fusions were made in a small muffle furnace that 

accommodated two lids at a time; the melts were mixed by swirling 

about three times during the fusion period. The furnace temperature 

was controlled at the higher temperatures by manual operation of a

rheostat; for the tests made at 650 and 620 C the temperature was 

regulated with an automatic controller. When the lids were removed 

from the furnace, they were held by tongs until the melts crystallized.

They were then cooled in a desiccator for 30 minutes before the fluorescence was measured.

The groups of melts, fused at 800 C and at 750 C, each formed a 

graduated COlor Series When compared under white light. The melts 

of each group increased in the intensity of their yellow Color with the 

length of the fusion period ; those that were fused at 800 C were darker yellow than the corresponding melts fused at 750 c. For example, the

intensity of the yellow of a melt fused at 800 C for 3 minutes corresocmcUcl to that of a melt fUSed at 750 C for 10 minutes; and the fluorescence of these two pnospuors m*,, w«« ^^^.M... i^0 

meits that were fused for 5 to 10 minutes at 800 and 750 C showed a

decided murkineSS just before they solidified; however, when the 

meltS WOro retnvre<i from the lids in which they were fused, the lids 

were relatively clean. By way of contrast, 6Yen 40-mmute fUSlOHS 

at 650 C and less gave melts that appeared to be perfectly white but
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 55

the lids used for these fusions showed a dark stain. This stain 

increased with the length of the fusion and was very heavy after the 

20- and 40-minute fusions. At temperatures of 650 C and less, the 

platinum lid seemed to be attacked, but only a small part dissolved in 

the melt.

The degree of attack on the lid by the flux was determined for 

fusions made at different temperatures. Samples of a fusion mixture weighing 1.5 g each were fused for 10 minutes in the small furnace. Portions were fused at 650, 700, 750, and 800 C. Two were 

fused at 800 C and then re-fused for an additional 10 minutes at 

650 C. The melts were dissolved in a little water and hydrochloric 

acid, and the solutions evaporated to dryness. The residues were 

dissolved in water and analyzed for platinum by the stannous chloride 

colorimetric method. 10 The standards used for comparison contained 

1.5 g of fusion mixture treated in the same manner. The lids that 

were used for these fusions were boiled with (1 + 1) hydrochloric 

acid until the stain disappeared. The lids then were removed and 

the solutions evaporated to dryness. Platinum was determined on 

these residues by the same colorimetric method except that a new set 

of standards that contained no fusion mixture was used for comparison. The density measurements were made at 420 mju with a Beckman spectrophotometer.

The results of these analyses are given in table 1. The platinum 

content of the melts is a direct function of the fusion temperature.

The results of the time-temperature study have been summarized 

in graphs. Figure 3 shows the fluorescence of blanks plotted against 

total time in the furnace at different temperatures. Figure 4 shows 

the same for standard samples that contained 0.005 microgram of 

uranium. In figure 5 the data presented in figures 3 and 4 are combined and the sensitivity is plotted against total time in the furnace 

at different temperatures. Tables 2, 3, and 4 present the data from 

which these graphs were prepared.

TABLE 1. Attack on platinum lid by flux as a function of fusion temperature 

[10-minute fusion in small furnace]

Temperature of fusion (° C)

650.. 

700.. 

760. 

Micrograms of 

platinum found 

In melts

0 

33 

76

On lids '

156 

113 

148

Temperature of fusion (° C)

800. 

800' 

800 » 

Micrograms of 

platinum found 

In melts

155 

174 

174

On lids '

125 

218 

250

1 Soluble in hydrochloric acid.

3 Re-fused for an additional 10 minutes at 650 C.

" Sandell, E. B., 1944, Colorimetric determination of traces of metals, p. 358, New York, Interscience 

Publishers, Inc.
56 METHODS OF ANALYSIS, URANIUM AND THORIUM

TABLE 2. Time-temperature study for blanks 

[1.5 grams of flux]

Total time in furnace (minutes)

1. 

1H~ - - - - - -

2.. .......

2H 

3. 

4. 

5 

6. - .

7. 

10. 

16. ..................... ...................

20. 

40... 

Average readings-divisions on 0.02 scale

800 C

20.5 

18.0 

13.8

6.6

5.3

3.2

7500

16.8 

19.9 

17.6

13.5

8.5

6.1

7000

16.7 

20.9

20.6

18.0

14.1 

14.6

6500

-

15.2 

17.6 

18.8

20.7

19.1 

18.8 

18.9 

19.7

620 C

21.6 

21.2 

22.6 

23.6 

23.2 

23.1 

24.0 

26.1

TABLE 3. Time-temperature study for standard samples containing 0.005 microgram of uranium

[1.5 g of flux]

Average readings-divisions on 0.02 scale

1_ 

1H - 

2 _ 

ouc

3....... ... 

^. ................................ .-...-.. .

5. ........................................ .

6.. .-. - ~

7........ ... . 

10... -.. _ . 

15. _____ ... __ .. . .

20.......... ............... .......... ..

40... . 

8000

45.0

32.6

22.7

13.7

7.0

4.6

7500

41.7

46.7

43.2

33.1

20.6

13.3

700 C

42.9

47.0

44.5

38.7

32.6

31 0

6500

40.1

43.3

47.0

60.3

47.0

46.7

6200

'50.9

"50.8

'61.1

'51.9

'63.7

i co e

'52.8

1 Data calculated from readings on 0.05 scale.

TABLE i.-^-Effect of fusion conditions on sensitivity

Spread between blank and 0.005 microgram of uranium

(divisions on 0.02 scale)

1- 1H. ..... .. ...... 2. 

ol^J

3. _____________ . .

4------..-.. 5 ___________ I.:.::::::"::"

...... 

7. 

10. _____________ ... .......... 15.. ...

20....... . ...........................

4O __ __

800 O

24.5

14.6 

8.9

7.1

1. 7

""""l'.3

750 C

24.9

26.8

25.6

19.6

11.5

........ 

7000

a), 6 

26.1

23.9

20.7

"""¥5"

17.3

6500

24.9

25.7

OQ 0

*O. "

29.6

. 

97 Q

29.8

28,2

6200

00 1

29.6

28.3

30.5

Oft A

28.8

30.7
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 57

5 10 15 20 25 30

TOTAL TIME IN FURNACE (MINUTES) 

FIGURE 3. Effect of fusion conditions on fluorescence of blank samples.

35

UJ

_) 

<

t>

w

8 SO

d 

§

</>

o

tn

>

0 

. 9<« Ul CO

< 

O 

</>

uj 

u

z

U 

<J</)

UJK

o

3 o

" C

A nf^"

JP( "

i 

1 

\ 

' 

V N

1 X

T X\ *~ "*

! \

\ V- -

V ^750

\

\

^v. 800° C

"' ,.J

1

) 5 l(

620° (? > G *

650_°C;

, 700 °C * _ -GJ

. ___ Blo/lL^ 650° <

C

i

I

) 15 Z

)

\ _ __ _ __ _ _ _ _

i

0 25 3

<

0.005 microgrom of

uranium 

1.5 grams of flux

_ _ __ _ _ __ _

i

0 35 4

>

0

TOTAL TIME IN FURNACE (MINUTES) 

FIGURE 4. Effect of fusion conditions on fluorescence of standard samples.

268681 54-
AND THORIUM

TOTAL TIME IN FURNACE (MINUTES)

: :Iauhi lo sorwos'jio.iiJl ITO yioKibnoo noiaiO to iasliH .& 3;rj9.<r>J

FIGURE 5. Effect of fusion conditions on sensitivity.

40

\ ' ' I* Tfhese graphs and tables show |the effects of uncontrolled hejathjg

""fTl"""" . <,' 

fusions. [The 

J; _ _^ 

fluorescence 

1 61

or^wittiout j&d^d^^^aiuiiiELiSj af- 111* T-». 4- -fl' *J

fected trenie'ndously by "the" conditions -of--the- fusion. The ;;fluoresfusion when the temperature'is greater ^-t^aiii ,650 C. For! very 

shott fusions (that) is, just long enough to melt the flux ap.d ;quick|y

mix Jt) *th.6-flnOXescence »at=aU~teinip.eraturfis^_neajLJlie-,:hia5iriium; 1 I I 1 ' / '"" [41 

^nq. for low^-jiempelrature fusions, itLe8%o,rgsCenC6 JS tJhs^anife fj)r |3J

periods of fusion provided the ImaxuTaum'liaV been .reached. ; Tn;e 

graphs indicate tha,t the best fusion conditions are''a" temjjerature i^f 

^50| C for a period of at least 10 ipinutes in the furnace ^ed fot th|s

^=$iis furfiace is -smaU and the ^hoHnoeoupl©- not-©B i«'se4j-as-a r|-

sult, it gives exc^l|ent.,Yres]pomse to :the conitroller. The" total variation from tlj&.desirjd $e^ the

furnace cooled when the door was'opened, it Heated up again almost

immediately. This small furnace was ideal for a study where careful temperature control was the principal consideration, but a larger
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 59

furnace is necessary for analytical purposes when large numbers of 

samples must be handled.

The best conditions for fusion in a large furnace are harder to define than are those for a smaller furnace. In a large furnace, there 

is usually a large temperature gradient from the front to the back of 

the furnace. There is also an appreciable lag which results in a lower 

or higher temperature than that at which the controller is set. When 

the door is opened to insert samples or to agitate them, the furnace 

cools and takes much longer to heat up again than a small one. Therefore, the temperature conditions within each furnace should be determined. A controller setting should be chosen that will not allow the 

temperature to rise above 650 C. Any part of the furnace that is 

always cooler than 605 C cannot be used.

The temperature controller for the large furnace used in this 

laboratory was set at 650 C, and 10 lids, on two racks in rows of 5 

each, were placed in the furnace at one time. The front one-third 

section of the furnace was too cool to fuse the samples and could not 

be used. The melts were mixed by shaking the rack three tunes 

during the fusion (the melts usually solidified at the end of the period 

of shaking). A period of 15 to 25 minutes was required to obtain 

reproducible maximum fluorescence in the melts. The 25-minute 

period finally was adopted as the standard fusion tune although 

some of the data presented were obtained at the shorter period.

Later, the furnace chamber was tested with a National Bureau of 

Standards chromel-alumel thermocouple used in conjunction with a 

potentiometer. The temperature at the position of the back lids 

ranged from 600 to 630 C, and at the position of the front lids from 

585 to 610 C. About 7 minutes were required to fuse the samples 

jj|ter they were inserted in the furnace; whereas, only \% minutes at 

 650 C and 3 minutes at 620 C were required in the small furnace. 

'The unexpectedly low temperatures in the large furnace and the consequent longer fusion time made necessary the 25-minute fusion 

perio4,r6quir >dito Qtytaift Reproducible fluorescence in the melts.

.More .efecient^tempefjature control results in better reproduction silt hlmjwoj j)»Jo?)TiT}*feii>Y.' uiJ&jMi um/>:-,. *\ ^%,%?/refc;W ^ltojB}^IJ%!S5^^m^ ^e wide vana-

<mr#tefc<fj ffite*^iffl^ff&% to^^ggm^W^0* the fluorescence was < y^§l.lr withinr!liolerable liimtSi. rable ; 5 ^giyes^upresonrreplicatej blank samples fused in the small lurnace. .jtfriJOfcTf fit; A>liT(p «/ywuity>iqr;L,-! ttinTTJ/iJan.v/ :>.;)>luna '

i mm^. The average, deviation from the mean is 0.6 division on the 0.02.scale ilimaubo'iip/l \ nmsi AT/*.ovi;a * /« yoRxiim ml m ymu,lk»oj <)/!) _?: : , 

for.stheT small furnace and 1.2 divisions, for the large furnace. [One »mi;1 *?il .y.isw riTffi m bfHuqfriq xofi'toi Ivmisjao yuPfron jbmoj) R>la . f

IJifiiJIiul <)iiT jioifcL'T v.d ');nsjq:nq itiilt moit

R bfnli/pm Jfiii) H<umjf jnri ,o8n1 ol Jmte Muow xutt lio
60 METHODS OF ANALYSIS, URANIUM AND THORIUM

division on the 0.02 scale was equivalent to 0.000144 microgram of 

uranium.

Tests by Norma Guttag (personal communication) of this laboratory 

have shown that careful fusions over a Meker burner give results 

comparable to those obtained in the small furnace. The fusions over 

a burner were made at the minimum temperature required to melt 

the flux. The molten material was constantly agitated for about 1 

minute. This procedure is quicker than furnace fusions, but demands 

that overheating be prevented. Analyses of several melts fused in 

this manner showed 3 to 10 micrograms of platinum.

TABLE 5. Reproducibility of fluorescence of blanks heated in a small furnace 

[Fusions made at 650 C for 5 minutes]

Sample no.

1 _ ..................

2...... ... ... ... ... ...

3.. ...................

4 ... . ... ..............

Scale reading 

(divisions on 

0.02 scale)

15.5

15.1

1C.O

16.0

1C f\

16.5

Deviation 

from mean 

(divisions on 

0.02 scale)

0.8

1.2

.3

.3

.2

Sample no.

7.. ... ... ....

8.. . 

9_. 

10.... - 

Scale reading 

(divisions on 

0.02 scale)

17.7

15.9

16.8

17.0

16.3

Deviation 

from mean 

(divisions on 

0.02 scale)

1.4

.4

.5

.7

.6

^E 6. Reproducibility of fluorescence of blanks heated in a large furnace 

[Controller set for 650 0; actual temperature fluctuated from 585 to 630 0. Period of fusion: 15 minutes]

Sample no.

1. ....... ..... ..... ...

2... .... ....... 

3.. ... ... ..... ... .

4..... .......... 

5..... .... ..... ... .

Scale reading 

(divisions on 

0.02 scale)

18.0

18.4 

20.2

18.7

22.1

91 Q

Deviation 

from mean 

(divisions on 0.02 scale)

1.7

1. 0

.5

1.0

2.4

2.2

Sample no.

7.. _ .. .. 

9.. .... . 

10... 

Mean........ 

Scale reading 

(divisions on 

0.02 scale)

19.0

18.6

20.7

19.7

Deviation 

from mean 

(divisions on 

0.02 scale)

0.7

1.1

1.0

1.2

The best fusion conditions for the preparation of the phosphors

having been determined, attention again was directed towards tu6

fusion mixture. Several duplicate blank samples of flux, which was

prepared by mixing the components in a ball mill without priOf fusion, 

were fused in the small furnace and their fluorescence measured to 

determine whether this simpler means co^id i>e use<i for preparing the 

flux. The readings obtained, the time required to melt the mixture,

and the total time in the furnace are given in table 7. ReprOO-UClDlS 

bi,xixks could not be obtained for fluX prepared in this way. Its fusibility also was different from that prop*-* ^r * 4~- ^ t 

variety of flux would start to fuse, but lumps tnat required ft
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 61

length of tune to melt usually were present. Sometimes as much as 

10 minutes were necessary to obtain complete fusion. Furthermore, 

many air bubbles formed next to the lid, and it was virtually impossible 

to get rid of them. In contrast to this, the mixture prepared by fusion 

always melted in about the same length of time (1 to 1% minutes at 

650 C); moreover, no lumps and scarcely any air bubbles were present. 

The details of the method finally adopted for the preparation of 

the fusion mixture follow:

Heat a mixture of 9 g NaF, 45.5 g of NaaC03) and 45.5 g of KaCOs in a large 

platinum dish in a furnace at 650 C for 15 to 20 minutes or until most of 

the material has fused. Complete the fusion over a Meker burner and 

swirl the melt until it is well mixed. Fuse as many 100-g lots of the mixture 

as desired. Then break up the cakes in a large mortar with a pestle until 

all of the fused material will pass through a 5-mesh screen. Place the 

lumps of flux in a dry warm ball mill, and tumble it for about 3 hours or 

until the mixture will pass through a 65-mesh screen. Remove the pebbles 

and again tumble in the ball mill for several hours. Store the stock in a 

large tight bottle. Transfer to smaller bottles as required for use. The 

mixture is hygroscopic in damp weather; consequently, when not in use, 

the containers must be kept tightly closed.

TABLE 7. Inadequacy of fusion mixture prepared by ball-milling 

[Fusions made in small furnace at 650 0 blank samples]

Sample no.

1..... ..

2..... ..... ...

3 ... ..... ..

4..... ..

5....... ...

Time 

required 

to melt 

(minutes)

3-4

3-4

3-4

10

8

Total time 

in furnace 

(minutes)

5

6

6

10.5

10.5

Reading 

(divisions 

on 0.02 

scale)

42.0

39.2

46.0

37.8

C)

Sample no.

6...-.-.....-

7..... ........

8.. ..-.-.-

9..._...-..._-

10.-.. .-..-

Time 

required 

to melt 

(minutes)

8

6

6

10

8

Total time 

in furnace 

(minutes)

10.6

10.5

10.6

10.5

10.5

Beading 

(divisions 

on 0.02 

scale)

(')

40.2

41.8

41.2

34.6

1 Off scale 36.1 on 0.05 scale. 

1 Off scale 23.0 on 0.05 scale.

ANALYTICAL PROCEDURE

The chief differences in the analytical procedure adopted by this 

laboratory and that used elsewhere are (1) the use of a transmission 

fluorimeter for the measurement of the fluorescence of the melts; 

(2) the use of controlled low-temperature fusions with the consequent 

elimination of standard samples.

Most other laboratories fuse about six standards and several blanks 

along with the samples for each fusion operation, and prepare a new 

curve for each set of samples fused.
62

\\\

 15 &

FIGUEE 6. Equipment.

The equipment used here is shown in plates 1 and 2 and figure 6. 

Plates 1 and 2 are photographs of the Model II transmission fluorimeter and d-c amplifier described in part 11 which were used for the WOrk 

described in this report. A Model V has now been built and is described 

in part 12, Figure 6 (A) shows the stainless steel racks that hold 10 

lids each. The lids are placed On these racks, the sample solutions 

pipetted onto the lids and dried in place on the racks. Figure 6 (D) 

shows chromel racks made from furnace-heating elements that are

used to hold the lids in the furnace during the fusion period. Figure

6 (<7) shows a transite plate with attached chromel rods plftCed Ott ttl6 

bottom Of the furnace tO serve as a support for the racks and samplea

during fusion. The Sample Solutions are transferred to the lids with 

graduated 0.2-ml pipettes. The platinum lids are irom 2o-wl 6TUClDl69i 

For the determination of the uranium in any sample, a small 

amount of the sample was weighed onto the lid, or a small amount of 

the Sample solution was pipetted onto the lid. When liquid, the sample 

was a^iea vnxci^ a.n infrared lamp or on a hotplate, and ignited

briefly. For both SOlldS and liquM»; 1.0 g o* ,^_ ^ 

added to the lid. The lids were transferred to the ckromel imS aflQ 

placed hi the furnace, which was set for 650 C; the samples were
GEOLOGICAL SURVEY 

ASSEMBLY OF MODEL II TRANSMISSION FLUORIMETER. A, fluorimeter; B, ph

E, voltage regulator; F, d-c amplifier; C, power source
GEOLOGICAL SURVEY 

MODEL II TRANSMISSION FLUOKIMETER. A, fluorimclcr; /(, phototube; C, ullruviolc
CRITICAL FACTORS IN THE

allowed to remain in the furnace for 25' iniii

they were mixed three times by shaking'the

end of 25 minutes the racks and lids were

The lids were placed in a desiccator and

after this period the fluorescence of the melts was measured1 .' r>

The size of the sample used for the final determination, and the 

methods of preparation of the sample solution are flexible and are 

determined by the nature of the sample and the quantity available. 

For average samples, the final aliquot was chosen to contain 0.001 to 

0.08 microgram of uranium, and usually represented 50 micrograms 

of sample although much smaller and much larger samples have been 

used successfully.

When the amount of sample is limited, the uranium content low, 

and the amount of quenchers negligible, the solid sample can be used 

directly. For example, with plant-ash samples that contain from a 

few hundredths of a part per million to a few parts per million of 

uranium and only small amounts of quenching elements, 5 mg of the 

solid sample are fused directly. When the sample is readily soluble 

in acid, 50 mg are weighed into a flask, 100 ml of 18 percent nitric 

acid measured into the flask, the flask covered with a watch glass and 

heated until it just boils. It is then cooled and a 50-microgram 

(0.10-ml) aliquot is pipetted onto the lid, and the determination 

continued as outlined. Samples not readily soluble in acid usually 

are decomposed by fusion with a mixture of sodium carbonate and 

sodium borate (4+1). This flux has the advantage of keeping silica 

in solution. For decomposition with the carbonate borax flux, 10 

to 50 mg of the sample are weighed into a small platinum crucible and 

fused with 500 mg of the flux. The crucible then is placed in a 100-ml 

beaker which contains 30 ml of 30 percent hydrochloric acid, and the 

beaker is placed on a hotplate for a few minutes. The fusion melt 

dissolves in about 3 minutes to give a clear solution. When the melt 

is completely dissolved, the crucible is removed from the beaker and 

rinsed with water. The solution is transferred to a 100-ml volumetric 

flask and diluted to volume. (Further dilutions of this solution are 

made if the percentage of uranium in the sample is greater than about 

0.1.) A 0.1-ml aliquot then is taken for the determination. Hydrochloric acid instead of nitric acid was used to prepare these sample 

solutions because there is danger of attack on the platinum by sodium 

nitrate and because less creeping of the borate residue occurred with 

hydrochloric acid. An aliquot of 0.1 ml of sample solution was chosen 

because it evaporates quickly and the residue is confined to a small 

spot; thus the flux is always in contact with the sample during fusion.

The lids used for the determination are cleaned by acid washing. 

The melts are removed, and the lids boiled for a short time in 1:1
64 METHODS OF ANALYSIS, URANIUM AND THORIUM

hydrochloric acid to which a few milliliters of hydrofluoric acid have 

been added. The acid then is drained off, the lids rinsed with water, 

and boiled once or twice again with 1 : 1 hydrochloric acid. They are 

then rinsed well with distilled water, and dried over a bunsen burner.

Results of determinations carried out by this method are given in 

tables 8, 9, 10, and 11. In table 8 the results of replicate analyses 

on standard shale sample GST-1 are given. The average amount of 

uranium found was 0.0087 percent U with an average deviation from 

the mean of 0.00018 percent U. The average amount found by six 

laboratories was 0.0086 percent U± 0.00017 percent U. Table 9 

shows the results on the standard shale sample GST-2. The percent 

uranium found was 0.0127 percent U with an average deviation from 

the mean of 0.00038 percent U, whereas the average value from six 

laboratories was 0.0123 percent U± 0.00008 percent U. Table 10 

gives comparative determinations of uranium by the direct method, 

by the extraction procedure (see part 6), and by radiometric count. 

Each result represents a single determination. The correlation is 

good. Table 11 shows comparative results for determinations by 

the direct method using 100- and 20-microgram aliquots. Each 

value again corresponds to a single determination, and the results 

agree.

The method as outlined has sufficient sensitivity and accuracy to 

determine a few thousandths of a percent of uranium in a 0.02-mg 

sample. Through the use of small aliquots, quenching from foreign 

ions is reduced to a minimum, and chemical separations generally 

are unnecessary. Low-temperature fusions eliminate platinum quenching, Standards of any kind are unnecessary once the standard curve 

has been prepared. The method is especially useful where the amount 

of material is small, and it is invaluable where the sample is small 

and the uranium content is low.

TABLE 8. Replicate analyses of standard shale sample GST-1. 1 Uranium

0.0086 ±0.00017 percent

[100-mlerogram aliquots of sample]

Replicate no.

1...... __ . __ . __ ...

2........ _ ..........

3. _____ - ....

4 _____________

5...... 

7 _______________

Uranium

(mlcrograms

and percent)

0.0085

.0085

.0088

.0088

.0088

.0088

.0091

Deviation

(rnicrogramg

and percent)

fl flflfl9

finno

0001

.0001

,0001

.0004

«.* -.. .

0

g

12 ....................

Uranium 

^found^

and percent)

0.0086

.0081

(\r\QQ

.0088

.0087

Deviation 

from mean

and percent)

0,0001

.0006

ftftm

nftfti

.00018

i See part 11, table 5.
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 65

TABLE 9. Replicate analyses of standard shale sample GST-%.

0.0128±0.00008 percent

[100-microgram aliquots of sample]

Uranium content

Replicate no.

1... ...... .........

2

3.. ...................

Uranium 

found 

(mlcrograms 

and percent)

0.0133

.0128

.0128

Deviation 

from mean 

(micrograms 

and percent)

0.0006 nnni

.0001

Replicate no.

4.. ....... ............

Mean ..........

Uranium 

found 

(micrograms 

and percent)

0. 0120

.0127

Deviation 

from mean 

(micrograms 

and percent)

0. 0007

.00038

TABLE 10. Comparison of results obtained by different methods of analysis of

northwestern phosphates

Sample no.

1.. ..........

2.............

3.-......-.-.

4.............

5.............

Percent uranium found

"Direct" 

metbod, 100-microgram 

aliquot

0.009 

.008 

.010 

.010 

.007

Extraction, 3.6-milli. 

gram 

aliquot

0.010 

.007 

.008 

.010 

.007

Radiometric 

count

0.011 

.009 

.009 

.011 

.008

Sample no.

6.. ........

7 ....

8... .......

9.. ........

10............

Percent uranium found

"Direct" 

method, 100-microgram 

aliquot

0.004 

.013 

.011 

.008 

.010

Extraction, 3.6-milligram 

aliquot

0.004 

.013 

.010 

.008 

.008

Radiometric 

count

0.006 

.013 

.013 

.008 

.010

TABLE 11. Determination of uranium by the ''direct" method using different aliquots 

[Samples 1 through 12 are Florida phosphates; samples 13 through 20 are northwestern phosphates]

Sample no.

1. .. ..................

2.. .................. .

3.. .................. .

4.. ............... ....

5.. ................ ...

6........ .......

7....... ..... ... ...

8...... .... .... . ...

9.. ...................

10.. ..................

Percent uranium found

100-microgram aliquot

0.023 

.005 

.012 

.009 

.012 

.010 

.010 

.007 

.016 

.006

20-microgram aliquot

0.022 

.007 

.015 

.008 

.013 

.010 

.010 

.011 

.015 

.006

Sample no.

11.. .. ................

12.. ............ ......

13.. .............. ....

14.. ........... .......

15.. ................ ..

16.. ......... .........

17.. ............... ...

18.. ...... ....... .....

19... .................

20... .-.. -..-.-..-

Percent uranium found

100-microgram aliquot

0.013 

.017 

.013 

.008 

.010 

.013 

.009 

.013 

.006 

.013

20-microgram aliquot

0.014 

.019 

.013 

.008 

.007 

.012 

.009 

.014 

.006 

.013

NEW DATA ON TIME-TEMPERATURE STUDY

The time-temperature study, figure 4 and table 3, was repeated 

3 years after the original work. The standard (May) dish with 2.0 g 

of flux was used in this new study because these dishes are now in 

regular use in this Geological Survey laboratory (part 13). Otherwise the conditions of the tests were identical with those of the 

original work. As before, the fluorescence of the carbonate fluoride 

melts varied with the temperature and period of heating, and the 

degree of quenching depended upon the amount of platinum dissolved 

from the fusion vessel.
 fT-o 2;Qj cgrams .of.flu

! t:IO. May dishj~.-_._-...-..e 

5819 ph6f6fabe.:6'

-cnoim-OS 

jo.rpilii rain? ! toupil. 1 'ioxjpitn mcig i ioupila meig

-FiGT7BE-7>HEffect-of fusion-conditions-on-fluorescenceof-standard-samples-as^lown-Iii.new-data..

I SIO.O L -............ .....................U H SSO/J CSO.O.

711)^ ' 2 r. I \ty &rso n^w^data, piieseiited'lier^in igure 7 and table ..I';?!,'.-.. '_", ^-^r-^-=--ll^.W _,__. iqro.., _,

of fusions was repeated ^using 'jtlie crucitl^lids 

. .m, .£,, ..rJf!!% , i>% i earlier. investigatipiL _AccOTdingly:,_tne .series ^tused - a_t _

run again in the original lids with 1.5 g of flux. Less quenching

and? analysis --M the;) rn 

eonfe^pondiiigjnielib ^

,of

;.vLi lo isj^i}H&>.^ioij'<i oiii ,'i'io'itic. HA .>Iiovf l^i^r-u-jc;

iffeM^

the series. .loaaov noiau't yilj iuoi'1
CRITICAL FACTORS IN THE "DIRECT" FLUORIMETRIC METHOD 67

TABLE 12. Time-temperature study of standard samples containing 0.005 

microgram of uranium

[Fluorescence readings on 0.02 scale with ROA 6819 multiplier phototube]

Total 

time in 

furnace (minutes)

1.... .

ifc 

2........

2H- ~

3........

4.... .

5.. ...

6.... .

7.... .

10... .

15.......

Standard dishes and 2.0 g'of flux

620 0

Fluorescence (divisions)

42.0 

42.5 

45.5 

48.2 

48.2 

52.2

Pt 

micrograms

4 

6 

9 

11 

9 

16

650 0

Fluorescence 

(divisions)

36.0 

41.5 

45.4 

47.0

49.2 

47.0

Pt 

micrograms

COOOOO h-> 

'16 

'23

700 O

Fluorescence (divisions)

46.0 

49.5

49.1

47.8

45.0

Pt micrograms

16 

7

10

12

40

750 0

Fluorescence (divisions)

40.0 

46.1 

44.2

41.0

30.0

27.4

Pt 

micrograms

6 

7 

UO

»21

»35

172

800 0

Fluorescence 

(divisions)

43.0 

40.8 

37.8

31.2

25.0

22.2

Pt 

micrograms

5 

10 

21

34

64

82

Crucible lids 

1.5 g flux

800 0

Fluorescence (divisions)

45.0 

40.0 

36.8

25.0

22.8

19.1

Pt micrograms

7 

8 

13

24

66

74.0

1 Fusion in new May dishes.

TABLE 13. Comparison of fluorescence readings for melts fused at 800 C in 

different platinumware

[Readings on 0.02 scale with RCA 1P21 photomultiplier tube]

Total time in 

furnace (minutes)

1.........-. 

1J4.. ... ... ... ...

2..... ..............

Crucible lids

Original 

study

45.0 

32.6 

22.7

New 

study

51.0 

48.0 

43.0

Standard 

dish new 

study

39.5 

39.5 

35.0

Total time in 

furnace (minutes)

3.........-...... 

6...................

 10......... ........ -

Crucible lids

Original

study

13.7 

7.0 

4.5

New 

study

31.0 

27.5 

25.0

Standard 

dish new 

studjr.

<

s 30TO 

A 24.0 

32,0

 SBeside the differences already discussed, examination of fi;ure~S 

shows, as would be expected, that the rate of quenching is j;reai^r 

when a smaller amount of flux is used. The amounts of plt.tinuia 

hi the melts in the new tests were about the same for melts fi sed th 

lids and dishes under corresponding conditions. Whenever differences in platinum content did occur, there was a little mo£e 

platinum present in the melts fused in dishes. Hi

When the original study was-made, the lids used for the :usions 

were almost new; they have now been used continuously for 3 years. 

The continuous use and repeated cleanings of these lids have p^oQably 

left the vessels less susceptible to attack. This seems to be proved 

by the fact that analysis of the new melts shows only about half as

11. n * i ' i -i .LI >t»B!il .a ajjnojp much platinum in them as found in melts used in the original study.

It is possible that the composition of the platinum in the standard 

dishes is different from that in the lids because the age of these dishes 

made no significant difference in the results obtained. Some of the
68 METHODS OF ANALYSIS, URANIUM AND THORIUM

dishes used hi these tests were new whereas others have been used 

constantly for about 2 years.

These new data are presented not as a correction to the original 

study but rather to point out the differences in fluorescence that 

may occur from time to time even though identical fusion conditions 

are used. This indicates that such factors as the condition, age, and 

composition of the platinumware determine to a large extent the 

amount of platinum going into solution in the melts. The amount 

of platinum in the melts determines the amount of quenching that 

occurs and consequently the intensity of fluorescence.

Temperature of fusion 800 ° C

IP2I phototubeBaird filters

Instrumental' sensitivity comparable 

for all three curves

Lids, 1.5 g flux] New dofo 

Dishes, 2 g flux]

Lids , 1.5 

Original data

5 10 15 

Total time in furnace (minutes)

Effect effusion time and type of platffliUDware on p

20
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 9. A DIRECT FLUORIMETRIC METHOD FOR THE 

DETERMINATION OF SMALL AMOUNTS OF URANIUM 

IN THE FIELD AND LABORATORY

By F. S. GRIMALDI, F. N. WARD, and RUTH KREHER FUYAT

CONTENTS

Page

Abstract_______.________..________-..._______ 69

Introduction----_.--___---_____.___----_--___.-_-_-__-._-__----_-_ 70

Discussion of the method_._.___________-_-__----._--__----_-- 70

Procedure...___.______________________________________________ 71

Results of analyses________________________________________________ 72

Experiments._______________ ____________.____-_----___-_ 74

TABLES

TABLE 1. Fluorimetric uranium analyses of Florida phosphate samples;

comparison of direct and extraction methods ____________ 72

2. Fluorimetric uranium analyses of northwestern phosphate samples; comparison of direct and extraction methods._______ 73

3. Fluorimetric uranium analyses of black shale samples; comparison of direct and extraction methods.______-___-_---_--_-_ 73

4. Fluorimetric uranium analyses of carnotite samples of the 

Colorado Plateaus; comparison of direct and extraction 

methods_____.____-.______- ________ _______ 74

5. Determination of uranium, in percent, to show homogeneity of

two samples containing segregated uranium minerals.___.__- 75

6. Effect of sample weight in the direct method.._______________ 75

7. Equivalent fluorescence of elements other than uranium.______ 75

ABSTRACT

This paper describes a quantitative fluorimetric method to determine small 

amounts of uranium (0.001 percent to 0.01 percent on a 3-mg sample) which is 

useful for field and for laboratory screening. A small solid sample is fused with 

a fluoride flux, and the fluorescence of the uranium melt is measured photometrically.

The method has been tested on a large number of phosphate rocks, shales, and 

carnotite-bearing deposits. The results are sufficiently accurate to warrant use 

of the method for screening purposes.

NOTE. This report was issued as Trace Elements Inv. Kept. 98 and AEOD 2825,1946.
70 METHODS OF ANALYSIS, URANIUM AND THORIUM

INTRODUCTION

The methods most commonly used for the field estimation of small 

amounts (from 0.001 to 0.01 percent) of uranium are purely physical. 

The most important technique is a radiometric method using an 

instrument such as a portable Geiger counter. As radioactivity 

measurements do not discriminate between the radioactivity associated with uranium and that due to other elements such as thorium 

and potassium, it is highly desirable to supplement this method with 

an independent technique specific for uranium.

Field tests based on the fluorescence of sodium fluoride uranium 

phosphors have been used; these methods are qualitative in nature 

and have not been used for the quantitative determination of small 

amounts of uranium.

The simplest method for the analysis of uranium is to fuse a sample 

of the rock directly with one of the standard fluoride fluxes and to 

measure the fluorescence intensity of the resulting melt. This procedure was applied to shales, to other rocks high in silica, and to 

phosphate rocks from different localities. The reliability of the results obtained by this method was surprisingly good and better than 

we had anticipated. Although quenching of the uranium fluorescence 

occurred in many samples, it did not impair seriously the utility of 

the method for screening purposes. The method should be especially 

useful either in the field or laboratory for the rapid selection of samples 

that deserve more refined analyses.

In the laboratory the fluorescence is measured with a Modified 

Model R fluorimeter described by Fletcher and May in part 10.

This instrument may also be used in the field provided an outlet of 

110 volts a-c is available. Work is hi progress to develop a small 

portable battery-powered Unit SO that the instrument will be completely self-contained and independent of an external power 80111*66, 

After this report was issued to the Atomic Energy Commission, a 

battery-powered fluorimeter was developed by Irving May and Mary 

Fletcter, a,^d is described in part 13 of this bulletins.

DISCUSSION OF THE METHOD

The procedure involves a direct fusion of 3.0 mg Of Sample With 

3 g of flux in a platinum container. This size sample was selected for the Mowing reaso^-.

1. It may be conveniently weigW in the uGld Wltu ft 

(5-mg capacity) balance.
itE i malerials

ur uiil OK!!

3. This ratio of rock sample to flux was the 

 t$$M&fom^ ^u^neli^ 

in the sample. HWttYOCAKA. riO

With shales and phosphate rocksrground to 100 mesh, a 3.0-mg 

§&mplecV'a^'^jpre^enl'alitje!^ ^Mf^^c'oii'cRisio'h^ B is^'Was%d%n>Mhe'rafact

^lat^^uWWifto^Fto ^l^yiiu^)^

^^ttfc^1XW.l«ft^

without obtaining any spurio

suits on these samplesiwithvtho'se^obtadned-on^the original 100 mesh 

materialT Thes(e results are consistent-with^the fact -that no discrete 

Ijfitotefflft tas been found iij p^Hffir^|f or shales and that 

-uranium-occurs I in a fifl^^lssemihated- state-in-these saffiplM18 For 

^bntaui segregated! i uf^nljmT. ^Mejttls __a satisfactory 

to grind_a representa%e 1-g sample |to a powder inj| 

iBaprtar lbj$fpre Withdrawing the^;.3jOr|^g samD^Jior analyses- (see- -pv 74

IJ-n;Sevefja|{ndem Jntff;hBV r;been;J|f»®.ed as ffifterfering;m;_the--fluori| 

^etric procedure :by.;yirtTOjpf;;th|ir| $jjm fluor||cence!inj[\ioride^meltsj 

fjjhese, a|i°well as:-severai:pther4J i^e teste^to determine-^^the - 

Ability o|^mter^renc_e:ija::the.:

of the elf&ients ;teste(l;;slip_we^d;-|,iii^!j;fluores|C^!ice. jThese--results--ar

present 

A few

table7

^by^thxB^iirect-nle^HloJd gave !Ji|gh values-for--uramiinj| 

For exani^le, ti;e:Tes"u]ibs_7pn;:Fi^ri^||;phosi!>^ samples"2_8;;and 3Q| 

table 1, were sira^ca_ntl.y;i^ghe|' tl|.£&i thos'e^btamed- by;-extractioEL|

fluorimetric and radiometric- an...^«:

...OH | RJt0 . H03. icr*. .................... .............p

o;;

Rfli). ,,18

1. Grind sample to -^100 mesh-'and-mix.^

2. Weigh out 8.0 mg of sample and transfer to a 25-ml platinum 

crucible.

3. Burn off organic matter if present.

4. Add 3 g of fluoride flux (made by grinding together 9 g NaF, 

45.5 g Na2C03 , 45.5 g K2C03).
72 METHODS OF ANALYSIS, URANIUM AND THORIUM

5. Heat for several minutes over an open flame, swirling the contents 

of the crucible frequently until the sample is completely decomposed. 

Important: Use the lowest possible temperature at which the flux 

remains fluid. Cool.

6. Measure the fluorescence intensity of the melt in a fluorimeter.

RESULTS OF ANALYSES

Samples of phosphate from Florida and the northwest, of black 

shale, and of carnotite from the Colorado Plateaus were analyzed by 

the direct procedure and also by the extraction fluorimetric procedure 

involving a preliminary extraction of uranium nitrate with an organic 

solvent (part 6). A comparison of the results obtained with the two 

methods is given in tables 1, 2, 3, and 4.

TABLE 1. Fluorimetric uranium analyses of Florida phosphate samples; comparison 

of direct and extraction methods

Sample no.

1.... ............

2... 

3.; . .... _ .........

4...-.. .-......- ....

5.. .......................

6.-.;. __ 

7...... ....... ............

8.... . __

9...... ..... ...........

10 

11. __ ........ ...........

19

13........................

14.. _____ .. .

16. __ ...................

10

in

21........ _ ........

22.......... ..............

BO

24.. ...................

25........................

26 ______ . ..............

27... .. _ - _

28.. 

29 _ - __ ... __ ........

30

11

Percent uranium (determined fluorimetrlcally)

Extraction

0.002 

.001 

.004 

.013 

.006 

.006 

.003 

.002 

.010 

.004 

.005 

.003 

.006

.002 .001 

.001 

.008 

,003 

.005 

.002 

.005 

.004 

.005 

.001 

.003 

.001 

.003 

.008 

.001 

.006

.002

Direct

0.001 

.001 

.004 

.015 

.007 

.005 

.003 

.001 

.006 

.003 

.005 

,002 

.006 

.003

.001

.001 

.009 

.002 

.006 

.001 

.004 

.003 

.005 

.002 

.003 

.001 

.004 

.013 

.002 

.010 

.003

Sample no.

32.. _ ... __ ............

33-. 

34.... .. ,

35.... ............

36.. .... ..................

37.. ......................

38... 

39... ...

40.. 

41.... .

42.... .

43... 

44 __ .... __ ............

45 ______________ .

40

49 ........................

50... 

51.. 

52 ........................

53.. 

54......... ...............

65........................

66... . .

69. .......................

60. 

81......... ...............

62... 

Percent uranium (determined fluorlmetrically)

Extraction

0.000 

.006 

.003 

.001 

.003 

.002 

.003 

.004 

.005 

.002 

.002 

.002 

.008 

.005 

.003 .006 

.011 

.008

.000 

.001 

.005 

.009 

.009 

.001 

.007 

.016 

.018 

.015 

.014 

.012 

.015

Direct

0.000 

.008 

.004 

.003 

.001 

.002 

.003 

.005 

.004 

.005 

.003 

.001 

.008 

.004

.004 .001 

.011 

.010 

.007 

.002 

.005 

.011 

.010 

' .001 

.008 

.015 

.017 

.015 

.015 

.012 

.016
DIRECT FLUORIMETRIC FIELD METHOD FOR URANIUM 73

TABLE 2. Fluorimetric uranium analyses of northwestern phosphate samples; 

comparison of direct and extraction methods

Sample no.

1.. 

2.........................

3....-......... ........

4.........................

6 _ ......................

6......... ..... ...........

7.. .......................

8... 

»....-... .-.. -.._.....

10.. ........... ...........

11.... .....-.-.-......

12.. ......................

13........................

14........................

15....... .. .......... ..

16...... ............ ......

17.. ......................

18.... ...............

19............ .........

20.... ...............

21........................

22........ ................

23

24... 

25....... .................

26......... ... ............

27....... .................

28... .......... ....

29......... ....... ........

30... ................

31....... .................

32........................

Percent uranium (determined fluorimetrlcally)

Extraction

0.001 

.000 

.001 

.021 

.005 

.004 

.001 

.001 

.001 

.004 

.005 

.005 

.001 

.001 

.001 

.001 

.001 

.008 

.004 

.000 

.000 

.001 

.000 

.001 

.002 

.003 

.002 

.000 

.001 

.002 

.001 

.001

Direct

0.001 

.000 

.001 

.018 

.006 

.004 

.000 

.000 

.000 

.004 

.003 

.006 

.000 

.000 

.000 

.000 

.000 

.008 

.006 

.000 

.000 

.000 

.000 

.000 

.002 

.003 

.001 

.000 

.000 

.001 

.002 

.001

Sample no.

33........... .............

34................ .....

35.......... ..............

36... 

37.. ... ...................

38 

39......... ...............

40.... ...... ........

41...... ..................

42........................

43.... ....... ......

44.............. ..........

45.. 

46.. ......................

47.. ..... .................

48.- 

49.............. ..........

60........................

61.. ......................

52....... ..........

53.......... ..............

64..... . ...

55.... . ...... .......

56...... ......

67 

58....... ............

59....... ............

60. 

61... ...............

62........................

63....... .................

Percent uranium (determined fluorimotrically)

Extraction

0.001 

.003 

.001 

.001 

.001 

.005 

.011 

.008 

.011 

.007 

.009 

.007 

.001 

.002 

.003 

.002 

.001 

.002 

.001 

.005 

.002 

.004 

.003 

.004 

.002 

.001 

.002 

.002 

.001 

.013 

.015

Direct

0.001 

.001 

.000 

.000 

.000 

.002 

.009 

.009 

.011 

.004 

.007 

.006 

.001 

.001 

.003 

.001 

.001 

.004 

.002 

.005 

.004 

.005 

.002 

.005 

.003 

.000 

.001 

.002 

.000 

.012 

.016

TABLE 3. Fluorimetric uranium analyses of black shale samples; comparison of 

direct and extraction methods

Sample no.

1.. ....... ................

2..... ..............

3.........................

4.........................

5............... ..........

6........ .................

7...... ................

8... ....... ........

9 _ ......................

10 __ ...... __ ..........

11 __ ....................

12..... . __ ...........

13.... ................

14. __ ..................

15.... ...........

16.... .... .........

17.... ...............

18....... .................

19......... ...............

20-.. 

21....... ...... _ .. _ ...

22

23..... ..............

24....... ........ .........

25.... ...... .......

26.... ...........

27 __ ....... __ .........

28... 

Percent uranium (determined fluorimetrlcally)

Extraction

0.005 

.001 

.006 

.007 

.007 

.004 

.003 

.001 

.001 

.001 

.002 

.003 

.002 

.005 

.004 

.002 

.003 

.004 

.005 

.002 

.001 

.003 

.002 

.003 

.002 

.002 

.001 

.001

Direct

0.005 

.001 

.004 

.006 

.005 

.003 

.001 

.000 

.000 

.000 

.001 

.002 

.002 

.004 

.004 

.003 

.003 

.003 

.004 

.003 

.002 

.003 

.002 

.002 

.001 

.002 

.000 

.002

Sample no.

29....... ............

30....... ..........

31......... ...............

32....... .................

33............ ............

34............ ............

35.......... ..............

36............ ............

37.. ......................

38.....-..... ......

39........ ............

40. 

41 __ ..... _ ....... _ -

42............ ............

43.. .

44........................

45.... ..............

46........ .. ..........

47 __ ....................

48........... ....... ......

49......... ...............

60.......... ..............

61 

62........... .............

53.... 

54....... .................

65... 

56 

Percent uranium (determined fluorimetrlcally)

Extraction

0.002 

.001 

.002 

.001 

.004 

.002 

.003 

.001 

.004 

.002 

.002 

.002 

.002 

.005 

.003 

.001 

.003 

.003 

.005 

.004 

.003 

.001 

.001 

.001 

.001 

.002 

.002 

.001

Direct

0.001 

.001 

.002 

.001 

.002 

.001 

.000 

.002 

.003 

.001 

.002 

.001 

.002 

.006 

.003 

.001 

.003 

.003 

.004 

.004 

.002 

.001 

.001 

.001 

.001 

.001 

.001 

.000

268681 54 6
74 METHODS OF ANALYSIS, URANIUM AND THORIUM10

TABLE 4. Fluorimetric uranium analyses of carnotite samples of 

Plateaus; comparison of direct and extraction methods

Sample no.

I... ................. .

2. ....................

4 . . _ _ . ..

S .... ....

6.........................

7... .

8....... ..................

9.........................

10 __ .............

11.. ... .........

12................. . ...

13..................... .

14........................

15........................

16.................

17................. .

18................. ... .

19.. ....... _______________

20........................

21........................

22.,. ..................

Percent uranium (determined fluorimetrically)

Extraction

0.001 

.001 

.001 

.001 

.001 

.005 

.006 

 .006 

.002 

.004 

.002 

.005 

.013 

.010 

.006 

.001 

.001 

.001 

.001 

.001 

.005 

.003

Direct

0.000 

.000 

.001 

.000 

.000 

.005 

.003 

.004 

.001 

.003 

.001 

.004 

.012 

.008 

.004 

.001 

.000 

.000 

.001 

.001 

.004 

.004

Sample no.

23.- . 

24. 

25. - 

26. -

27 

28. 

29.: ...

30. 

31 

32.. . 

33. 

34

35.............. ..........

36 

37.- 

38 

39 

40. 

41-- -.-.. 

42. 

43. -

Percent uranium (determined fluorimetrically)

Extraction

0.004 

.004 

.006 

.004 

.002 

.014 

.002 

.001 

.002 

.014 

.009 

.002 

.000 

.001 

.000 

.001 

.001 

.001 

.001 

.008 

.002

. Direct

"" O.OOJ1 

 -:003

 -vote

 - .002

 "-.002 

 .015 

 - :002

- :00jj

 ;002 

.000 .ooi

.000 

.000 

.001 

.000 

.000 

.009 

.001

EXPERIMENTS

Materials containing segregated uranium minerals such as carnotite. 

A 1-g portion of each of two samples was ground in a mullite mortar 

and ten 3.0-mg portions of each sample were taken for direct analysis 

to determine whether a sample prepared in this manner would be 

homogeneous. Table 5 gives the results obtained. These results 

indicate that such a procedure yields representative samples.

Effect of sample weight. Uranium was determined in three samples 

by the direct method using for each sample weights of 1.88, 3.75, 7.5, 

and 14.0 mg. The results shown in table 6 indicate that 3.0 mg as a 

sample weight is sufficiently small to minimize quenching of the 

uranium fluorescence.

Fluorescence of other elements in the NaF-Na2C05-K2COz flux. 

Salts or oxides of six elements were weighed, ignited, and fused wiin 

3 g of flux. These discs were read on the fluorimeter, employing excitation of 3600A. The fluorescence intensities measured were 

calculated in .terms of equivalent percent uranium based on a 3.0-mg

sample. .As shown in table 7 none of tne elements in tne amounts

tested gave fluorescence intensities distinguishable from a blank.
DIRECT FLUORIMETRIC FIELD METHOD FOR URANIUM 75

TABLE 5.- Determination of uranium, in percent, to show homogeneity of two 

samples containing segregated uranium minerals

[Samples from the Colorado Plateaus]

Sample no. 1

0.017 

.018 

.019 

.020 

.019

Sample no. 2

0.015 

.< . 014 

.012 

.014 

.016

Sample no. 1

0.020 

.019 

.019 

.019 

.023

Sample no. 2

0.013 

.014 

.013 

.015 

.013

TABLE 6. Effect of sample weight in the direct method

Sample

Shale... . . . .

Florida phosphate. ________________ . _____

Weight (mg)

f 1.88 

1 3.75 

1 7.50 

I 14. 00 

I 1.88 

1 3.75 

1 7.50 

I 14.00 

1.88 

3.75 

7.50 

14.00

Percent uranium

Extraction

0.007 

.010 

.009

Direct

0.005 

.006 

.004 

.004 

.011 

.009 

.008 

.007 

.008 

.008 

.007 

.006

TABLE 7. Equivalent fluorescence of elements other than uranium

Material

NbsOi....... .

(NHOjCe(NOi)j-4HsO--.

Weight of 

oxide (mg)

6.7

15.0

15.0

5.4

Equivalent 

uranium 

(percent)

0.000

.000

.000

.000

Material

Nd(NOj)s-6HjO .. .....

Y(NO»),.6HjO- ......

Blank....................

Weight of 

oxide (mg)

12.0

8.8

0

Equivalent 

uranium 

(percent)

0.000

.000

.000

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 10. AN IMPROVED FLUORIMETER FOR THE DETERMINATION OF URANIUM IN FLUORIDE MELTS

By MARY H. FLETCHER and IRVING MAY

CONTENTS

Page 

Introduction. .. _ ._____________.__._._ 77

Description of the instrument.___.__________________________________ 79

Performance of the instrument._____________________________________ 80

ILLUSTRATIONS

PLATE 3. Rear-view assembly and expanded details of the modified

fluorimeter______________________________________ In pocket

FIGURE 9. Complete assembly of the modified fluorimeter_____-_-____ 79

10. Standardization curves for 3.0-g discs prepared by fusion in

30-ml crucibles.._____________________ 80

11. Standardization curves for 1.5-g discs prepared by fusion in

crucible lids... _____ _._ ., 81

12. Calibration curve for routine work__________________._____ 83

INTRODUCTION

The Model R fluorimeter has been modified to increase its stability 

and sensitivity. The new instrument is about 10 times as sensitive 

as the original fluorimeter, but it can also be employed conveniently 

at a sensitivity level comparable to or less than that of the Model R 

fluorimeter.

The Oak Ridge Model R fluorimeter (Coleman, C. F., C-4.381.4, 

1946) was in constant use at the Geological Survey for 6 months and 

proved to be very useful. When it became apparent that a more 

sensitive and stable instrument would better meet the particular 

needs of this laboratory, an improved fluorimeter for use in the 

analysis of low-grade samples was constructed. The new instrument 

has the folio whig advantages over the Model R fluorimeter:

1. Greater sensitivity.

2. Increased electrical stability.

3. Greater flexibility, by which a wider range of fluorescence can 

be measured.

NOTE. This report was Issued as Trace Elements Inv. Kept, J20,1950.

77
78 METHODS OF ANALYSIS, URANIUM AND THORIUM

In the Model R fluorimeter, the ultraviolet lamp is fastened directly to the instrument and there is no provision for cooling, although it is characteristic of high-pressure mercury lamps that their 

intensity is, among other things, a function of their ambient temperature. As a result, when the instrument is used for 30 to 40 minutes 

after a 10-minute warmup period, there is a decrease of about 30 

percent in the instrumental sensitivity because of increased lamp 

temperature. It is, therefore, frequently necessary to turn the lamp 

off, allow it to cool, and restart it to maintain a usable range of sensitivity. This is not only a time-consuming process, but it is a poor 

practice inasmuch as such lamps undergo the greatest wear during 

the starting period. Furthermore, the high operating temperature 

of the unventilated lamp, as it is used in the Model R instrument, 

raises the temperature of the phototube and causes a constant drift 

of the zero of about four or five divisions after each reading. Such 

a change introduces some uncertainty in the readings. It also necessitates resetting the zero point after each reading.

In the first model of the new fluorimeter, the minimum changes 

consistent with our requirements were made, and several parts of the 

Model R instrument were incorporated in the modified fluorimeter. 

The substitution of the more intense General Electric E-H4 or C-H4 

lamp in the new .instrument increases its sensitivity yet allows the 

continued use of the Photovolt Electronic Photometer (Model 512). 

A constant wattage transformer designed for use with H4 lamps is 

required. The lamp is supported on a stand and is ventilated by a 

ventilating fan (obtainable at photographic stores). After a 30- 

minute initial warmup the operating temperature remains constant, 

and the lamp can be left on all day if desired; furthermore, the phototube remains cool, and most of the drift is eliminated.

A feature of the new fluorimeter is a convenient sensitivity COntrOl

beyond the 25-percent change in sensitivity possible with the photometer unit. As the lamp is not mounted directly on the instrument, 

the distance between the lamp and sample may be changed readily. 

Extra sensitivity control results from the variation in intensity of 

illumination according to the inverse square law as the distance between the sample and lamp is changed. For instance, with the E-H4 

lamp 12 inches above the sample (s% irxekes above the primary filter)

and the pnOtOttieter Unit Set fOr lOWest sensitivity, the standard glass

supplied with the Model R fluorimeter will give a reading of 1000.

TKIS is about twice the usable SeHSitlVlty Of the Model R fluorimeter. 

WnemteJtilfi tWpea to ^tK1~ 6 Relies of the sample (3 inches 

from the primary filter), the sensitivity IS increased tO elgnt times v~ 

sensitivity of the Model R instrument. For still greater sensitivity 

a C-H4 lamp is usedn3aboufl%"inches above the primary filter; thi§
IMPROVED FLUORIMETER FOR DETERMINATION OF URANIUM j

arrangement gives a sensitivity about 10 times that ©fStflie Model

CRIPTION OF THE INSTRUMENT

flat black

instrument is built on the 

to<a^e:fa!ins.the sample slide, t 

ers of the old in 

made from 2 

.. A no. 6 ' Pack¥rd f 

a iK-i

fil't'ersto ^

hole in the center^^ _0ne jnd of a brass collar is held in this hole^y a 

ffiction fit, and [the other end is threaded to £ crew directly into the 

search u: lit: Air-joints -aTe"^ecure~and~lrg:frt~i ;iglitT~~The secondary

Tlllf"HT*Q O T*; V ifiO \r&\lC\T\r QTHi O*T*OOT1 Tl I rO^Q fl V\"PT^Tnnr nrtC Qa_Cft d T\ Ji\ Q7Q^ IJilUtJIJstllj j\ t»ilt3 VtJlJlUW ctLLU. f^\Y^r^ -MM ^ ^-mVv^- ".''JHj r JlAU^t grOptoO-_<i'J.l(it^rt7>/ oU.

molded lljuckne^fBQJiriict&Qg!^^ =AJCornin» filter 

Jo\874, L3-}ti filter. A

*^vM!*_viwv*^..^.*.v-^«>«*_«^«a_airjKen^ ie-instr4^jent, 

aid the (Jnclosure is ventilated with a ventilating fan.

GOT

sheet-

.ayldiaiiTJ ta-0£ ui aolsul y;d bneqDiq eoslb g-Q.S lol aaviuo uoWssibisBflfija .01
80 METHODS OF ANALYSIS, URANIUM AND THORIUM

PERFORMANCE OF THE INSTRUMENT

The instrument equipped with an E-H4 lamp was first tested with 

the glass standard provided with the Model R fluorimeter. After a 

10-minute warmup period the distance of the lamp was adjusted to 

give a reading of 1000. After 20 minutes the reading had dropped to 

900. Readings of 900 were then obtained at intervals over a period 

of 5 hours. The initial drop from 1000 to 900 indicates the need for 

at least a 30-minute warmup period to obtain equilibrium.

The performance of the instrument was then tested with standard 

samples. These were of two kinds: first, a series of 12 standards 

containing from 0 to 3 micrograms of uranium prepared by fusion in

1000

900

800

700

Z 600 

o

500

400

300

A= Light 8 t"obove primary filter; gloss $tandard=IOOO

B Light 3"above primary filter

C= Model R - Fluorimeter j glass standard = 600

.1 .2 .3 .4 .5 .6 .7

MICROGRAMS OF URANIUM 

FIOUBE 10. Standardization curves for 3.0-g discs prepared by fusion in 30-ml crucibles.
IMPROVED FLUORIMETER FOR DETERMINATION OF URANIUM 81

30-ml platinum crucibles with 3 grams of fusion mixture; 1 second, a 

series of 8 standards containing from 0 to 0.15 microgratn of uranium 

prepared by fusion in platinum lids with 1.5 grams of the same flux. 

Each of these two sets of standards was read in the instrument with 

the lamp 8% and 3 inches above the primary filter. As many as 10 

to 20 discs could be read without resetting the dark current. The 

curves obtained in these experiments as well as a comparison curve 

obtained with the Model R fluorimeter are given in figures 10 and 11. 

soo

400

A- Light 8£"above primary filter; gfass standard = 1000 

B= o- Lightnr 3" o aboveo primary primary filter mi

C = Model R - Fluorimeter jglass standard * 600

0 .05 .10

MICROGRAMS OF URANIUM 

FIGURE 11. Standardization curves for 1.5-g discs prepared by fusion In crucible lids.

i 9 percent NaF In NaiCOi, KjOOj (1+1 by weight). The pellets were removed from the crucibles be 

fore the measurements were made.
82 METHODS OF ANALYSIS, URANIUM AND THORIUM

The modified fluorimeter has now been in constant use for almost 

2 years and has proved to be very satisfactory. However, future 

models 2 may incorporate such changes as a different lamp support to 

give better and easier lamp adjustment, a built-in slide for cutting the 

intensity of the exciting light, and possibly a different base and 

sample holder. The photometers can be purchased with additional 

2X and 5X ranges added to the original "Hi" and "Lo" scales. These 

new ranges increase the precision for those readings just beyond the 

range of the Hi scale.

Many of the samples analyzed in this laboratory contain less than 

0.02 percent of uranium, and few contain more than 0.04 percent. 

These determinations are usually made by the method described by 

Grimaldi and Levine (part 6). An aliquot which contains 3.75 mg 

of sample is Used for the preparation of the phosphors. One of the 

instruments has been adapted specifically for the convenient handling of these samples.

For this purpose a C-H4 lamp 1^ inches above the primary filter is 

the source of exciting light, ?and only 'the 'Lo scale of', the* photometer 

is used. Standard curves are drawn to give direct readings in percent of uranium (fig. 12). Curve A (0 to 0.019 percent uranium) 

was obtained when the glass standard (a Corning polished glass 

filter, no. 3384, melt 600,3 2 niches square, masked down to a 0.8-inchdiameter circle) read 80 divisions; in this curve one scale division is 

equivalent to 0.00022 percent uranium. For curve B (0 to 0.066

percent uranium) the intensity of the exciting light was cut down by

interposing 2 nichrome gauze squares keWeen ike lamp and the 

instrument. With this arrangement the glass standard read 25 

divisions, and one scale division was equivalent to 0.00068 percent 

uranium. Once the curves are prepared, it is necessary only to set 

the instrument to give the proper reading with the glass standard. 

Occasional checks; of the curve are made with uranium standards, 

particularly when a new batch of flux is used

' New models have been constructed but when this Bulletin was sent to the printer descriptions and shop

arawinBa 0* them were not yet available.

 Different melts of filters bearing tUG same number vary greatly in fluorescence. NO. 3384 UllCIS PUT1 

cbased in recent years have shown very little fluorescence and Cannot be used as glass standards.
CURVE B, PERCENT URANIUM IN A 3.75-mg ALIQUOT 

0 .01 .02 .03 .04 .05 .06 .07

IUU

90 

80

70

5

Z 

O

UJ 

_l 60 

< 

O

S3

=_ 50

Z 

O

0 

UJ

_l £ 3o

20 

10'

i 

o

/

A>

-

A = Regular arrangement 

8=2 wire-gauze squares between 

light ond primary filter.

A

7

A

/,

/

/

/

/

/

>

V

/

(

/

i j

/

/

/

V

/

/

/

B/

/

A

/

A/

/

/

/

f

/

/

'

0 .005 .01 ..015 

CURVE A, PERCENT URANIUM IN A 3.75 -mg ALIQUOT

FIGURE 12. Calibration curve for routine work.

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 11. A TRANSMISSION FLUORIMETER FOR USE IN THE 

FLUORIMETRIC METHOD OF ANALYSIS FOR URANIUM

By MARY H. FLETCHER, IRVING MAY, and MORRIS SLAVIN

CONTENTS

Abstract__ _____________________________________________________ 85

Introduction._____________________________________________________ 86

Advantages of a transmission fluorimeter.__--__-_-___-_-____-________ 88

Sensitivity _ ______________________________________________________ 88

Description of the instrument.______________________________________ 89

Preparation of melts--_-----_-_-_______..-____-______-_____________. 90

Performance of the instrument._____________________________________ 91

ILLUSTRATIONS

FIGURE 13. Schematic diagram of a "reflection"-type fluorimeter____.___ 86 

14. Schematic diagram of a transmission-type fluorimeter-______ 87

TABLES

TABLE 1. Effect of melt thickness on instrument response._____________ 90

2. Performance of the "pick-up" units_-_-__-__-_______________ 91

3. Readings of replicate blank samples_______________________ 92

4. Readings of replicate standard samples______________________ 92

5. Replicate analyses of standard sample GST-1 ____.___--_--_-_ 92

ABSTRACT

A fluorimeter has been built which measures fluorescence by transmission rather 

than by the usual "reflection" methods. The consequence of the adoption of 

this new principle is a large gain in simplicity, compactness, ruggedness, sensitivity, 

cheapness of constructor, and efficient use of light energy.

When used with an uncooled 1P21 photomultiplier tube operated at 50 volts 

per stage and a d-c amplifier, the instrument has a sensitivity of one scale division 

equivalent to 1.7X1Q-10 g of uranium in 1.5 g of flux. However, in practice the 

lower limit is set by the blank reading. As a consequence of compactness and 

compartmentalization, stray light, which contributes to this blank reading, is 

reduced to a very small amount.

Reproducibility is such that a few thousandths of 1 percent of uranium can 

be determined on a 0.05-mg sample with an error of about 5 percent of the amount 

present.

Efficiency of light use is so great that commercial photometers using simple 

phototubes may be substituted for the photomultiplier tube and d-c amplifier.

NOTE. This report was[issued as"Trace Elements Inv. Kept. 104,1949. "
86 METHODS OF ANALYSIS, URANIUM AND THORIUM

INTKODTJCTION

Fluorescence of solids of the type exemplified by the alkali carbonate-fluoride melts used in the fluorimetric determination of uranium 

is generally measured by irradiating the surface of the melt with 

ultraviolet light and picking up the fluorescent light from the same 

surface by means of a phototube. A typical arrangement is shown 

schematically in figure 13. The Argonne fluorimeter, J 2 the Oak Ridge 

Model R fluorimeter,3 and others are based on this principle.

In the transmission fluorimeter, by way of contrast, the lamp and 

phototube are on opposite sides of the melt. Figure 14, is a schematic 

drawing of this arrangement. Transmission measurements were probably overlooked by earlier workers because they considered their 

melts opaque, because of mechanical difficulties in the removal of the 

inelts from the containers in which they had been fused, or simply

raumsii; 'io da9s>7yq ? lc 3iilhnu-v..'o:tl -.7

eili lo i t8&ffl?^t?gf^ boninwateb sd

> Price, G. E., FerrettI, R. J., and Schwartz, 8., 1948, ANL-4113. 

Ooleman, O. F., 0-4.381,1946;8- 01 ^Oi
TRANSMISSION FLUORIMETEB 87

because the other system worked satisfactorily. Transmission methods are entirely feasible because tests have shown that the melts are 

translucent, not opaque and that proper choice of a fusion mixture 

gives a melt which is easily removable from its container and strong 

enough to be handled.

Primary filter

Sample

Secondary

filter

Shutter

Phototube

FIQUBB 14. Schematic diagram of a transmission-type fluorimeter.
88 METHODS OF ANALYSIS, URANIUM AND THORIUM

ADVANTAGES OF A TRANSMISSION FLUORIMETER

Compactness and simplicity are the first and obvious advantages 

of an instrument based on the transmission principle. The linear 

arrangement of parts, with the ultraviolet source and phototube on opposite sides of the sample, makes it possible to bring both the ultraviolet light and the phototube very close to the sample. Thus 

maximum use is made of the exciting light, and a relatively large part of 

the transmitted fluorescence reaches the phototube. This is an efficient arrangement that greatly reduces losses in light intensity due 

to the inverse square law.

When a sample is in position in the transmission fluorimeter J 95 to 

98 percent of the initial ultraviolet light is reflected upward from the 

surface of the sample. Of the remaining 2 to 5 percent, about eighttenths is absorbed; consequently, not more than 0.5 to 2 percent of 

the original exciting radiation can pass to the lower part of the instrument where it might cause stray fluorescence. This results in a 

low instrument blank. In contrast to this, the entire inner surface of 

a simple reflection fluorimeter (one without an optical system) is irradiated by the full intensity of the exciting light, and the inner surface is very large in comparison to that of the transmission fluorimeter. In a reflection fluorimeter, the reading obtained for a blank 

melt corresponds to the fluorescence of the melt plus about an equal 

or greater response from the instrument itself. But in a transmission 

fluorimeter the reading obtained for a blank melt is due almost wholly 

to the melt alone.

Simplicity of the instrument results in ruggedness and cheapness of 

construction. There are no lenses or mirrors and no need for 

delicately adjusted parts.

SENSITIVITY

The sensitivity of the Argonne and Oak Kidge fluorimeters, as well 

as the one described here, is such that all give a measurable blank 

reading. Consequently it is meaningless to express limiting sensitivity in such terms as galvanometer deflection per unit weight of 

UTaniuni, for it is the blank which limits further improvement, not 

inefficiency of exciting light nor insensitivity of phototube. Tn6

main factors contributing to the blank are impure flux, fluorescent or

lefl/ky filters, and stray light in the instrument. The first is a chemical problem in purification of reagents; the second is a problem for

the filter makers; only the third is amenable to reduction by good 

desigll Of inStrUment, The transmission fluorimeter, therefore, with

its compact linear arrangement of parts and consequent Very lOW 

stray light, is inherently very sensitive.
TRANSMISSION FLUORIMETER 89 

DESCRIPTION OF THE INSTRUMENT

The Model II transmission fluorimeter described in this paper was 

designed to give maximum flexibility for research purposes and is intended as an intermediate model. More specifically, all filters are 

readily removable and exchangeable, the exciting light is on a sepate stand so that lamps may be interchanged, and the "pick-up" 

units of different measuring devices are in separate and identical 

housings that are threaded to screw into the bottom of the fluorimeter proper. Future models will not require this amount of flexibility and will undoubtedly be more compact; also, there are obvious 

changes that will be necessary. For example, the Model II as built 

was not as light tight as later proved to be necessary so that masking 

tape had to be used around the joints and extra light traps were 

added to prevent light leakage around the front and back shutter 

rods.

The basic design of the instrument resembles a miniature chest of 

drawers. The housing is made of brass and the drawers of maple 

and brass. The uppermost drawer carries the primary or ultraviolet 

filters; the middle drawer contains a disc of nonfluorescing glass over 

the bottom aperture and is equipped with an adaptor to hold the 

sample; the lower drawer holds the secondary filters.

The filter combination finally adopted for general use consists of 

two Corning No. 5874 2-inch polished squares as the primary filters, 

and a 2-inch square interference filter peaked at 5550A for the secondary. The exciting light is furnished either by a General Electric 

C-H4 or E-H4 lamp. Lamp voltages are regulated by a constant 

wattage transformer specifically designed for use with the H 4 lamps. 

Temperature of the lamps is controlled by ventilation with a darkroom ventilating fan.

The measuring devices are either a photometer equipped with a 

simple phototube, or a 1P21 photomultiplier tube in combination 

with a d-c amplifier. Voltage for the 1P21 photomultiplier tube is 

supplied by a regulated power supply with voltage divider of conventional design. The d-c amplifier design is slightly modified from 

that used by Schulman, Battey, and Jelatis,4 with their polarograph 

and is based on the fundamental design of Koberts.5

The modification consists hi deletion of the circuit for applied 

voltage, reversal of polarity, and appropriate changes in the sensitivity 

ranges.

* Schulman, J. H., Battey, Bruce H., and Jelatis, D. G., 1947, A new polarograph: Rev. Sci. Instruments, 

v. 18, p. 226-231.

 Roberts, Shepard, 1939, A feedback micromicroammeter: Rev. Scl. Instruments, v. 10, p. 181-183.

268681 54 7
90 METHODS OF ANALYSIS, URANIUM AND THORIUM

PREPARATION OF MELTS

The fusion mixture used for the preparation of the melts is that 

described by Grimaldi and Levine (part 6) and consists of 9 percent 

sodium fluoride hi equal parts by weight of sodium carbonate and 

potassium carbonate. This mixture melts at a little below 650 C 

and shrinks slightly on cooling so that the melt pulls away from its 

container. The melts are strong and can be handled without danger of 

breaking. The fusion mixture is prepared by fusing several 100-g 

portions which are then ground and mixed. This procedure was 

necessary to obtain a uniform mixture that would give reproducible 

blanks. Melts were prepared by fusion of 1.5 g of this mixture in 

platinum lids from 30-ml crucibles. The fusions were made hi a 

furnace at 650 C.

Although, as might have been expected, fluorescence varies inversely 

with thickness of the melt, these variations of thickness present no 

practical difficulties. Standard size lids are chosen for the fusions, 

hence, the weight of the flux controls the thickness. Differences in 

weight as large as 5 mg introduce an error in the fluorescence reading 

of only 0.2 percent. Variations in thickness with weight and the 

corresponding changes in the instrument response are given in table 1. 

It should be stressed that even relatively thick melts are translucent. 

Also the greatest sensitivity occurs with the thinnest melts. This 

could be predicted from mathematical considerations.

TABLE 1. Effect of melt thickness on instrument response 

[Measurements made with the 1P21 photomultiplier tube and d-c amplifier]

'Weight of flux (grams)

0.5... 

1.0. . 

1.5 

2.0.... . . .. .................

2.6..... 

3.0.. . 

Thickness of 

melt (inches)

0.017 

.027 

.040 

.049

.058

.070

Scale divisions (0.02

scale)

Blank reading

21.8 

20.8 

20.4 

22.5

20.6

18.6

0.003 microgram of 

uranium

43.5 

40.4 

38.0 

36.5 

33.6 

29.8

Sensitivity 

(microgram of uranium 

per scale 

division)

0.000138 

.000153 

.000171 

. 000214 

. 000231 

.000268

It; 16 difficult to cover the lids evenly with 0.5 to i.o g of flux, and

for this reason 1.5 g was the most convenient to use. The larger 

amount Of flUX Will alSO allOW for the presence of larger amounts of

quenclier elements, as Pi-ice a Ko,s sKowra. -fclxa,t, -fcKo ratio weiglit of

quencher to weight of flux is the important factor in quenching

phenomena.

1 Price, George B,., Ferretti, R. J., and Schwartz, Samuel, 1945, The microfluorometric determination of 

uranium: AECD-2282.
TRANSMISSION FLUORIMETER 91

PERFORMANCE OF THE INSTRUMENT

A standard curve is obtained by measuring a series of melts which 

contain known amounts of uranium. At the same time a reading is 

made with no sample in place. This reading is called the "standard 

deflection" and represents filter leakage or fluorescence and is a constant of the instrument. Once a standard curve has been drawn, 

the conditions under which it was made can be reproduced by adjusting the voltage applied to the phototube, or the distance of the 

lamp to give this standard deflection. The uranium content of 

unknown is obtained by interpolation in the standard curve.

The performance of the instrument with two different pick-up 

units, the photomultiplier tube with the d-c amplifier and the 

Photo volt photometer (no. 512) with a "C" search unit, is shown in 

table 2. It will be seen from the table that the two may be used for 

the same amounts of uranium. However, the Photovolt photometer 

is operated at capacity but the more elaborate system of a 1P21 

photomultiplier tube and d-c amplifier still has a large reserve oi 

unused sensitivity. For instance, if the voltage per stage were 

increased from 50 to 100 the amplification would be increased about 

one hundredfold.7

TABLE 2. Performance of the "pick-up" units

Lamp type

O-H4..... ... ..... ...

E-H4........... ..

Lamp distance 

(inches)

1

3

"Pick-up" unit

1P21 d-c amplifier....... _ ...

Volts 

per 

stage

45

Blank 

reading 

(scale 

div.)

»22.0

>20.0

Sensitivity 

(microgram 

equivalent 

to one div.)

10.00015

1 . 000171

1 1 scale. 

> 0.02 scale.

The sensitivity of the instrument with either pick-up unit is 

roughly equivalent to that of the Argonne instrument, although the 

available data are insufficient to make an exact comparison. However, Price 8 operated his photomultiplier tube at 80 volts per stage 

(compared to 50 volts in this instrument) and used dry-ice cooling 

for the phototube.

Results obtained with the transmission fluorimeter are shown in 

tables 3, 4, and 5. The E-H4 lamp was used at a distance of 3 inches 

from the primary filter, and volts per stage on the 1P21 tube were 

50. The scale setting with no melt in the holder was 46.0 divisions 

on the 0.02 scale.

7 Engstrom, Ealph W., 1947, Multiplier phototube characteristics; application to low light levels: Jour. 

Optical Soc. Am., vol. 37, p. 421. 

« Price, Q. R., Ferretti, R. J., and Schwartz, S., 1948, ANL-4113.
92 METHODS OF ANALYSIS, URANIUM AND THORIUM

The data in these tables show that performance of the instrument 

is adequate for analytical purposes. The errors are no greater than 

those inherent in the chemical manipulations of sampling, weighing, 

and pipetting that precede the photometry of the fluorescence.

TABLE 3. Readings of replicate blank samples

 Sample no.

1 .... . ...-

2....... ... ... 

3 . 

4... 5.. ~ 

6.- 

Scale 

divisions 

(0.02 scale)

21.0

22.0

21.0

21.5

20.1

20.2

Deviation 

from mean

0.2

1.2

.2

.7

.7

.6

Sample no.

7__. ~

8........ .......... .......

9. _ .....................

10...-. .......... ......

Scale 

divisions 

(0.02 scale)

20.0

-20.2

21.1

20.9

20.8

Deviation 

from mean

0.8

.6

.3

.1

.54

TABLE 4. Readings of replicate standard samples 

[Uranium content=0.005 microgram]

Sample no.

1 _ . _ ....... _....___. 

2 __ .... __ .-..._ ....-

3...... ... ... .... ... ...

4..-..... .... ... ....

5..... ................ ....

6.. ........ ......... ...

7. ... ... ... ...

Scale 

divisions 

(0.05 scale)

20.5

19.9

20.9 9ft s

20.8

20.7

21.0

Deviation 

from mean

0.3

.9

.1

.0

.0

.1

.2

Sample no.

8 ....- .............

9... ...................... 10..-....-....-.........:.

Blank.... ................

Scale 

divisions 

(0.05 scale)

21.2

21.0

91 n

20.8

8.1

Deviation 

from mean

0.4

».24

1 0.24 scale divisions on 0.05 scale is equivalent to 0.6 scale divisions on 0.02 scale. The ratio of the 0 02 scale to the 0.05 scale is 1:2.5.

TABLE 5. Replicate analyses of standard sample GST-1 (Uranium content=0.009

percent)

[100-microgram aliquots of sample]

Replicate no.

1............ .............

0

o

4 __________

5 - __________

6... ..... ... ... ..... 

7. ...................

Uranium (micrograms and

percent)

0. 0085

.0085

flflfiS

.0088

.0088

.0091

Deviation 

from mean

0.0002

.0002

.0001

.0001

.0001

.0004

Replicate no.

8.-. .................

9... .. 

10...... 11........ ................

Mean. ____ ....

Uranium (micrograms and 

percent)

0. 0086

.0081

.0086

.0088 

.0088

Deviation

from mean

0. 0001

.0006

.0001

.0001

.0001
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 12. THE DESIGN OF THE MODEL V TRANSMISSION

FLUORIMETER

By MAEY H. FLETCHER, IRVING MAY, and JOSEPH W. ANDERSON

CONTENTS

. Fase

Abstract..__._..___________._____.___.__...___ 93 

Introduction._____________________________________________________ 93

Acknowledgments -_----_-_-___-_-_______________._____-_-_-_------ 95

ILLUSTKATIONS

[In pocket] 

PLATE 4. Fluorimeter assembly

5. Cutaway view, cross section, and details of parts of "fluorimeter"

6. Details of parts of fluorimeter assembly shown in plate 4

7. Details for construction of shield

8. Details for construction of type--? phototube housing

ABSTRACT

A transmission fluorimeter for the measurement of the fluorescence of uranium 

in fluoride melts is described. The instrument incorporates several improved 

features that have not been published previously. Unlike the earliest models, 

the design of the new fluorimeter, with its close machining of parts, reduces the 

possibility of light leakage and also increases considerably the ease with which 

the various components of the instrument may be assembled and adjusted. The 

Model V fluorimeter is a very rugged instrument with a compact arrangement of 

parts. It possesses great flexibility so that various phototubes, measuring 

devices, light sources, and filter combinations may be used interchangeably.

Detailed shop drawings are given for the construction of the fluorimeter.

INTRODUCTION

The use of transmission fluorimeters for the measurement of the 

fluorescence of uranium in fluoride melts has been discussed in other 

papers (parts 8, 11, 13). *

The Model II fluorimeter was described (parts 8 and 11) without 

detailed drawings inasmuch as it was an experimental model.

NOTE. This report was Issued as Trace Elements Inv. Kept. 133,1950.

 May, Irvlng, and Fletcher, Mary H., 1948, A preliminary report on a transmission fluorimeter: U. 8. 

Geol. Survey (unpublished report)

93
94 METHODS OF ANALYSIS, URANIUM AND THORIUM

Newer models have been built, and the Model V instrument 

described in this paper incorporates the various unproved features 

of these instruments. No further marked changes in design are 

contemplated, and therefore we are presenting detailed drawings of 

the instrument.

Like earlier models, the Model V was designed to be a sturdy, 

light-tight instrument, having compact arrangement of parts and 

great flexibility. Various phototubes, measuring devices, light 

sources, and filter combinations may be used interchangeably. The 

chief difference between the two fluorimeters is that the Model II is 

rectangular whereas the Model V is cylindrical.

For clarity the word "fluorimeter," in quotation marks, as used in 

this paper refers to that part of the complete fluorimeter that houses 

the filters, sample slide, and shutter.

The Model V "fluorimeter" is machined from solid brass. The 

"fluorimeter" head includes the sample slide, shutter, and a holder 

for the primary filters. The sample slide is provided with adaptors 

so that several sizes of fluoride melts may be accommodated. The 

secondary filters are in the bottom plate which screws into the "fluorimeter" head. The bottom plates are of two types A and B. Type 

A is used with an RCA 1P21 photomultiplier tube or with the Photovolt Electronic Photometer (Model 512). It is threaded to fit the 

Photo volt search unit. Housings for the 1P21 photomultiplier tubes 

have the same thread as the search unit so that either phototube can 

be used with the type-A plate. The tjpe-A plate is constructed so 

that phototube housings can be removed or installed while the "fluorimeter" is in position on the supporting stand. The type-# bottom

plate is used with the RCA 5819 photomultiplier tube. The Cinch 

no. 3M14 socket with mounting ring 3R14 is used with this tube. 

The filter holders are made for 2-inch-square filters. An adaptor

ring for each filter holder permits the use of filters of different

thicknesses.

The instrument is shown in detail in plates 4 8. In plate 4 onehalf of drawing A is a section showing the fluorimeter assembly with 

type-A bottom plate and search unit in place; in plate 4 drawing B

shows the arrangement with type-5 bottom plate and 5819 photomultiplier tube. The stand, lamp support, and shield are the same 

for both arrangements. Plate 5 is a cutaway drawing showing additional details of the "fluorimeter." The remaining plates are detailed 

shop drawings for the construction of parts shown in plates 4 5. All

parts of the "fluorimeter'' shown in plate 5 must be machined to a

class-4 fit or better; those shown in plate 5 require only a class-3 fit,

A thin glass disc (not shown in the illustrations) is required in the

sample slide under the adaptor ring. The purpose of this disc is to
DESIGN OF MODEL V TRANSMISSION FLUORIMETER 95

prevent flakes of the sample from falling into the fluorimeter. This 

glass must be nonfluorescent. Discs cut from photographic plates 

used in spectrum analysis are satisfactory.

The lamp shown in plate 4 is a General Electric E-H4 or C-H4 

lamp. This lamp requires a porcelain socket with an "admedium" 

base. It is operated with a constant wattage transformer designed 

especially for H-4 lamps. The lamp temperature is controlled by 

ventilation with a darkroom ventilator.

The primary filters are 2-inch-square Corning no. 5874 ultraviolet 

filters, polished thickness. Two of these filters are generally used. 

The secondary filters may be either a combination of Corning filters 

nos. 3486 and 9780, molded or polished thickness, or an interference 

filter peaked for maximum transmission at 5550A.

Various combinations of phototubes, and current amplifying and 

measuring devices that may be used with this "fluorimeter" have 

been described elsewhere (part 11 and 13).

ACKNOWLEDGMENTS

We gratefully acknowledge the contributions to this project by our 

associates at the Geological Survey.

We are especially indebted to Alexander E. Herold, Jr., who did 

all of the machine work and made many valuable contributions to 

the final design.

Special thanks are also due to Joseph Ramisch who assisted in the 

original design.

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 13. A BATTERY-POWERED FLUORIMETER FOR THE 

DETERMINATION OF URANIUM

By IRVING MAY and MARY H. FLETCHER

CONTENTS

Page 

Introduction______________________________________ 97

Acknowledgment __________________________________________________ 98

Description of the instrument-______________________________________ 98

Performance of the instrument___-_--_-___.____.-_________-____-.___ 102

ILLUSTRATIONS

FIGURE 15. Lamp circuit used in the instrument-_____________________ 99

16. Reflecting support for the lamp_________________________ 101

17. Power circuit for the photomultiplier tube _________________ 101

18. Standard curve______________.-___--__-_-_________ 102

19. Platinum dish used for fusion._______-_-_______--_--___-_ 103

INTKODUCTION

This report describes a transmission fluorimeter that is completely 

battery-powered and suitable for use in the laboratory, in field stations, or in mobile units. The source of the ultraviolet light is a 

3-watt RP-12 lamp. The instrument is sufficiently sensitive for 

the determination of 0.001 percent uranium in a 0.4-mg sample.

The determination of uranium by measuring the fluorescence of 

fluoride melts has been used extensively in the past few years as a 

laboratory procedure. With an appropriate fluorimeter this technique could be developed into a field method for the determination of 

uranium.

A fluorimeter for field use, either in a mobile laboratory or at a 

field station, would have to be completely battery-powered. Although there are a number of fluorimeters in general Use that employ 

battery-powered current-amplifying and measuring devices, they all 

require house current as a source of power for the ultraviolet light. 

The fundamental problem in designing a field fluorimeter therefore 

resolves itself into finding a suitable ultraviolet lamp that can be 

operated with batteries.

NOTE. This report was issued as Trace Elements Inv. Kept. 136,1060.

97
98

The instrument described in this paper uses an inexpensive 3-watt 

d-c lamp as the source of ultraviolet light. The arrangement of the 

sample support, filters, and shutter is the same as the one used in the 

transmission fluorimeter described in a previous paper (part 12). 

The fluorescent light is converted to electrical energy by a batterypowered photomultiplier tube, and the resulting current is read 

directly with a sensitive but sturdy microammeter.

ACKNOWLEDGMENT

We thank Dr. Francis J. Davis, Division of Health Physics, Oak 

Ridge National Laboratory, for his recommendations about phototubes and meters, and for assembling a prototype current-measuring 

unit.

DESCRIPTION OF THE INSTRUMENT

The ultraviolet lamp. The source of the ultraviolet light is a small 

d-c RP-12 lamp, manufactured by the General Electric Co. for 

lighting fluorescent instrument dials on aircraft. The lamp is coated 

on the inner surface with a phosphor having a radiation peak at 3500A. 

The RP-12 lamps are available in two wattage ratings, 3 watts, 12-16 

volts, and 4 watts, 24-28 volts. The lamp has a length of 2% inches, 

a maximum diameter of 1% inches, and a regular double-contact 

bayonet base with indexed pins. The lamp circuit used in this 

fluorimeter is shown in figure 15.

Despite its lower light output, the 3-watt lamp has been adopted 

for this instrument because of the greater convenience in working 

with lower voltage batteries. The light produced by the 3-watt 

lamp is much less intense than that from 100-watt lamps or larger that 

normally are employed in fluorimeters. Therefore the 3-watt lamp 

might seem unsuitable for use in a very sensitive fluorimeter. The

Overall Sensitivity Of the transmission fluorimeter (parts 11 and 12) 

is so great, however, that for normal use in uranium analyses the lamp 

is raised about 10 inches from the primary filter and the photomultiplier tube is operated at only 450 volts rather than at its maximum voltage. In the field fluorimeter, however, the low light 

output of the 3-watt lamp is compensated for largely by placing the

lamp nearly in contact with the primary filter and operating the

photomultiplie'r tube at 900 volts.

The lamp generates very little heat; even when it is close to the

filter and cohered waft a reflecting dome, Mb is no necessity for

cooling with a fan. The light output of the lamp becomes reasonably Stable less than 5 minutes after lighting. i>ower s priy for tfa famp Twv types of toattenes Have Deen

investigated to supply current for the lamp: mercury dry-cell batteries
BATTERY-POWERED FLUORIMETER FOR DETERMINATION URANIUM 99

for portable instruments, and lead storage batteries for use in a 

laboratory, field station, or mobile unit.

Mercury batteries, recently developed, provide several times more 

current per unit volume than conventional dry cells. Batteries 

providing a starting voltage under load of 16 volts are available.

Performance tests of the batteries were made in which 500 milliamperes were drawn in the lamp circuit. Under continuous drain, 

the battery delivered this current for 90 minutes. After an overnight 

rest, an additional 50 minutes of service was obtained. Two such 

batteries, connected in parallel, provided 5 hours' service at the same 

current drain, followed by 1% hours' service after resting. This current 

drain represents an appreciable overload on the batteries and results 

in poorer performance compared to the rated capacity of 3000 ma-hr.

s-i \

R-2

FIGURE 15. Lamp circuit used In the Instrument. S-l, on-ofl switch; S-2, starting switch, normal position open; R-l, resistor, 16 ohms; R-2, variable resistor, 25 ohms; R-3, resistor, 60 ohms; E-4, resistor, 

24 ohms; B, battery, 12-16 volts.
100 METHODS OF ANALYSIS, URANIUM AND THORIUM

A storage battery is the most convenient power supply for the lamp 

where ease of portability is not important. The battery, only 18 inches 

long, consists of seven radio storage-type cells in series. The cells have 

transparent nonspillable polystyrene cases with built-in indicator 

floats. The dimensions of the unit cell are 2%e by 2% by 6 inches. 

The capacity of these cells is 26.5 ampere hours which is equivalent 

to about 50 hours of current-supply for the lamp per battery charge.

A voltage regulator is not required because the storage battery 

generally provides a steadier current than the voltage-regulated 

house current.

A convenient charging unit for the storage batteries consisting of 

a variable transformer, a selenium rectifier stack (output of 18 volts), 

and an ammeter was assembled. Convenient control of the charging 

rate can be obtained by varying the output voltage of the variable 

transformer.

The current flowing through the lamp circuit can be changed by 

varying resistance R-2 (fig. 15). Variation of the resistance produces 

a change in the light output of the lamp. This adjustment is employed for standardizing the overall sensitivity of the instrument. 

(Larger changes in the sensitivity may be made by changing the voltage on the photmultiplier tube as described below.)

Sample-support, filter, and shutter assembly. The arrangement of the 

sample-support, filters, and shutter is the transmission type previously 

described (part 12). The ultraviolet-lamp support seats directly on 

the Unit (fig. 16). The assembly is SO constructed that it may be 

used interchangeably with either the 5819 or the lP21 photOmultiplier tube. The primary filter is the Corning no. 5874 (2-inchsquare, polished thickness); the secondary filters consist of one each 

of Corning nos. 3486 and 9780 (2-inch-square) filters.

Photomultiplier tube and circuit. The 5819 photomultiplier tube 

is used in the instrument. The power source for the photomultiplier

tube consists of three 300-volt miniature "B" batteries in series. The

power circuit for the tube is shown in figure 17. With a total voltage

of 900 volts the amplification given by the iubc is about 200,000 times. 

The amplification may be doubled, as desired, by increasing the voltage 

to 1,000 volts. Switch 8 (fig. 17) provides for a stepwise application

of voltage tO the photomultiplier tube. Thus the tube may be operated over a considerable range of sensitivity. When leading tll6 

flUOr6SC6flCe dUling the analysis of a sample of unknown composition,

readings are taken at the lowest VolkgC flttd thfill 8.1 PlOgreSSiVelj 

higher voltages, if neCeSSftTy, tO aTOid damage^to the^photomultiplier 

tUbO, Ayeiftg6 anode currents of more than 750 microamperes Will

damage the tube. For maximum stability, thd BlOQe 

not exceed 100 microamperes.
BATTERY-POWERED FLUORIMETER FOR DETERMINATION URANIUM 101

HI lh

FIGURE 16. Reflecting support for the lamp. RS, reflecting shield; L, lamp; S, lamp socket; F, primary

filter holder.

 w

*»s, yw^ ot**2

U>

vw

IO 10 

I 

oc.

vVW,

FIGURE 17. Power circuit for the photomultipller tube. P, ROA photomultlpller tube 6819; M, mlcroammeter; S, selector switch; B, "B" batteries, 300 volts each; Rl-11, resistors, 1 megohm, M watt.
102 METHODS OF ANALYSIS, URANIUM AND THORIUM

As an alternative arrangement the 1P21 photomultiplier vtube may 

be used in place of the 5819 tube. The smaller size of the 1P21 tube 

is advantageous where maximum portability is desirable.

Microammeter. The currents generated by the photomultiplier 

tube are read directly with a micro ammeter. The meter in use until 

recently was a microammeter that gave full-scale readings of 4, 40, 

400, and 4,000 microamperes. Recently we replaced this with another 

meter having full-scale readings of 5, 15, 50, and 150 microamperes. 

The scales on this new meter give a convenient gradation of sensitivities within the useful range of the photomultiplier-tube output.

PERFORMANCE OF THE INSTRUMENT

The instrument gives good stability over a very wide range of 

sensitivity. At the sensitivities normally used, the instrument is 

standardized by adjusting the standard deflection (reading obtained 

with no sample in position and with the shutter open) to full-scale 

deflection on the most sensitive scale of the microammeter (4 microamperes) (part 11). This adjustment is made by varying the current 

supply of the ultraviolet lamp with resistance R-2 (fig. 15).

A standard curve for the instrument is shown in figure 18. The 

fluoride melts were prepared by techniques described hi parts 8 and 11 

and the melts were fused in specially designed platinum dishes (fig. 19).

0.025 0.050 0.075

MICROGRAMS OF URANIUM 

FIQUEB 18. Standard curve.

0.100
BATTERY-POWERED FLUORIMETER FOR DETERMINATION URANIUM 103

FIGURE 19. Platinum dish used for fusion.
104 METHODS OF ANALYSIS, URANIUM AND THORIUM

The ultraviolet lamp was powered by the storage-battery unit and 

the photomultiplier-tube voltage was 900 volts. The sensitivity is 

about 1 microampere for 0.01 microgram of uranium. As the meter 

can be read to the nearest 0.01 microampere on the 4-microampere 

scale, the sensitivity is adequate for this range of uranium concentrations.

The tabulation below shows the precision with which fluorescence 

measurements may be made with the fluorimeter. The fluorescence 

of melts prepared in the routine analysis of rocks for uranium was 

measured with the fluorimeter. Each melt was measured four times, 

and was rotated 90° between successive measurements. The overall 

variance of the measurements is 0.028,

Precision of fluorescence measurements

Sample

1...... ..... .... ........

2........ .. _ .......

3........ . ...........

4. ...................

6 __ ...................

6.-...... .........

7. ................ 

Scale

40

40

40

40

40

40

4

Headings (microamperes)

30.3, 30.4, 30.6, 30.7....... _ ..............

22.8, 22.8, 22.8, 22.9 _________ . ........

31.4, 31.6, 31.6, 31.8.. ......................

29.5, 29.5, 30.0, 29.4.. .............. ........

21.0, 21.4, 21.0, 21.1. _ ....................

24.7, 24.7, 24.8, 24.6. _ ....................

1.18, 1.18, 1.17, 1.20....... .................

Mean of 

readings

30.5

22.8

31.6

29.6

21.1

24.7

1.18

Variance

0.033

.0033

.027

.073

.037

.0067

.017

.028
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 14. SHORT ROUTINE DIRECT METHOD FOR THE 

FLUORIMETRIC DETERMINATION OF URANIUM IN 

PHOSPHATE ROCKS

By F. S. GRIMALDI AND NORMA S. GUTTAG

CONTENTS

Page 

Abstract._________________________________________________________ 105

Introduction._______-_____..._._.___._______..________.____..-__ 105

Experimental work________________________________________________ 106

Detailed procedure.__--__-__-___-__----_____-_-__-__-_____-_----_- 108

ILLUSTRATION 

FIGURE 20. Working curve..----------.-....___-_-_-_._.._....__.-. 109

ABSTRACT

A short routine direct fluorimetric procedure for the determination of as much 

as 0.06 percent uranium in phosphate rocks is described. The procedure employs 

a simple acid leach for preparing the solution, and the uranium is determined directly on a 1.8-mg aliquot. The results obtained by using this simple procedure on 

several thousand samples are discussed. The quenching of the uranium fluorescence by foreign elements was found to be negligible, for all practical purposes, 

and results on western phosphates may be corrected by using an empirically 

determined quenching factor.

INTRODUCTION

Need for faster routine uranium analyses of phosphate rocks made 

it necessary to reappraise previous methods for the purpose of introducing as many short cuts as possible consistent with the accuracy 

sought.

The fastest procedure used in the Geological Survey is the dilution 

technique that employs microgram amounts of samples in conjunction 

with very sensitive fluorimeters (part .8). This dilution technique 

is necessary for most types of materials to avoid quenching of the 

uranium fluorescence by foreign elements in the sample. However, 

microgram amounts of samples are unnecessary for the analysis of

NOTE. This report was Issued as Trace Elements Inv. Ropt. 134,1950.

268681 84 8 105
106 METHODS OF ANALYSIS, URANIUM AND THORIUM

phosphate rocks because in them the concentration of quenching 

elements is relatively small.

The use of larger samples has definite advantages for routine 

analysis because the ratio of fluorescence intensities to the blank 

value is greater. Consequently, variations in the blank value of ballmill ground flux result in no significant uncertainty hi the analysis. 

Also, a higher level of accidental contamination resulting from improperly cleaned glassware or airborne dust may be tolerated. The 

ideal direct method should employ a sample large enough to avoid the 

enumerated difficulties but small enough that quenching of the uranium 

fluorescence by foreign elements will not be significant.

In the preparation of the solution for analysis the complete decomposition of the sample is necessary. Lacking any information to 

the contrary it is the only safe procedure to follow. However, the 

uranium in phosphate rocks yields to simpler and faster methods of 

attack. The fastest solution procedure for a large number of samples 

is a simple acid leach. This method was investigated and gave 

excellent dissolution of all the uranium-bearing components of the 

rock.

The final procedure evolved for testing phosphate rocks integrates 

all the foregoing considerations and simplifications. An aliquot of the 

(18+82) nitric acid leach representing a 1.8-mg sample is evaporated 

in a 30-ml platinum crucible or other suitable container and fused 

directly over a burner with 3 g of fluoride-carbonate flux previously 

described (part 8). The fluorescence of the disc is measured in the 

reflection fluorimeter described by Fletcher and May (part 10).

These measurements may also be made with the transmission 

instrument (part 11).

EXPERIMENTAL WORK

Preliminary tests on about 30 samples indicated that the short 

procedure described in this paper was applicable to pkosptate rock.

Tk6 method was then adopted tentatively for routine uranium determination on phosphate rock. Several thousand samples typical of 

the deposits being tested by the Geological Survey were analyzed for uranium by this procedure oror m winded period <* time.

Concurrent with the chemical analyses, the uranium content of 

these samples was determined by independent methods. The results 

by beta-gamma count of total radioactivity were used as the main 

criteria for a "correct" analysis. This counting was done in the 

laboratory of the Geological Survey and has proved to be ft Very T6- liable DietllOll lor uranium aotormintvt/ivp« ^o^^o rooks.

About 10 percent of the samples counted were spot-checked by one
FLUORIMETRIC DETERMINATION OF URANIUM PHOSPHATE ROCK 107

or more of the refined chemical methods described by Grimaldi and 

Levine (part 6) and by Fletcher (part 8).

Data for the feasibility of simple acid attack were obtained by 

determining uranium in 100 samples by more conventional methods 

after complete decomposition of the sample and after simple acid 

leach. The acid-insoluble residues from 600 samples were also tested 

and found to be free from uranium.

The short procedure is not perfect by any means, but represents 

the best compromise at this time for speed, accuracy sought, simplicity, and convenience. Analysis of the results obtained with the 

short procedure on several thousand samples from the Florida 

phosphate deposits has shown that quenching of the uranium fluoresence by foreign elements has not been eliminated altogether.

1. In 90 percent of these samples the quenching amounted to less 

than 10 percent, and most samples showed no detectable quenching.

2. In 8 percent of the Florida samples the quenching was between 

10 and 20 percent; in most it was less than 15 percent.

3. The last 2 percent of the samples showed quenching of the order 

of 20 to 25 percent.

Phosphate rocks rarely contain more than 0.02 percent U, therefore errors due to quenching certainly can be tolerated, when they 

are of the magnitude cited. For example, a sample containing 0.015 

percent U would be reported as 0.012 percent U if the quenching 

amounted to 20 percent.

Analysis of the results obtained with the short procedure on more 

than a thousand samples of western phosphate deposits showed the 

following:

1. In 90 percent the quenching amounted to 15 percent or less; 

the average quenching in this group amounted to 12 percent.

2. In 8 percent the quenching amounted to 15 to 20 percent.

3. In the last 2 percent the quenching amounted to 20 to 25 percent.

Quenching is more serious in western phosphates, but it is also relatively constant in amount. Advantage may be taken of this to correct results on western phosphates by use of an empirical factor. 

The factor used in this laboratory is 1.18. Thus:

Percent U given by short procedureX 1.18="true" percent U.

The empirical correction factor was used to improve the results on 

500 more samples of western phosphates and the corrected figures 

were indistinguishable from results obtained by more reliable methods. 

Experience in our laboratory with simple acid leaching of phosphate rocks for the preparation of the solution for analysis has been
108 METHODS OF ANALYSIS, URANIUM AND THORIUM

very successful. Out of 4,000 samples of Florida and western phosphate deposits, only 4 samples so far have failed to yield completely 

to attack by (18+82) nitric acid. These four samples were unusual 

(the uranium-bearing mineral proved to be a different mineral than 

the one usually associated with phosphate rocks), but they yielded 

to attack by (1 + 1) nitric acid.

When thousands of samples have to be analyzed routinely by relatively unskilled technicians and speed is important, a certain fraction 

of the analyses reported will be in error no matter what procedure is 

used, and the irreducible minimum of errors will increase with the 

complexity of the analytical procedure. The results obtained here 

by this short procedure have been better on the whole than when 

more refined methods of analysis were used.

DETAILED PROCEDURE

1. Weigh out a 0.15-g sample into a 125-ml Erlenmeyer flask.

2. Add, by means of a graduate, 50 ml of carefully measured (18+82) HNOs.

3. Cover the flask with a small glass and heat the solution just to boiling on a 

hotplate. Boil gently for 2 minutes. Cool.

4. Take a 0.6-ml aliquot of the supernatant liquid by means of a 1-ml graduated 

pipette and transfer this amount to a clean 30-ml platinum crucible.

5. Evaporate the solution to dryness on the steam bath. Gently ignite the 

residue.

6. Add 3 g of the carbonate fluoride flux (9 parts NaF, 45.5 parts KjCOa, and 

45.5 parts Na 2COs by weight).

7. Heat on a low burner flame until the flux melts. The crucible should not be 

heated at any time above incipient red heat.

8. Heat for an additional 2 minutes at the lowest temperature at which the flux

stays molten, swirling and mixing the contents of the crucible to obtain a 

uniform melt. Place the crucible on an asbestos pad to cool and store in 

a desiccator for 30 minutes.

9. Read the fluorescence on the fluorimeter. Obtain the percent uranium by 

reference to the standard curve, figure 20.

10. For Florida phosphates, report what is obtained. For western phosphates, 

multiply the percent U by 1.18.
GALVANOMETER DEF

0.008 0.016 0.024 OX>32O'

PERCENT UBASEDON 1.8-mgSAMPLE

FIGURE 20. Working curve.

\

\

v

\

N

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 15. FLUORIMETRIG DETERMINATION OF URANIUM 

IN SHALES, LIGNITES, AND MONAZITES AFTER ALKALI 

CARBONATE SEPARATION

By NORMA S. GUTTAG AND F. S. GRIMALDI

CONTENTS

Introduction._____________________________________________________ Ill

Experimental data and discussion____________________._______________ 112

Procedure for shales and lignites____________________________________ 116

Procedure for monazite___________________________________________ 117

Results of analysis_______________________________________________ 118

TABLES

TABLE 1. Efficiency of the carbonate separation method under various test

conditions.____-___-___-_-_____-___-_-_-_____-_________ 114

2. Elimination of interference of copper with hydroxylamine hydrochloride -__-__--__-___--_______-_---__-__--__--_____.__ 115

3. Comparison of uranium analyses of shale by the carbonatefluorimetric procedure and by the uranyl nitrate extraction 

procedure____-___-_-_-_______-___-_-___-____-__^_____ 118

4. Comparison of uranium analyses of lignites by the carbonatefluorimetric procedure and by the uranyl nitrate extraction 

procedure__-___________________________________________ 118

5. Results of uranium analyses of monazites.___________-._-__-_ 119

INTRODUCTION

Comparative data are presented on separations of microgram 

amounts of uranium from milligram amounts of various metal ions 

with Na2C03-K2C03 , Na2C03-K2C03-H202 , and Na2C03-NaC10. 

The Na2C03-K2C03 separation procedure is applied to the analysis 

of shales, lignites, and monazites. This method will determine as 

little as 0.001 percent uranium in shales and lignites and 0.01 percent 

uranium in monazites.

Several fluorimetric procedures, based essentially on two techniques, 

have been developed in the Geological Survey and are used for the 

analysis of uranium in a wide variety of materials. One technique

NOTE. This report was issued as Trace Elements Inv. Kept. 153A, 1951.

Ill
112 METHODS OF ANALYSIS, URANIUM AND THORIUM

(part 6) involves a preliminary isolation of uranyl nitrate by solvent 

extraction from milligram amounts of sample. The second technique 

(part 8) based on Price's dilution method 1 involves no preliminary 

isolation of uranium and uses microgram amounts of sample. Each 

method has its advantages and disadvantages for routine work that 

need not be discussed here.

The Geological Survey is constantly searching for new methods or 

modifications that can be used in the determination of small amounts 

of uranium, even if applicable only to certain types of samples. This 

investigation of methods of analysis for uranium involves, among 

other things, evaluating known techniques and methods and devising 

new applications of known facts for special purposes.

Precipitation with alkali carbonate is a standard procedure for the 

separation of iron and other elements, that form insoluble hydroxides 

or carbonates, from uranium that stays in solution as a complex 

carbonate. It is a popular method of separation in procedures for 

the determination of macro amounts of uranium but is rarely used 

when micro amounts are to be determined. The neglect of this 

method in trace analyses is partly due to the lack of available data 

on the performance of this separation when small amounts of uranium 

are involved.

The purpose of this study was to obtain data on the carbonate 

separation method that might be applicable to work of the Geological 

Survey. The separation method was remarkably efficient and, in 

conjunction with fluorimetric estimation of uranium, provided the 

basis of a simple method for determination of small amounts (IX 10~8g

and more) of uranium in shales, lignites, and monazites. This

method will determine as little as 0.001 percent uranium, as the lower 

limit, in shales and lignite samples and 0.01 percent uranium as the 

lower limit in monazite samples.

EXPERIMENTAL DATA AND DISCUSSION

Preliminary tests were made to determine the efficiency of the 

carbonate separation of uranium from various metal ions. In these

tests sulfates of the test metals were used in amounts equivalent to 

15 rug or less of each metal oxide. This amount was determined by

the fact that the carbonate precipitation method proposed in this 

report uses solutions containing no more than 15 mg of each sample. 

The procedures used on the test samples follow:

In tKe first experiments (rn.eth.ocl. 1) a 5-ml aliquot of a. solution,

containing a known weight of metal sulfate, 0.05 ml of H2S04, and

i Price, 0. R.. Ferretti, R. J., and Schwartz, 8., 1945, The microfluorimetrio dQtermination of uranium: 

AECD 2282.
DETERMINATION URANIUM SHALES, LIGNITES, MONAZITES 113

2.257 of U, was transferred to a glass-stoppered test tube. Five 

milliliters of mixed carbonate solution (made by dissolving 10 g 

Na2C03 and 10 g of K2C03 in 100 ml of H20) were added from a 

pipette and the glass-stoppered tube shaken to give a uniform mixture. 

The tube was placed in a beaker of hot water for half an hour at a 

temperature of about 80 C. The tube was removed and the solution 

allowed to cool to room temperature for 1 hour. The solution was 

filtered through a dry filter paper (Whatman no. 42) and collected in a 

dry test tube. An 0.8-ml aliquot of the filtered solution was transferred to a platinum container (3.5-cm diameter) and the solution 

evaporated on the steam bath. Two grams of fluoride flux (9 parts by 

weight NaF, 45.5 parts by weight Na2C03 , and 45.5 parts by weight 

K2C03) were added and the mixture fused over a burner at a temperature not exceeding 700 C. Heating and mixing were continued for 2 

minutes after the flux melted. The fluorescence of the disc was then 

measured in a fluorimeter designed by Fletcher and May (part 

10). The carbonate precipitate was dissolved in HN03 and tested 

for occluded uranium by the uranyl nitrate extraction procedure 

(part 6).

In another set of experiments (method 2) the carbonate precipitation was made after the addition of 1 drop of 30 percent H202 to the 

test solutions that had been made as before. In still another set of 

experiments (method 3) the carbonate precipitation was made with 

5 ml of mixed carbonate solution containing 0.5 percent by weight of 

NaClO. The NaCIO was added to test the behavior of those elements 

that are oxidized to higher valence states.

Table 1 shows the results obtained. None of the low results obtained (method 1, Na2C03-K2CO3) was due to loss of uranium by 

occlusion in the carbonate precipitate but rather wa's due to quenching 

of the uranium fluorescence by the small amounts of the test elements 

escaping precipitation. Most of the carbonate filtrates were colored 

when low results were obtained.

Some additional observations relating to the data in table 1 should 

be pointed out. We note that the elements Y, Zr, V, As, Sm, and Gd 

are completely soluble and that Co, Ce, Nd, Pr, and Al are slightly 

soluble in carbonate solutions. This solubility is not due solely to the 

complexing action of carbonate. The amount of sulfate present in 

the solutions tested increased the solubility of some metals. For 

example, in the absence of sulfate, most of the zirconium is precipitated 

as well as most of the cobalt.
TABLI 1. Efficiency of the carbonate separation method un

Materials taken

Foreign element

0.5 mg CraOi-hfimg ZFeiOi- ......._ ...... ..__..--_--..._ __ .....

15 mg MeO.._.._._ ..... __ ...... _ ..... __ .. ___ . _______

lOmg ZrOs -. . .... . __ ..... __ .... .

10 mg VaOs ...... ..... -...._....... __ .. __ ... __ .....

15 mg MnO.-_.. _ ..... __ ....__ ...... __ .. _ - ___ .....

10 mg Co 0~- _....- .. _ . __-- ... __ .... . ____ .. _

6mg CoO+5 mgFeaOi.. . ..... __ ..... __ .. ___ .... .......

lOmgNiO. -...-._ .. -. - _ ..._. .- _ .... _ . ...

lOmgZtLO ... _ ..... _ ... ____ ... . __ . ___ __ .... ...

1 mg ZnO-f5 mg FeaOs..... __ .. __ ... . ___ . __ _ __ . .. ...

10 mg LajOj _ . _ ...... ____ ___ ... _ __ . ___ ___ .... ...

SmgYiOi ..... _..... -... ....... .......__.............

4 mg YaOj-l-5 mg FeaOi... ....... ...... ....... _ ...........

SmgCeaOj __ . _ ..... __ ..... _ .... __ ,. _ .. _ ..__ ....

10 mgN^iOt ...... __............. __ .. . ...... ...

lOmgPriOs--.. _ ........ ...... ...... .......... .............

lOmg SrnjOj... _ ...... ___ ... __ ..... __ . __ _ ____ . _ .

5 mg OdjOs. .....__ ..... .... . ....... __ .. __ _ ... ......

Uranium (7)

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.25

Apparent uranium recov

precipitation (NaaO

Method 1

2.25 

2.25 

2.25 

2.25 

2.25 

2.25 

2.22 

2.10 

1.05 

2.25 

2.25 

2.25 

2.25 

2.25 

2.22 

2.10 

2.25 

1.50 

1.50 

2.03 

1.95 

2.10 

2.10

Metho

(HjOs a
DETERMINATION URANIUM SHALES, LIGNITES, MONAZITES 115

Of the elements that are not precipitated, Y, Zr, V, As, Sm, Gd, 

and Al do not quench the uranium fluorescence. It might be generalized that the cerium earths are bad quenchers, whereas the 

yttrium earths do not quench the uranium fluorescence seriously. 

Mn, Co, and Cr are elements which apparently seriously quench the 

uranium fluorescence.

The behavior of copper (cupric) in the carbonate precipitation is 

erratic. In a few of our tests, copper was completely precipitated as 

CuO. However, the conditions for complete precipitation of copper 

appear to be exceedingly critical, and the precipitation is usually 

incomplete with much of the copper remaining hi solution as a blue 

complex. To insure complete precipitation, the copper can be reduced 

to cuprous oxide with hydroxylamine hydrochloride. This reagent is 

introduced only if a blue solution persists after the boiling with 

alkali carbonate.

The blue color of the soluble copper complex is barely perceptible 

at about 5Qy of copper in 10 ml of solution. Tests summarized in 

table 2 show that if the quantity of copper is insufficient to yield a blue 

color after the carbonate precipitation (that is, <507 Cu) no hydroxylamine need be added; this amount of copper will not result in 

any quenching of the uranium fluorescence using the general procedure. If hydroxylamine is used, the data in tables 2 and 3 show that 

no loss of uranium occurs by occlusion in the cuprous oxide precipitate. 

It has also been confirmed that the introduction of hydroxylamine 

causes no significant change in the behavior of the elements listed 

hi table 1.

The data in table 2 were obtained as follows: 5 ml portions of 

solutions containing 4.67 U (uranyl nitrate), varying amounts of 

copper sulfate, and 0.1 ml of (1 + 1) sulfuric acid were treated as 

previously described (p. 112, method 1). After heating for 10 minutes 

in the bath, 0.05 ml of a 20 percent aqueous solution of NH2OH-HC1 

(20 g per 100 ml of H20) was added to some of the samples. The heating was continued for 20 minutes for all the samples; they were then 

cooled for 1 hour. The uranium content was determined as before.

TABLE 2. Elimination of interference of copper with hydroxylamine hydrochloride

Materials taken

CuO

(7)

1.5.......

15........

75........

150.......

750.......

7500......

Uranium 

(7)

4.5 

4.5 

4.5 

4.5 

4.5 

4.5

NHsOH-HOl 

added (ml of 

20 percent solution)

0.05 

.05 

.05 

.05 

.05 

.05

Uranium 

found 

(7)

4.5 

4.5 

4.5 

4.6 

4.6 

4.6

Materials taken

OuO

(7)

None.... 

1.5 

7.5 . 

15 . .

75... 

Uranium 

(7)

4.5 

4.5 

4.5 

4.5 

4.5

NHjOH-HCl 

added (ml of 

20 percent solution)

0 

0 

0 

0 

0

Uranium 

found 

(7)

4.5 

4.6 

4.6 

4.7 

4.6
116

Of the three methods used to obtain data in table 1, fluorimetric 

results based on carbonate-peroxide separation (method 2) are 

poorest. The carbonate-hypochlorite method (method 3) is better 

than the simple carbonate method (method 1) for samples containing 

rare earths and would be the method of choice were it not for the 

serious interference of chromium. Of the elements tested in the 

simple carbonate method (method 1) only cerium, cobalt, and copper 

can interfere when uranium is determined fluorimetrically. The 

interference of copper is readily overcome by use of hydroxylamine.

In determining uranium in shales, lignites, and monazites the 

simple carbonate separation was selected for the following reasons:

1. Shale and lignite samples do not contain sufficient cerium or 

cobalt to interfere in a fluorescence method based on 1.2 mg of sample.

2. Although cerium normally would quench the uranium fluorescence in a 1.2-mg sample of monazite, the fact that the uranium content 

of monazite is usually greater than 0.1 percent enables us to use a 

sufficiently small sample (0.12 mg) to eliminate any quenching due to 

cerium. For the 0.12-mg sample used in the procedure for monazite, 

the smallest amount of uranium that may be determined without 

interference is 0.01 percent if the reflection fluorimeter is used and 

0.001 percent if the transmission instrument is used.

PROCEDURE FOR SHALES AND LIGNITES

1. Weigh 0.15 g of sample (minus 80 mesh) into a 70-ml platinum dish.

2. Ignite the sample gently to remove organic matter. Cool and 

moisten the sample with water.

3. Add 1 ml (1 -f-1) H2S04 and cautiously add 5-10 ml HF. Digest

sample on the steam bath and then evaporate the solution to PGDlOVe 

water.

4. Heat the sample until fumes of sulfuric acid evolve and allow

to fume for several minutes. Cool,

5. Cautiously add 25 ml of water, digest the sample on steam bath 

stirring to effect solution. Cool to room temperature.

6. Transfer the Contents of the dish to a 50-ml glass-stoppered 

graduated cylinder. Increase to 50 ml with water. Mix.

7. Take a 5-ml aliquot and transfer the solution to a 25-xnl glassstoppered test tube,

8. Add 5 ml of mixed carbonate solution (10 g Na2003 4-10 g 

BlaOOg per 1OO ml of wa/ter) and miv

9. PlftCG tlie StODpered tube in a beaker of not water and let stand

for so minutes at 80-90 C. If, after 10 minutes of heating, a blll8 

solution is evident, cool, add 0.05 ml Of 20 percent jh^drox^lamine 

hydrochloride solution (made by dissolving 20 g NH2OH-HC1 in 100 

ml H20) and resume the heating for another 20 minutes.
DETERMINATION URANIUM SHALES, LIGNITES, MONAZITES 117

10. Kemove the tube from the bath and allow the solution to cool 

for 1 hour at room temperature.

11. Filter part of the solution through a dry filter paper (Whatman 

no. 42) into a dry test tube. The filter paper may be conveniently 

held in place by the test tube itself. Instead of filtration, the precipitate is preferably centrifuged at 1700 rpm for 10-15 minutes.

12. Take an 0.80-ml aliquot and transfer the solution to a standard 

platinum container (part 13) and evaporate the solution on the steam 

bath.

13. Add 2 g of flux (9 parts by weight NaF, 45.5 parts by weight 

Na2C03 , and 45.5 parts by weight K2C03).

14. Heat over a burner until the flux melts and then for an additional 2 minutes, mixing and swirling the contents to assure a uniform melt. The temperature of the container should not be allowed 

to exceed 700 C during the heating period.

15. Place the dish on an asbestos pad to cool.

16. Measure fluorescence of the disc in the fluorimeter (part 10) and 

convert to percent uranium by reference to a standard curve. The 

standard curve is prepared by fusing various amounts of uranium 

with the fluoride flux and measuring the fluorescence intensity of the

discs.

PROCEDURE FOR MONAZITE

The procedure for monazite differs from the procedure for shale and 

lignite only in the method of preparing the solution and in the final 

size of sample taken.

1. Weigh 0.0800 g of representative finely ground monazite into 

a platinum crucible.

2. Add 0.6 g of flux (2 parts by weight NaF and 3 parts by weight 

K2S207).

3. Fuse the sample over a low burner until a clear melt is obtained 

(about 30 seconds). Cool.

4. Add 0.4 ml of concentrated sulfuric acid. Heat gently at a low 

temperature until all the fluorine is removed and a clear pyrosulfate 

melt is obtained. This fusion proceeds through several stages. In 

the first stage some frothing is apparent until the pad disintegrates. 

The melt is usually colored and muddy. In the second stage the 

melt thickens appreciably and becomes lighter in color. In the final 

stage a clear pyrosulfate melt is obtained. The total time for the 

complete process takes about 3K minutes. Cool.

5. Add 10-15 ml of water and 2 ml concentrated sulfuric acid. 

Digest the melt on the steam bath. Stir occasionally until the melt 

is completely disintegrated.

6. Transfer the sample to a 100-ml glass-stoppered graduated cylinder and increase to 100 ml with water. Mix. A complete solution
118 METHODS OF ANALYSIS, URANIUM AND THORIUM

generally is obtained within 5 minutes. Sometimes a cloud (presumably anhydrous rare-earth sulfates) persists after 5 minutes. 

This is not important as long as the sample has been completely 

decomposed.

7. Disperse the mixture by shaking. Immediately draw off a 5-ml 

aliquot and transfer to a glass-stoppered test tube.

8. Proceed according to steps 8-11 of the procedure for shales.

9. Take an 0.3-ml aliquot and proceed as in the procedure for shales 

steps 12-16.

RESULTS OF ANALYSIS

Tables 3, 4, and 5 list the results obtained by the carbonatefluorimetric procedure on shales, lignites, and monazites, respectively. 

The results for the shales and lignites agree closely with those obtained by the uranyl nitrate extraction procedure (part 6). The 

results on monazites agree with those obtained by colorimetric analysis (part 3). The carbonate precipitates from shales and lignites 

were also tested for uranium by the extraction procedure; uranium 

was not occluded.

TABLE 3. Comparison of uranium analyses of shale by the carbonate-fluorimetric 

procedure and by the uranyl nitrate extraction procedure

Sample no.

1.... .........

2.............

3.............

4......... .

5...... .

0.............

7...... ...... .

8 ..........

Analyses by 

Carbonatefluorimetric 

procedure 

(percent TJ)

0.006 

.008 

.005 

.007 

.005

.005 

.006 

.003

Uranyl 

nitrate 

extraction 

(percent XT)

0.005 

.008 

.005 

.006 

.006

.005 

.006 

.003

Percent 

uranium 

occluded 

by carbonate 

precipitate

0.000 

.000 

.000 

.000 

.000 

.000 

.000 

.000

Sample no.

9.............

10............ 11... ......

19

13'..........

141..........

15 i.. ........

16 i. .........

Analyses byCarbonatefluorimetric 

procedure 

(percent XJ)

0.005 

.004 

.005 

.004 

.003

.014

.005 

.003

Uranyl 

nitrate 

extraction 

(percent U)

0.005 

.005 

.005 

.004 

.003

.015

.005 

.003

Percent 

uranium 

occluded by carbonate precipitate

0.000 

.000 

.000 

.000

.000 

.000

.000 

.000

1 These samples are mineralized shales containing from 4 to 10 percent CuO. Results for uranium obtained by tie procedure using hydroxylamine hydrochloride.

TABLE 4. Comparison of uranium analyses of lignites by the carbonate-fluorimetric 

procedure and by the uranyl nitrate extraction procedure

Sample no.

I.............

3.... 

4.............

5...... .

6... - 

7... - 

8..... .....

Analyses by 

Carbonatefluorimetric

procedure

(percent U)

0.015 

.011 

.012 

.012 

.011 

.010 

.018 

.017

XJranyl 

nitrate extraction

(percent U)

0.016 

.011 

.011 

.013 

.011 

.010 

.016

.018

Percent

uranium occluded by carbonate

precipitate

0.000 

.000 

.000 

.000 

.000 

.000 

.000

.000

Sample no.

9............

10. _ .... _ -

11. _ ........

12............

13............

14..... . ......

15 .-. .

Analyses by 

Carbonatefluorimetric

procedure

(percent U)

0.018

.016 

.024 

.027 

.014 

.024 

.027

Uranyl 

nitrate

extraction

(percent U)

0.019

.015

.025 

.029 

.013 

.025

.029

Percent

uranium occluded 

by car- bonate

precipitate

0.000

.000

.000 

.000 

.000 

.000

.000
DETERMINATION URANIUM SHALES, LIGNITES, MONAZITES 119 

TABLE'S. Results of uranium'analyses*of monazites

Sample no.

1...... .................. .

2.. ................ .......

3.........................

4.........................

5.........................

6... ......................

Analyses by 

Carbonatefluorimetrlc 

procedure 

(percent U)

/ 0.39 

I .37 

/ .26 

I .26 

f .16 

I -17 

.38 

.26 

.35

Colorimetric ' 

method 

(percent U)

0.32 

.24

.16

.38 

.28 

.34

Sample no.

7.... ........ ........ ..

8... ..... ...........

10.-.. 

11-. 

12.. 

13... 

14......... ........

Analyses by 

Carbonatefluorimetric 

procedure 

(percent U)

0.67 

f .25 

I .26 

1.1 

.27 

.26 

.24 

.24 

.27

Colorimetric ' 

method 

(percent U)

0.64 

} .26

1.0 

.28 

.23 

.22 

.22 

.27

1 Analyst, Henry Mela, U. S. Geological Survey.

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 16. NONINTERFERENCE OF ARSENATE ION IN THE 

VOLUMETRIC DETERMINATION OF URANIUM USING 

THE JONES REDUCTOR

By JACK J. ROWE

CONTENTS

Page 

Abstract__---__-_.--__.-___.__..____._._.__._________.._._._-.-._ 121

Introduction. ____________________________________..-_.-___-___---___ 121

Experimental data_.-_----_-_-__-____________________________-_.___ 122

Apparatus and reagents___-_-_________-___________-_--.__.-...___ 122

Procedure..._____-.-.._..._.__._.-____________.._-_- 122

TABLES

TABLE 1. Consumption of permanganate after passage of arsenate ion

through Jones reductors and aeration____._-______._____-. 123

2. Lack of interference of arsenate ion in the volumetric determination of uranium using zinc amalgams___________________ 123

3. Effect of aeration on the consumption of permanganate.------ 123

ABSTRACT

Arsenate ions in sulfuric acid solution do not interfere in the volumetric determination of uranium if zinc amalgam reductors are used. Tests on zinc reductors amalgamated with 2, 3, and 10 percent, by weight, of mercury indicate that 

the arsenate ion is reduced slightly but this interference is almost eliminated 

during the aeration of the solutions after passage through the reductors and 

before titration.

INTRODUCTION

Most chemists consider that arsenic interferes in determining 

uranium and other elements that are commonly determined by means 

of reduction-oxidation reactions involving the use of zinc amalgams. 1 2

NOTE. This report was issued as Trace Elements Memo. Kept. 316,1951.

1 Hillebrand, W. F., and Lundell, Q. E. F., 1929, Applied inorganic analysis, p. 102, New York, John 

Wiley and Sons.

J Kolthoff, I. M., and Sandell, E. B., 1948, Textbook of quantitative Inorganic analysis, p. 599, New 

York, The Macmillan Co.

268681 54 9 121
122 METHODS OF ANALYSIS, URANIUM AND THORIUM

Many procedures for the volumetric determination of uranium make 

provision for the initial removal of arsenic by volatilizing it as the 

trichloride or tribromide or by precipitating it as the sulfide. 3 In the 

course of an investigation to determine the extent of arsenic interference, it was found that arsenate is not appreciably reduced in the 

reactions and does not interfere seriously in the volumetric determination of uranium.

EXPERIMENTAL DATA

APPARATUS AND REAGENTS

Jones redactors: 1. One filled with zinc amalgam containing 2 percent by

weight of mercury.

2. One containing 3 percent by weight of mercury.

3. One containing 10 percent by weight of mercury. 

The reductor tubes had a diameter of % of an inch, and 

the amalgam was packed in each to a column height 

of 12 inches.

Arsenate solution: Sodium arsenate solution was made by dissolving pure 

As2Oa in sodium hydroxide solution, acidifying with 

sulfuric acid, and oxidizing with permanganate solution using a trace of KIOs as a catalyst. The final 

solution contained 10 percent by volume sulfuric acid.

Uranium solution: This solution was made from UaOg (99.96 percent pure) 

(standard) fused with K2 S20? and the melt dissolved in 10 percent 

by volume H2SO4.

PROCEDURE

To determine whether arsenate would consume permanganate after 

passage through the Jones reductor and aeration, 50-ml volumes of

sodium arsenate solution, 10 percent by volume in sulfuric acid, were 

passed through the three reductors (2, 3, and 10 percent). Each solution Was then aerated for 5 minutes. After the addition of one drop

of 0.002M potassium iodate as a catalyst, the solutions were titrated 

with standard potassium permanganate, 0.03N. The results are 

given in table 1. We cannot conclude from these results that arsenate ion is not reduced at all. It is possible that some arsenate was

reduced to As+++ and subsequently reoxidized by air or that some

Was reduced to arsine and oxidized or removed from solution by the

air stream.

. n.ocicio«. oiomo»t j.. ioso. An.xiytioa.1 oiiomistry of the Manhattan project, p. 56, 138, 142, New York, 

McGraw-Hill Book Co., Inc.
NONINTERFERENCE OF ARSENATE VOLUMETRIC DETERMINATION 123

TABLE 1. Consumption of permanganate after passage of arsenate ion through 

Jones reductors and aeration

Reductor 

(percent)

2.............

3 ..........

Sodium 

arsenate 

taken, 

calculated 

as As (g)

0.05

.5 (')

.05

.5 (')

KMnO« 

(ml)

0.3

.3 

.1

.3

.3 

.05

Equivalent 

Ui08 (g) 

(corrected 

for blank)

0. 0008

.0008

.0008

.0008

Reductor 

(percent)

10...........

Sodium 

arsenate 

taken, 

calculated 

as As (g)

0.05

.5 

(0

KMnO« 

(ml)

0.2

.25 

.1

Equivalent 

UaO, (g) 

(corrected 

for blank)

0. 0004

.0006

' Blank.

To determine whether the presence of arsenate ions would interfere 

when uranium is determined by these methods, solutions were made 

containing various amounts of sodium arsenate and uranium in (1 + 9) 

sulfuric acid. Fifty milliliters of each solution were passed through 

the reductors. The solutions were then aerated for 5 minutes, one 

drop of 0.002M potassium iodate was added to each, and they were 

then titrated with permanganate. The results are shown in table 2.

TABLE 2. Lack of interference of arsenate ion in the volumetric determination of 

uranium using zinc amalgams

Reductor 

(percent)

3.............

UaOg taken 

(g)

0.05

.05 

.05 

.10 

.10 

.10 

.15 

.15

Sodium 

arsenate 

taken, 

calculated 

as As (g)

None

0.05 

.5 

None 

.05 

.5 

None 

.05

0.03N 

KMnO« 

(ml)

11.70

11.90 

11.90 

23.50 

23.75 

23.75 

35.10 

35.00

Reductor 

(percent)

10... 

UjOs taken 

(g)

0.05

.05 

.05 

.10 

.10 

.10

Sodium 

arsenate 

taken, 

calculated 

as As (g)

None

0.05 

.5 

None 

.05 

.5

0.03N 

KMn04 

(ml)

11.70

11.76 

11.80 

23.40 

23.40 

23.40

To determine the influence of aeration on the consumption of 

permanganate, four separate arsenate solutions were passed through 

the 3-percent reductor. Two of the solutions were aerated and two 

were not before the titration with permanganate. The results of this 

experiment are given in table 3.

TABLE 3. Effect of aeration on the consumption of permanganate

Solution no.

1 _ ...................... _ ............

2......... ...............................

3............ ......... ..................

Sodium

arsenate

taken,

calculated

as As (g)

0.1

.1

.5

Procedure

0.03N

KMnO*

(ml)

0.25

.60

30

2 An
124 METHODS OF ANALYSIS, URANIUM AND THORIUM

This experiment shows that some reduction of arsenate ion is obtained (solutions 2 and 4) but that the interference is minimized by 

aeration. It would be of interest to determine the actual valence 

state or states of the reduced arsenic. As aeration, an essential step 

hi the volumetric determination of uranium, eliminates interference 

by the reduced forms of arsenic, no attempt was made to pursue the 

problem.

It would be reasonable to assume that:

1. Most of the arsenate is not reduced. This was indicated qualitatively by the formation of a sulfide precipitate (subsequent to the 

passage of arsenate through the reductors) with hydrogen sulfide at 

an acidity favorable for the precipitation of arsenic pentasulfide and 

unfavorable for the precipitation of arsenic trisulfide. Furthermore 

the size of the precipitate indicated that arsenic had been completely 

recovered.

2. Little if any of the arsenate is reduced to the trivalent state. 

Were this to occur, a high consumption of the permanganate would 

be obtained in the unaerated solutions. It is also doubtful that air 

could oxidize trivalent arsenic hi 10 percent (by volume) sulfuric acid 

solutions.

3. A small amount of the arsenic is reduced to arsine. This would 

account for the small titration obtained in the unaerated solutions. 

The smaller titration obtained after aeration could be explained by 

mechanical removal of arsine by air. The small residual titration 

obtained after aeration is probably due either to the incomplete 

removal of arsine or to the slight oxidation of arsine to the arsenite 

during the aeration.

4. Arsenate is not reduced to metallic arsenic. This was indicated

by the lack of darkening of the reductors even after the passage of

more than 5 g of arsenic.
BULLETIN 1006. COLLECTED PAPERS ON ANALYSIS FOR URANIUM

AND THORIUM

Part 17. THE FLUORIMETRIG DETERMINATION OF 

URANIUM IN NONSALINE AND SALINE WATERS

By AUDREY PIETSCH SMITH and F. S. GRIMALDI

CONTENTS

Page 

Abstract.....-_.-.._-._-_-..._._---_----..------..._.._-----..-.-- 125

Introduction._____________________________________________________ 126

Experimental data __._______________________._..___.._______._--- 126

Nonsaline waters._____________________________________________ 127

Saline waters__-___-_-_-__-_-___---___-____-_--__.__--_----_- 127

General procedure for the determination of uranium in nonsaline and 

saline waters.-_________________---__-_____----_-__--__________-- 130

Sampling.._..-.--.-.__._.-_.---..-----_--..-...-_----.-.-.--. 130

Procedure..-._-_-__.__-___._.-_-__________---__.__---_.--_---. 130

Literature cited__.--._______-..__._-_----.-_.__-____._____--_---_ 131

TABLES

TABLE 1. Uranium found in distilled water after the addition of known

amounts of uranium._____-__-_____-__-___________-___-- 128

2. Comparison of results of two methods of fluorimetric uranium

determination of naturally occurring nonsaline waters.------ 128

3. Uranium analyses of synthetic sea-water solutions containing

known amounts of uranium._____________________________ 128

4. Test of procedure on a sea-water sample from the surf at Ocean

City, Md..-.-.--......------.-.........-...-..-.--_.-- 129

5. Uranium found in sea water from Ocean City, Md., after addition

of known amounts of uranium..._________________________ 129

6. Uranium found in water samples from the coast of Florida.-..- 129

ABSTRACT

The procedure determines about 10~8 percent uranium using 500-ml samples 

of water. Uranium is concentrated by precipitating uranyl phosphate using 

aluminum phosphate as a carrier. The aluminum phosphate is dissolved in nitric 

acid, salted with aluminum nitrate, and the uranium is extracted with ethyl 

acetate. A portion of the ethyl acetate is evaporated in a standard platinum 

dish and a fluorescing disc is prepared with a mixed fluoride flux. Fluorescence 

measurements are made with a fluorimeter. One precipitation with aluminum 

phosphate collects more than 95 percent of the uranium. The uranium content 

of various ocean waters tested ranged from 2.3X 10~7 to 3.4X 10~7 percent uranium.

NOTE. This report was issued as Trace Elements Inv. Kept. 181,1962.

125
126 METHODS OF ANALYSIS, URANIUM AND THORIUM

INTRODUCTION

In the determination of uranium in waters containing slightly more 

than 10~8 percent uranium, it is frequently necessary to concentrate 

the uranium before its estimation by the fluorescence method using 

fluoride phosphors. The uranium in waters of low salinity can be 

concentrated by simple evaporation of the water, but this method is 

not as useful for saline waters, where the problem is not only to concentrate the uranium but to separate it from large amounts of salts 

that would cause subsequent analytical difficulties.

Hernegger and Karlik (1934) isolated uranium from sea water by 

precipitating the uranium with ammonium hydroxide using a small 

amount of ferric iron as a carrier. This carrier has also been used by 

others (Lahner, 1939; Hoffman, 1939; and Urry, 1941) for concentrating uranium from rocks and from ocean sediments. Other useful 

collectors for uranium include aluminum hydroxide (Urry, 1941, and 

Orlemann, 1945) and aluminum phosphate (Tschernichow and 

Guldina, 1934).

Aluminum phosphate has certain advantages as a carrier for 

uranium. Especially important is the ease with which aluminum 

phosphate can be dissolved with dilute acids even after it is aged or 

ignited. We have found aluminum phosphate to be an efficient 

collector even for less than microgram amounts of uranium.

This paper presents a simple fluorimetric method for the determination of uranium in naturally occurring waters. Preliminary concentration of uranium is made by precipitating uranyl phosphate using 

aluminum phosphate as the carrier. After dissolving the aluminum 

phosphate in nitric acid and salting the solution with aluminum 

nitrate, the uranyl nitrate is isolated by extraction with ethyl acetate 

(part 6). The relative fluorescence of the disc is measured in a

fluorimeter (partlO). The procedure is designed to determine 10~°g 

of uranium as a lower limit and uses 100- to 500-ml samples of water.

Tlie procedure recommended is based on two operations the

coprecipitation of uranium with aluminum phosphate, and the isolation of uranyl nitrate by ethyl acetate extraction from solutions

salted with aluminum nitrate. The reliability of the extraction

process lia,s l>oe±i de:m_o:n.s't:r'a,'te<i axxd is a, sta^da/i'd. prooodiiro ua. tlio

laboratory of the Geological Survey for the isolation of uranium

from many naturally occurring materials before the estimation of 

uranium by the fluorescence method. The major aim is to show

that aluminum phosphate is an efficient collector for uranium,

Data on the efficiency of aluminum phosphate as a carrier for uranium were obtained by several more or less independent techniques.
FLUORIMETRIC DETERMINATION NONSALINE, SALINE WATERS 127 

NONSALINE WATERS

The following techniques were used in testing nonsaline waters:

1. Known amounts of uranium were added to separate 500-ml 

aliquots of distilled water. Analysis for uranium was then made 

according to the recommended procedure of this report. The recoveries obtained are given in table 1, column 3.

2. The amount of uranium left in the filtrates after the precipitation and filtration of the aluminum phosphate was determined. This 

was accomplished in the following manner: The filtrates were evaporated to dryness and the ammonium salts were destroyed by aqua 

regia. Chlorides were converted to nitrates by evaporation with 

nitric acid, and the nitric acid solutions obtained were extracted with 

ethyl acetate after adding the requisite amount of aluminum nitrate 

for salting. The uranium in the ethyl acetate layers was determined 

fluorimetrically and the results corrected for the small amount of 

uranium introduced by the reagents are given in table 1, column 4. 

The tests on the filtrates show that more than 95 percent of the 

uranium is collected by the aluminum phosphate. Some samples, 

table 1, showed slightly low overall recoveries of uranium. These 

errors are inherent in the fluorimetric procedure. For instance, it is 

sometimes difficult to burn the ethyl acetate without a slight loss. 

Some quenching of the uranium fluorescence occurs because platinum 

may be dissolved from the fusion vessel. This may occur if there is 

accidental overheating during the preparation of the standard disc.

3. Naturally occurring waters were used in 500-ml aliquots and 

uranium was determined by alternate methods. In one method the 

procedure of this report was used. In the other, concentration of 

uranium was made by simple evaporation of the water and the 

uranium was extracted directly without prior precipitation with 

aluminum phosphate. The results by the two methods are given in 

table 2. The agreement is close and differences are no greater than 

the reproducibility of either method.

SALINE WATERS

In testing saline waters, the following techniques were used:

1. To 500-ml aliquots of a synthetic solution made to approximate 

the composition of ocean water known amounts of uranium were 

added. Uranium was then determined by the recommended procedure, and the amounts found are given in table 3.

2. In another set of experiments, actual ocean waters were used. 

Quadruplicate uranium determinations were made on a sample of 

water obtained from the surf at Ocean City, Md. (table 4). The 

filtrates from the aluminum phosphate precipitates were further 

treated as follows: On filtrates 1 and 2 the aluminum phosphate precipitation was repeated and the precipitate analyzed for uranium to
128 METHODS OF ANALYSIS, URANIUM AND THORIUM

determine if the second precipitation would recover more uranium. 

Known amounts of uranium were added to filtrates 3 and 4, the 

aluminum phosphate precipitation repeated, and the precipitate analyzed for uranium. The results of determinations on these four filtrates are given in table 4. The results of tests on Ocean City water 

after the addition of known amounts of uranium are given in table 5.

Table 6 gives the location and uranium content of waters collected 

off the coast of Florida.

The uranium content of the Ocean City water and the waters from 

the Gulf of Mexico is greater than the content generally found in 

other ocean waters by earlier investigators (Hernegger and Karlik, 

1934, and Koczy, 1950). This may be a purely local condition. Our 

results are in line with the recent results of Nakanishi (1951).

TABLE 1. Uranium found in distilled water after the addition of known 

amounts of uranium

Sample no.

I...... .......

2._.....__....

3... __ ......

4.............

5... . 

6. __ . __ ...

7..... -

Uranium 

added (micrograms)

0.09

.09

.30

.45

.45

1.2

1.8

Uranium found i 

(micrograms)

0.11

.09

.32

.44

.40

1.4

1.6

Uranium 

found in 

filtrates 

from AlPOi 

separation (micrograms)

<0.01

<.01

.02

.01

Sample no.

8.............

9.............

10............

12............

13............

Uranium 

added (micrograms)

1.8

9 n

9 0

18

36

36

Uranium found ' 

(micrograms)

1.7

8.3

8.5

34

qc

Uranium 

found in 

filtrates 

from AlPOi 

separation (micrograms)

0.01

<.01

1 In samples 7-13 a correspondingly smaller aliquot of the ethyl acetate extract was used for the determination of uranium because the normal aliquot yields fluorescence intensities beyond the range of the working 

curve.

TABLE 2. Comparisons of results of two methods of fluorimetric uranium determina' 

tion on naturally occurring nonsaline waters

Sample no.

i.. __________

Percent uranium, 

A1PO4 concentration of uranium

2.8X10-« ..... 

5.2X10-0.....

Percent uranium ' 

no Al P O4 concentration 

of uranium

3.0X10-«. 

4.6X10-«.

Sample no.

3.. ___ .-----...... 

4__ ____ _________

Percent 

uranium, 

A1PO« concentration 

of uranium

1.1X10-0-....

2.8X10-' .....

Percent 

uranium ' 

no A1PO« 

concentration 

of uranium

l.lXlO-o. 

3.0X10-'.

i Analyst, A. M. Sherwood. U. S. Geological Survey.

ATH.E 3. Uranium analyses of^ synthetic sea-water solutions containing known

Sample no.

i. _ ......... _ .. _ .

2......... -

3......... ... .... ... ...

4....... ...............

Uranium added 

(micro- grams)

0.36

.72

1.80

1.80

Uranium round

(micro- grams)

0.35

.70

1.77

1.79

Sample no.

5............ .............

6.... ___ ... ... __ . ..

7.........................

Uranium added

(micrograms)

1.80

3.60

3.60

Uranium found (micrograms)

1.80

3 Oft

3.34
FLUORIMETRIC DETERMINATION NONSALINE, SALINE WATERS 129 

TABLE 4. TesJ of procedure on a sea-water sample from the surf at. Ocean City, Md.

Sample no.

1... ....... ................ ....:....: 1

2........................................

3..... ...I. .-.. .' .....:...

4........................................

Filtrate from 1 _____ ., ___ ..'...-.

Filtrate from 2 ..........................

Filtrate from 3.... _ ....... __ ... _ ..

Filtrate from 4 ..........................

Uranium 

added (micrograms) '

0: .

0

. . ' 0 - ' 0o 

0

 ' .'45

1.80

Uranium found (micrograms)

1.1.....-. _. .._::._. i......

1.2.. ..................................

1.1...-.....-,..,....-..... .........

1.2....- .....-.... . . 

. - 1

 : ! : .' ..

Uranium 

found in 

2dAlPOi 

precipitation 

 (micrograms)

 0.-01

.01

.48

1.74

TABLE 5. Uranium found in sea water from Ocean City, Md., after addition of 

known amounts of uranium.

Test no.

1.. ... ... ................ ..

2...... ....

3.... ................. ........

4... .............. ............

5 __ ..-..-...-... __ ...... __ -

6.. ;. - 

7..... .......................... .

8.- ...........................

Amount of. 

sea water ' 

taken 

(ml)

600 

. 500 

500 

500 

5(10 

500, 

500 

500

Amount of uranium (micrograms)

Present in 

the sea 

. . . water.

1.15 ,,:.i.i5

1.15 

1.15 

1.15

; . 1. 15

1.15 

1.15

' Added

0.90 

.<00 

2.2 

2.2 

9.0 

9.0 

18 

18

 Total 

. present

2.05 

2.05 

3.35 

3. 35 

10.15 

10.15 

19. 15 

. 19. 15

Total 

found

2.1 

1.9 

3.1 

3.1 

9.5 

9.6 

18 

18

TABLE 6. Uranium found in water samples from coast of Florida (Gulf of Mexico 

and near the Indian River estuary) 1 

Sample no.

1. ....... ......... _.... . ... .

2... ............... .....................

3... .................................

4. ... . -

Location

Latitude

26°31' N. ...

26°39' N_ .

28°1.5'N 

28°2.5' N 

Longitude'

83°10' W. _ 

82°31' W...... 

80°32.5' W.....

80°32.2' W....'.

Depth of 

 water ' . 

(fathoms)

25 

11 

5 

8

Uranium 

(percent)

3.2X10-'. 

3.4X10-'. 

3.0X10-'. 

3.0X10-'.

Filtrates from samples 1 and 3

1 ___ . _____ _ '-. .................... . __ .. _____ '.... ____ ....

3.. ... ...-....... . ... ..... ....... ................

Micrograms of uranium

Added

1.35 

1.35

Found

1.35 

1.35

> Collected by Albert Collier, U. S. Fish and Wildlife Service. 

* Surface samples.
130 METHODS OF ANALYSIS, URANIUM AND THORIUM

GENERAL. PROCEDURE FOR THE DETERMINATION OF 

URANIUM IN NONSALINE AND SALINE WATERS

SAMPLING

In sampling waters it is good practice to add acid (about 8 ml of 

nitric acid per gallon of water) immediately after collection. If the 

water sample contains sediment, the sediment should be separated 

by decantation or by filtration through a porous filter before adding 

acid to the water. Unacidified water samples tend to decrease in 

uranium concentration during storage because some of the uranium 

may be precipitated or adsorbed on the glass (Koczy, 1950).

PROCEDURE

1. Transfer a 500-ml aliquot of water to an 800-ml beaker.

2. Add 3 ml of HNO3 , aluminum nitrate solution equivalent to 

20 mg A12 03 , and 5 ml (NH4) 2HP04 solution [1 cc= 12 mg (NH4) 2HP04]. 

Heat to boiling to remove C02 .

3. Add ammonium hydroxide until methyl red indicator is just 

yellow.

4. Digest the precipitate on the steam bath for about 10 minutes. 

Stir in paper pulp.

5. Filter the solution on a fast paper and wash the precipitate with 

1 percent NH4N03 solution.

6. Transfer the precipitate and paper to a clean 25-ml porcelain 

crucible and ignite at low temperature to remove carbon.

7. Add 5 ml of (15+85) HNO3 1 and warm gently to dissolve the 

salts (avoid significant evaporation of the solution).

8. Add 9.5 g A1(NO3 ) 3 -9H2O and warm to dissolve the salt.

9. Pour the solution into a dry 30-ml glass-stoppered graduated test 

tube. Do not wash the crucible.

10. Add 10 ml of ethyl acetate by pipette or buret and shake the 

mixture for about l to 2 minutes. Allow the layers to separate for a

few minutes.

11. Filter about 8 ml of the ethyl acetate through a dry Whatman 

no. 42 filter paper into a dry test tube.

12. Transfer a 2-ml aliquot (more or less may be necessary depending on the uranium content of the water) of the filtered ethyl acetate

into a standard platinum container, part 13. Place tlie disn on four

layers of water-soaked paper that rest in a pan containing about Ke

inch of water and ignite the ethyl acetate with a lighted splinter. 

After the ethyl acetate has burned off, evaporate the residue on

1 Present practice is to use 5 ml of (7+93) HNOs (part 1, extraction method).
FLUORIMETRIC DETERMINATION NONSALINE, SALINE WATERS 131

13. Add 2 g of the mixed fluoride flux (prepared by grinding or 

mixing together 9 parts NaF, 45.5 parts Na2C03 and 45.5 parts 

K2C03 , by weight).

14. Heat over a burner until the flux melts and then for an additional 2 to 4 minutes, mixing and swirling the contents to assure 

a uniform melt. All heating should be done at the lowest temperature 

at which the flux stays molten. The temperature of the melt should 

not be allowed to exceed 700 C during the heating period.

15. Measure the relative fluorescence of the melt with afluorimeter.

LITERATURE CITED

Hernegger, F., and Karlik, B., 1934, Die quantitative Bestimmung sehr kleiner

Uranmengen und der Urangehalt des Meerwassers: Akad. Wiss. Wien,

Math.-naturwiss. Kl., Sitzungsber., Abt. Ila, 144 Band, p. 217. 

Hoffman, J., 1939, Uran in Gesteinen und Sedimenten des Erzbesbirgsbruches:

Akad. Wiss. Wien, Math.-naturwiss. KL, Sitzungsber., Abt. Ila, 148 Band,

p. 189. 

Koczy, Gerta, 1950, Weitere Uranbestimmungen an Meerwasserproben: Akad.

Wiss. Wien, Math.-naturwiss. KL, Sitzungsber., Abt. Ila, 158 Band, 1-5

Heft, p. 113-122. 

Lahner, I., 1939, Uran und Thorium Bestimmungen an Kalken und Dolomiten

und die Frage des radioaktiven Gleichgewichtes in diesen Gesteinen: Akad.

Wiss. Wien, Math.-naturwiss. KL, Sitzungsber., Abt. Ila, 148 Band, p. 149. 

Nakanishi, M., 1951, Fluorometric microdetermination of uranium. V. The

uranium content of sea water: Chem. Soc. Japan Bull., v. 24, no. 1, p. 36. 

Orlemann, E. F., 1945, Progress report, Clinton Engineering Works, CEW-TEC

CD 2244. 

Tschernichow, J. A., and Guldina, E., 1934, Colorimetrische Bestimmung von

Uran in uranarmen Erzen: Zeitschr. anal. Chemie., v. 96, p. 260. 

Urry, W. D., 1941, The radioactive determination of small amounts of uranium:

Am. Jour. Sci., v. 239, p. 191-203.

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 18. THE GEOLOGICAL SURVEY PHOSPHATE-FLUORIDE-IODATE METHOD FOR THE DETERMINATION OF 

VERY SMALL AMOUNTS OF THORIUM IN NATURALLY 

OCCURRING MATERIALS

By F. S. GRIMALDI and J. G. FAIRCHILD

.' CONTENTS .......

: Page 

Abstract____--_-----_:______-__ ________-_._____ ___------___ _. 134

Introduction.- _ ________ J_ _ i i-j_ ____ _1 _ ___ ^ __ _ __-.__ ___'_-__ __....--___ 134

Outline of procedure________;_____ .....1...^..................... 135.

Discussion of general procedure_^___i_.,______-____________ _ _______ 135

Discussion of special procedure-wl^____.___i_i__.______.-'_ --------._ 138

General procedure.________________________________________________ 139

The chemical concentration of thdriumiL 1 __ _ .1................... 139

.The estimation of thorium___-_________________._____-----__-___- 141

Method'A. Nephelometrically as the iodate._l._____--_-----__ 141

Method B. Photometrically with p-dimethylaminoazophenylarsonic acid_'._..___._ i;___,i^ i _^ i _____-___--__._ 142

Method C. Gravimetrically .with ammonia and peroxide.______ 142

Special procedure for monazite._____________________________________ 143

Experiments._ ________1_______ ____________________________________ 144

1. Analysis of synthetic mixtufesJ_j____________;_______-__-_l_--_ 144

2. Occlusion of rare earths with the phosphate precipitate.________'_ 146

3. Failure of hydrofluoric acid separation of thorium from zirconium

in the presence of alkaline earths and alkalies,__.___.__-_-_____ 147

4. Nonocclusion of zirconium, titanium, and iron by thorium fluoride

when mercurous chloride is used as carrier__ _ _______________ 147

5. Optimum conditions for the precipitation of thorium with p-dimethylaminoazophenylarsonic 'acid :_.. _ __-___ ^ _.: i '_ _______ . ... 148

6. Interference of oxidizing agents in .the photometric determination

of thorium ___________________ __,________:.___ _i___ ________ 149

7. Spectral transmittancy and standard curves for the; photometric determination of thorium with p-dimethylaminoazophehylarsonic 

acid_______:______ij____L:_'___J_-l::____;____J__'__-- _._ 149

8. Irihomogeneity of the. reagent p-dimethylaminoazophenylarsonic

acid.....____,__,__,.________u.-.______--^_-_____ 149

Literature cited__ .................j___j_____^_i____^____-_-_^__. 152

NOTE. This report was Issued as Trace Elements inv. Kept. 31E arid AECD 2632,1946.

133
134 METHODS OF ANALYSIS, URANIUM AND THORIUM

ILLUSTRATIONS

Page

FIGURE 21. Spectral transmittancy curve for the determination of thorium with p-dimethylaminoazophenylarsonic acid_-__-__._ 150 

22. Fisher electrophotometer readings for the photometric determination of thorium with p-dimethylaminoazophenylarsonic 

acid.____-_-____--_________--___-__-_---_-___-__-____ 151

^ TABLES

TABLE 1. Analysis of synthetic mixtures______._.____-__-____-_____. 145

2. Analysis of synthetic mixtures..__-__-______-______--____.__ 146

ABSTRACT

Detailed procedures are presented for the determination of very small percentages of thorium. The methods are designed to determine 0.001 percent of 

thorium oxide as the lower limit and are applicable to silicate and phosphate 

rocks. For quantities below 1 mg of thorium oxide, the thorium is determined 

nephelometrically as the iodate or photometrically with p-dimethylaminoazophenylarsonic acid. For quantities of thorium above 1 mg of thorium oxide, 

the thorium is determined gravimetrically. A discussion of the important features of the methods and a summary of the more important experimental work 

that led to the adoption of the procedures are given.

INTRODUCTION

In the work of the Trace Elements project of the U. S. Geological 

Survey it was necessary to know the thorium content of samples for 

which measurements of total radioactivity and uranium content had

been made. Methods had to be developed by which accurate determinations of very small percentages of thorium could be made on 

rocks and ores of widely varying types. This report presents some

of the procedures developed in the chemical laboratory of the Geological Survey that are now in use.

In any method for the determination of thorium, the thorium must 

be separated from other elements, of which titanium, zirconium, and

rare eartlxs are particularly troublesome. In addition, ft Suitable

means of measurement is required for quantities of thorium less than

l mg. The problem is complicated by tne wide variety of materials 

to be analyzed, which included many types of rocks, and metallic and

nonnxetaUic ores. Tlxe laigli p>lxosj>lia-te content of some samples £as

much as 35 percent PjOj) is particularly troublesome. The methods

found in the literature were found wanting in one or more respects. 

These methods are outlined, with some discussion, by Hillebrand

undell {ld2?J, The thiosulfate ^Fresenius and Hintz; 1896,

p. 525) and peroxide (Wyrouboff and Verneuil, 1898, p. 340) separations fail in the presence of phosphate. The precipitation of thorium
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 135

as fluoride and as iodate are used under conditions modified from those 

in the literature. Thus, in the iodate method (Meyer, 1911, p. 65), 

the acidity recommended in the literature is too high for complete 

precipitation of small amounts of thorium.

The procedure given below is complex and slow. However, it can 

be simplified considerably for the analysis of less complex materials 

than those dealt with by us.

OUTLINE OF PROCEDURE

The essential features of the method are as follows:

1. Complete decomposition of the sample. It cannot be assumed 

that no thorium is present in undecomposed material.

2. Precipitation of thorium phosphate using zirconium or titanium 

as carrier, the precipitation being made at an acidity of 0.3N hydrochloric acid. (Separation from the bulk of constituents.)

3. Concentration of thorium as fluoride by two treatments with 

hydrofluoric acid, mercurous chloride being used as carrier. (Separation from titanium, zirconium, iron, niobium, tantalum, and phosphate.)

4. Solution of the thorium fluoride in sulfuric acid.

5. Precipitations as thorium iodate. (Separation from rare earths.)

6. Estimation of thorium (a) nephelometrically as the iodate, or

(b) photometrically with p-dimethylaminoazophenylarsonic acid, or

(c) gravimetrically with ammonia and hydrogen peroxide.

In the general procedure monazite and rare-earth mineral concentrates yield large fluoride precipitates that tend to occlude small 

amounts of zirconium. If the first hydrofluoric acid precipitate is 

large, the procedure is modified by changing the order of the separations. The precipitations as iodate are interposed between the first 

and second fluoride precipitations. The rare earths are thus removed 

before the final hydrofluoric acid precipitation and a better separation of the zirconium is obtained. (Special procedure for monazite.)

DISCUSSION OF GENERAL PROCEDURE

Separation. The sample is completely decomposed and a hydrochloric acid solution of the sample is made (part 2). Use of sulfuric 

acid or bisulfate fusions in preparing the solution is avoided if much 

calcium is present, as with phosphate and carbonate rocks, because 

any calcium sulfate precipitated will interfere with the isolation of 

thorium. Any insoluble products, such as hydrolytic precipitates of 

tantalum, niobium, tin, titanium, zirconium, tungsten, especially in 

the presence of phosphate, will carry down thorium and so must be 

kept with the solution during the analysis, or if filtered off should be 

combined with the phosphate precipitate when it is burned (step 7).
136 METHODS OF ANALYSIS, URANIUM AND THORIUM

The phosphate precipitation (step 5) is made in 0.3N hydrochloric 

acid solution. Under these conditions, thorium is coprecipitated with 

zirconium or titanium phosphate and with some iron phosphate. 

Thorium is separated from moderate amounts of rare earths by this 

treatment (Experiments, 2). If the rare earths in the sample exceed 

about 10 mg of oxides, a part of the rare earths may be coprecipitated.

If the sample contains heavy metals, an acid hydrogen sulfide separation should be made before making the phosphate precipitation.

The phosphate precipitate is burned and treated with hydrofluoric 

acid to dissolve the phosphates of zirconium, titanium, and iron, and 

all the hydrolytic precipitate. Thorium is converted to the insoluble 

fluoride. If the total amount of fluoride. precipitate obtained is less 

than a few milligrams,, mercurous chloride is precipitated from the 

solution to serve as a bulky carrier for the thorium fluoride precipitate. 1 Other carriers that were tried occluded titanium and zirconium; 

thus with calcium fluoride, as much as 6 percent of the zirconium 

added was coprecipitated. It was hoped that sodium fluoride would 

inhibit the precipitation of zirconium by stabilizing the fluozirconate 

ion, but we found that the coprecipitation of zirconium with the calcium fluoride was greatly increased by the addition of sodium fluoride 

(Experiments, 3). The amount of zirconium and titanium carried 

down by mercurous chloride is less than 0.01 mg of each as found by 

spectrographic analyses (Experiments, 4). The ease of filtration of 

mercurous chloride and its easy removal are further advantages.

The precipitate of mercurous chloride may be dark. This is probably because minute amounts of platinum, or possibly gold, palladium, 

selenium, tellurium, and arsenic are reduced to the elemental condition on the surface of the. mercurous chloride. (Pierson, 1934, p. 

437.)

The mercurous chloride is volatilized, leaving the concentrate of 

thorium fluoride in the crucible. Caution is necessary to avoid loss

of thorium by dusting, .both while burning and wetting the fluffy

residue. The thorium fluoride should be heated to a low temperature

to prevent the formation of the less soluble thorium oxide. The 

usual precautions must be taken against mercury poisoning. A

second precipitation as thorium fluoride ensures the removal of the

last traces of titanium and zirconium; tne residue then contains little

impurity except possibly a little lead fluoride and some rare-earth

fluorides or oxides. . . 

The thorium fluoride is converted to sulfate; any eerie ion formed

in the ignition of the fluoride precipitate is reduced by adding sul1 Mercurous chloride Is not a carrier in the accepted sense of the word. Its sole function is to provide

bulk. If the thorium fluoride has not already precipitated, the mercurous chloride will serve no useful 

function. If the thorium fluoride has precipitated out, the mercurous chloride is a convenient collector of 

the thorium fluoride.
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 137

furous acid. Any lead present is precipitated and filtered off. The 

excess sulfuric acid is then removed because it interferes with the 

precipitation of thorium iodate. In removing free sulfuric acid, care 

must again be taken to prevent the formation of thorium oxide by 

overheating.

The thorium sulfate is dissolved in nitric acid and the thorium 

separated from any remaining traces of rare earths by precipitation 

as thorium iodate. It may be directly determined nephelometrically, 

or further treated and determined photometrically with ^-dimethylaminoazophenylarsonic acid, or determined gravimetrically as thorium 

oxide.

The photometric method of determination has the advantages of 

greater objectivity and reproducibility than the nephelometric method, 

but the latter is simpler and more direct. However, the stability of 

the cloud of thorium iodate may be markedly affected by the presence 

of small amounts of impurities. For example, a few tenths of a 

milligram of zirconium causes very rapid clotting of the iodate precipitate, leading to low results nephelometrically.

The iodate precipitation may not be necessary for samples containing less than a few milligrams of rare-earth oxides (Experiments, 

2). The thorium may then be determined directly by the photometric method by adjusting the acidity and adding y-dimethylaminoazophenylarsonic acid. Other such simplifications and shortened 

procedures will occur to the analyst dealing with materials of more 

restricted composition than those provided for here.

Determination as thorium iodate. The cloud of thorium iodate is 

stable enough for nephelometric estimation up to 0.7 mg thorium 

oxide. There is a good spread from zero to 0.3 mg thorium oxide, 

0.05 mg being readily detected. A drop of hydrogen peroxide is 

added to insure against the presence of quadrivalent cerium, which 

would also precipitate as iodate. If the sample contains at this point 

more than a few milligrams of rare earths, the thorium must be further purified by filtering and dissolving the iodate in nitric acid and 

reprecipitating as the iodate.

Determination with p-dimethylaminoazophenylarsonic acid. The 

precipitation of thorium by p-dimethylaminoazophenylarsonic acid is 

quantitative from buffered solutions such as acetate solutions. The 

acidity must be controlled (Experiments, 5). The reagent is not 

very specific, as it precipitates to some extent many elements (such 

as zirconium, titanium, rare earths, uranium, and iron) at this acidity. 

However, the thorium obtained by the procedure has been freed from 

interfering elements.

The iodate precipitate is dissolved in hydrochloric acid and the 

solution evaporated. Strong oxidizing agents that are released

268681 54 10
138

would disturb the photometric determination and are here removed 

by sulfurous acid (Experiments, 6). The acidity is adjusted and the 

thorium is precipitated by the dye. The precipitate is filtered and 

washed to remove excess dye. The arsonic acid precipitate of 

thorium could be ignited to thorium oxide and weighed. For 

photometric determination, the precipitate is decomposed on the 

filter with dilute sodium hydroxide solution, releasing dye equivalent 

to the amount of thorium in the precipitate. The relation between 

the amount of dye precipitated with the thorium and the amount of 

thorium present is exact and reproducible. Other applications of 

^-dimethylaminoazophenylarsonic acid in colorimetry are shown 

by Hayes and Jones (1941, p. 603) and Nazarenko (1937, p. 1696).

The dye solutions closely follow Beer's Law up to about 0.45 mg 

thorium oxide and the standard curve is reproducible for even larger 

amounts (Experiments, 8). If the weight of thoria exceeds 0.5 mg, 

it is better to dilute so that the sample is in the range of Beer's Law.

We found that the commercial p-dimethylaminoazophenylarsonic 

acid reagent is likely to be inhomogeneous; not only does it vary 

from lot to lot, but different parts of the same lot may vary in composition. A new standard reference curve should be made with 

every new solution of the arsonic acid reagent, even when successive 

batches are made from the same bottle of reagent (Experiments, 9). 

The experiments show that if the dye is not completely dissolved, the 

residue differs in composition from the material in solution.

Gravimetric determination. If the thoria content exceeds 1 mg, as 

indicated by the size of the iodate precipitate, the iodate precipitate 

is dissolved in hydrochloric acid and the thorium precipitated with 

ammonia in, the presence of hydrogen peroxide. The precipitate is

filtered and ignited to thorium oxide. The peroxide provides a 

delicate test for the presence of cerium. If the precipitate shows

discoloration, it is best to filter without washing, redissolve in nitric

acid., and. reprecipitate as iodate.

DISCUSSION OF SPECIAL PROCEDURE

The general procedure must be modified for the analysis of samples, 

such as monazite, that have a high content of rare earths. These 

yield large precipitates of rare-earth fluorides at step 8 of the general

procedure that tend to occlude zircon.iu.irx. For example, tlie analysis

of a monazite by the general procedure gave 10.40 percent thorium 

oxide, by the special procedure 10.02 percent thorium oxide, the 0.38 

percent difference was found spectrographically to be due to the

presence of zirconium.

The special procedure differs from the general procedure only in 

the order of the separation steps. After one fluoride precipitation,
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 139

the rare earths are removed by repeated iodate precipitations, then 

the second fluoride precipitation is made to remove the last traces of 

zirconium. The special procedure is included in this report to illustrate these principles; simpler methods for the determination of 

thorium in monazite are given in parts 19 and 20.

GENERAL PROCEDURE

THE CHEMICAL CONCENTEATION OP THORIUM

Special reagents:

Potassium iodate, 7% percent solution.

Mercurous nitrate solution, 8 mg HgCl equivalent per ml.

Dissolve 0.952 g of reagent-grade mercurous nitrate in water

containing a few frops of nitric acid and adjust the volume to

100 ml with water.

1. For samples containing less than 0.04 percent thorium, take 5.00g, 

proportionally less for samples of higher thorium content. Prepare 

a hydrochloric acid solution of the sample as outlined in part 2. Any 

hydrolytic precipitate should be left in the solution, or if filtered 

should be added to the phosphate precipitate when it is burned 

(step 7).

2. Evaporate the solution to dryness to eliminate the free acid.

3. With a pipette add 10 ml of (1 + 1) hydrochloric acid solution. 

Digest about 15 minutes on the steam bath and then add 130 ml of 

water. Digest until the soluble salts are dissolved.

4. While stirring, slowly add 10 ml (1 ml=2 mg Zr02 ) of zirconium 

nitrate solution. 2 Warm to about 90 C.

5. Add 4 g of diammonium phosphate dissolved in about 20 ml of 

water. Dilute with water to 200 ml. Cover the beaker and digest 

on the steam bath for at least 4 hours.

6. Add paper pulp, stir, and filter on an 11-cm S and $ 589 white 

ribbon filter paper. Wash with 4 percent ammonium nitrate solution.

7. Transfer the filter paper with precipitate to a porcelain crucible. 

Burn gently, starting at a low heat and gradually raising the temperature until the carbon is burned off.

8. Transfer the residue to a 100-ml platinum dish or crucible. 

Moisten with a little water and add 20 ml of hydrofluoric acid. 

Cover with a platinum cover and digest until soluble constituents 

dissolve. Evaporate the sample on the steam bath until about 8 ml 

remain. Add 10 ml of hydrofluoric acid and evaporate again to 

about 8 ml. Dilute with 30 ml of water. Warm on the bath. If

* In this procedure zirconium phosphate formed in step 5 acts as a collector for the thorium phosphate. 

Alternately the zirconium may be omitted and the acidity of the solution after the addition of ammonium 

phosphate (step 5) carefully adjusted with ammonium hydroxide until a fair-sized phosphate precipitate 

is obtained from the still acid solution.
140 METHODS OF ANALYSIS, URANIUM AND THORIUM

less than a few milligrams of fluoride precipitate is obtained, proceed 

to step 9. If more than a few mg of fluoride precipitate is obtained, 

omit step 9 and proceed to step 10.

9. Add 10 ml of the mercurous nitrate solution. Next add 1 ml 

of dilute hydrochloric acid (7 + 100) and stir with a platinum rod. 

Warm on the bath for a few minutes and then allow to stand at room 

temperature for about 4 hours, keeping the dish covered.

10. Filter on a no. 40 Whatman 9-cm filter paper in a hard rubber 

funnel and wash twice with 10 to 15 ml of approximately 5 percent 

hydrofluoric acid wash solution, making the wash solution directly in 

the dish that contained the precipitate and scrubbing the inside of 

the dish thoroughly with a rubber policeman wetted by the solution. 

Wash twice with water.

11. Transfer the paper and precipitate to a 20-ml platinum crucible, 

shield from drafts and burn gently below 500 C hi a well-ventilated 

hood until the paper is burned off and the mercurous chloride volatilized. The precipitate must be burned carefully and slowly; if the 

mercurous chloride is volatilized too fast, thorium may be lost by 

dusting. Also, burning at too high a temperature may convert some 

of the thorium fluoride to thorium oxide which is harder to dissolve.

12. Carefully moisten the fluoride residue with a few drops of water. 

Add about 8 ml of hydrofluoric acid. Cover the crucible and digest 

on the steam bath for 20 minutes. Transfer the contents of the 

crucible to a platinum dish. Wet and scrub the inside of the crucible 

thoroughly with a rubber policeman, rinsing into the dish. Dilute 

with water to 40 ml. Add 10 ml of mercurous nitrate solution, 

warm, add 1 ml of dilute (7 + 100) hydrochloric acid solution and stir. 

Let stand at room temperature for about 4 hours.

13. Filter on a no. 40 Whatman 9-cm filter paper in a hard rubber

funnel and wash twice with hydrofluoric acid wash solution and twice 

with water.

14. Transfer the paper and precipitate to a small (20 ml) platinum

crucible and again carefully burn at below 500 O in. a well-ventilated

hood until the paper is burned off and the mercurous chloride is 

volatilized.

15. Wet the residue in the crucible with a few drops of water; dry

on the steam bath. Carefully add 0.5 ml of sulfuric acid. Allow to

fume on the hotplate for about 15 minutes, keeping the crucible 

covered. Cool. Cautiously add water until the crucible is about

three-fourths full. Add a few drops of 6 percent sulfurous acid solution to decolorize any quadrivalent cerium, and evaporate until

water is removed. Bring to fumes of sulfuric acid and fume 15 

minutes. Cool. Add about 10 ml of water and transfer the contents 

to a 50-ml beaker. Police the crucible and wash with water, adding
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 141

the washings to the beaker. At this point, the volume of the solution 

should be 25 to 30 ml. Warm gently, then allow to stand for about 

4 hours.

16. Filter off any lead sulfate on a no. 42 7-cm Whatman paper and 

wash a few times with 1 percent sulfuric acid solution. Collect the 

filtrate in a 50-ml platinum dish.

17. Evaporate the solution nearly to dryness and then bring to 

fumes. Drive off all the free sulfuric acid at a low temperature. This 

is conveniently done by heating on a hotplate until dry and then 

rotating the dish above a low bunsen flame until no more fumes appear. 

The temperature should be kept below 450 C to avoid formation of 

thorium oxide, which in the next step may not dissolve completely in 

the nitric acid. The removal of free sulfuric acid is essential because 

excess sulfate interferes with the precipitation of thorium iodate 

(step 19).

18. Add 6 ml of (1 + 1) nitric acid solution from a pipette. Add 1 

drop of 30 percent hydrogen peroxide, warm gently and then add 10 

ml of water. Cover the dish and digest on the steam bath for a few 

minutes until the thorium is dissolved.

19. Transfer with a jet of water to a 100-ml beaker, policing the 

dish thoroughly. Adjust the volume to 42 ml with water. Cool to 

room temperature. Add by pipette 8 ml of 7K percent potassium 

iodate solution. If less than 1 mg of thorium is indicated by the 

cloud of thorium iodate, the thorium may be determined either 

nephelometrically as the iodate (step 20), or photometrically with 

^-dimethylaminoazophenylarsonic acid (step 21); and if more than 

1 mg thorium oxide is present, determine it gravimetrically (step 28).

THE ESTIMATION OF THORIUM

METHOD A. NEPHELOMETRICALLY AS THE IODATE

20. Let the thorium iodate precipitate stand 15 minutes (30 minutes 

for ThC>2 content of 0.1 mg or less) and compare against a series of 

standards containing known amounts of thorium with the same 

amounts of nitric acid and iodate in the same volume, and prepared 

at the same time as the unknown sample.

If the iodate precipitate indicates a thorium content greater than 

0.3 mg and less than 1 mg thorium oxide, an aliquot is taken, as 

follows, without filtering off the thorium iodate. Add 12 ml of (1 +1) 

nitric acid solution to dissolve the thorium iodate. Transfer one-third 

of the solution into another 100-ml beaker. Adjust the volume with 

water to 45 ml and add 5% ml of 7% percent potassium iodate solution 

from a graduated pipette. Match against a series of standards. The 

match is made by placing the beakers on a dark plate in front of a 

window and looking into the beakers.
142 METHODS OF ANALYSIS, URANIUM AND THORIUM

METHOD B. PHOTOMBTRICAIXY WITH p-DIMETHYLAMINOAZOPHENYL,-

ARSONIC ACID

Special reagents :

p-Dimethylaminoazophenylarsonic acid solution. Dissolve 0.1 g 

of the finely powdered reagent in 50 ml of (1 + 1) alcohol 

solution containing 10 g of ammonium acetate. Filter.

Buffered wash solution. Dissolve 10 g ammonium acetate and 

12 ml of (7 + 100) hydrochloric acid solution in 488 ml of water.

21. Let the thorium iodate precipitate stand overnight. Filter on 

a 7-cm no. 42 Whatman paper. Do not wash.

22. Dissolve the iodate precipitate off the filter with alternate 

washes of hot (1 + 1) hydrochloric acid solution and hot (7+100) 

hydrochloric acid solution, three portions of each. Collect the filtrate 

in the same 100-ml beaker that contained the iodate precipitate.

23. Evaporate to dryness on the bath. Add about 8 ml of fresh 6 

percent sulfurous acid and evaporate to dryness again.

24. Dissolve in 4 drops of hydrochloric acid and 43 ml of water. 

Add 2 drops of methyl red indicator and neutralize with ammonia 

until the methyl red turns yellow. Add dropwise a solution of hydrochloric acid (7 + 100) until the methyl red just turns red. Add 1.2 ml 

excess. Now add 5 ml of a solution of ^-dimethylaminoazophenylarsonic acid. Cover the beaker and allow to digest on the steam bath 

until the precipitate clots (10 to 20 minutes).

25. Filter on a 10-ml asbestos Gooch filter and wash 4 times with 

10-ml portions of the ammonium acetate wash solution.

26. Pour over the Gooch filter 30 ml of a warm 4 percent solution 

of sodium hydroxide and collect the washings in a clean receiver. 

Wash once with water.

27. Make the filtrate up to 250 ml. Read the optical density on a 

filter photometer using a blue filter or on a spectrophotometer at 460 

millimicrons (Experiments, 7). Obtain the thoria equivalent by 

reference to a standard curve (Experiments, 8).

If tkere is more tkan 0.5 mg TnO2 , it is better to make the dilution

so that the sample is in the range of Beer's Law. The standard 

curve should be checked at intervals; two known concentrations 

usually are enough.

28. If the thoria content exceeds 1 mg, the determination is made 

gravimetrically. Allow the iodate precipitate (step 19) to stand

overnight. Filter on a 7-cm no. 42 Whatman paper, bub do not

wash. Dissolve the iodate precipitate off the filter with alternate 

washes of hot (1 + 1) hydrochloric acid solution and hot (7+100) 

hydrochloric acid solution, three portions of each. Collect the filtrate in the same 100-ml beaker that contained the iodate precipitate,
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 143

Evaporate the solution to dryness. Add 5 drops of hydrochloric 

acid and 15 to 20 ml of water. Warm and add 1 drop of 30 percent 

hydrogen peroxide; neutralize with ammonia, adding a few drops of 

ammonia in excess. Digest on the steam bath about 15 minutes, 

add paper pulp and filter on a no. 40 7-cm Whatman paper. Wash 

with 4 percent ammonium nitrate solution. Ignite to thorium oxide 

and weigh.

SPECIAL PROCEDURE FOR MONAZITE

29. Fuse 0.5 g of finely ground sample in a porcelain crucible with 

3 g of sodium peroxide. Cool the melt and transfer to a 250-ml 

beaker containing 100-150 ml of water. Add hydrochloric acid in 

excess and evaporate to dryness. Dissolve with dilute hydrochloric 

acid and filter, reserving the filtrate. Gently ignite the residue in 

platinum and volatilize the silica with hydrofluoric acid and sulfuric 

acid. Remove excess sulfuric by fuming the sample to dryness on 

the hotplate. Sinter the residue with a little sodium carbonate, 

cool, leach with dilute hydrochloric acid, and add the total to the 

reserved solution. Make an ammonium hydroxide precipitation 

with about 2 ml of excess ammonium hydroxide, clot precipitate on 

steam bath and filter, washing with 0.1 percent ammonium chloride 

solution made alkaline to phenolphthalein. Burn the precipitate 

gently in a platinum dish and proceed to steps 8-11, inclusive, of the 

general procedure.

30. To the ignited fluoride precipitate in the platinum crucible 

add 1 ml of sulfuric acid, cover, and gently simmer the sample on the 

hotplate for about 20 minutes. The rare-earth fluorides are slowly 

attacked by this fuming with sulfuric acid. Cool, add a little water 

and transfer the mixture to a 100-ml beaker. Add a few drops of 

sulfurous acid to reduce cerium and evaporate the solution on the 

steam bath. Cover the beaker and allow the sample to digest overnight. This overnight digestion generally converts the fluorides to 

the soluble sulfates. In the morning, add water, and if a complete 

solution is not obtained, filter. Reserve the filtrate. Gently ignite 

the residue and treat again with sulfuric acid and heat until fumes 

evolve. These steps are repeated until a complete solution is 

obtained.

31. Evaporate the solution in a platinum dish on the steam bath 

to remove water. Cover the dish and place on a hotplate raising the 

dish slightly by a porcelain ring so that the bottom of the dish is not 

in actual contact with the hotplate. When the sulfuric acid fumes, 

remove cover and evaporate to dryness. Remove the last traces of 

excess sulfuric acid by heating gently over a burner at low heat (the 

temperature should not exceed 450 C).
144 METHODS OF ANALYSIS, URANIUM AND THORIUM

32. Add 6 ml of (1 + 1) nitric acid, 2 drops of 30 percent hydrogen 

peroxide, and 10 ml of water, and digest on the steam bath a few 

minutes keeping the dish covered. A complete solution will be obtained at this point. Transfer the solution to a 100-ml beaker and 

adjust the volume to 42 ml with water. Cool. Add 8 ml of 7^ percent potassium iodate solution and let stand for 1 to 2 hours.

33. Filter off the iodate precipitate. The iodate precipitate is 

dissolved, and enough iodate precipitations are made from nitric acid 

solutions to remove completely the rare earths (four will generally 

suffice). To test the complete removal of rare earths, add excess 

ammonia and a few drops of 30 percent hydrogen peroxide to the 

filtrate from the iodate precipitation. The rare earths show their 

presence as insoluble yellow hydroxides, the yellow is due to cerium.

The analyst must use his judgment on how to dissolve the iodate 

precipitates for reprecipitation. If the iodate precipitate is small, it 

may be dissolved off the filter paper with 6 ml (1 + 1) nitric acid so 

that precipitation becomes relatively easy. For monazite samples, 

the iodate precipitate is generally too large to be handled in this 

manner. The iodate is dissolved off the filter paper with a minimum 

of hot (1 + 1) hydrochloric acid solution. As the iodate precipitations 

must be made from nitric acid solution, the hydrochloric acid is next 

eliminated by precipitating the thorium with excess ammonia and

peroxide. The precipitate is filtered but not washed. It is dissolved 

off the filter with QYz ml of (1 + 1) nitric acid and reprecipitated with 

ammonia and peroxide. The second ammonia precipitate is sufficiently free from chloride so that after solution in 6.5 ml of (1 + 1) 

nitric acid, the solution is adjusted to 42 ml with water, a few drops

of 30 percent hydrogen peroxide and 8 ml of 7^ percent potassium 

iodate solution are added to give the second iodate precipitation.

34. Dissolve the final iodate precipitate off the filter with hydrochloric acid. The hydrochloric acid and the reduction products of

the iodate are next removed by precipitating thorium with ammonium hydroxide plus hydrogen peroxide. The ammonia precipitate 

is then gently ignited in a 100-ml platinum dish.

35. Add hydrofluoric acid and repeat the fluoride precipitation as

before (steps 8-11). The thorium fluoride obtained at this point 

should be free from all contaminants.

36. Dissolve the thorium fluoride in sulfuric acid and add a few 

drops of 30 percent hydrogen peroxide and precipitate with 1 to 2 ml

excess of ammonia. Ignite and weigk.

EXPERIMENTS

l. Analysis or syntnetlc mixtures

The methods described above were tested by analysis of solutions 

whose thorium content was not known to the analyst. The standard
PHOSPHATE-FLUORIDErlODATE METHOD FOR THORIUM 145

thorium solution was made from reagent-grade thorium nitrate that 

contained less than 0.1 percent of any other metal as determined 

spectrographically. The solution was standardized by evaporating 

to dryness and igniting to oxide, and by precipitating with ammonia 

and peroxide and igniting to: oxide.

The solutions for analysis' were made by adding .various amounts 

of thorium nitrate to 50 ml of either of two stock solutions. All 

reagents used were evidently free enough from thorium for the purpose, because the results with solutions of the lowest thorium contents analyzed were not significantly higher than the amount of 

thorium added. The synthetic stock solutions, labeled solution S 

and solution P, were made so that 50 ml of solutions S and P contain 

the following:

AljOi..... ...... ..............

MgO--. . ... ............

CaO.. .................................

KjO.. .. . ............

TiOi.... - ............. ................

ZrOs..-.... .-_. . . .............

V,0»... ................ .......

CrjOt.....-.-. .. ............... ........

MnO. ...... .. ......... ...........

BaO... . ... . ......L- .

PbO.._... . ............................

PjO!....... .... .:.:...... .... ....

YsOi...... .. _ ...... ..............

CeOi. ........ ... ......... .............

NiO. ........ ...... .......................

Solution S 

(grams)

0.75

.50

.05

.50

.30

.05

.005

.02

.02

., '.005

.005

.005

.005

%010

.005

;005

Solution P 

(grams)

0.20

.20

.05

1.60

.20 '.OS

«.005

.02

.02

.005

.005

.005

.005

. 1.25 '.01

'.01

.005

. .005

Salt used

Potassium dicbromate.

Cerous nitrate.

These solutions were added separately just before the analysis was begun.

Table 1 gives the analytical results obtained.

TABLE 1. Analyses of synthetic mixtures

Sample no.

P2

P3.......-. .-...... .......

P4._.....-. .... . ................

P6...._ - .- .....

O4Q7....._.:..: ......._. ....... PI........... ...................

HI. ...............................

J2.. ...... ................. ........

O2

P4......... ..... ................

H2.. ..............................

Ol

J6... ..............................

Q8.................................

Q5.......-r ... ..................

J4... .- .- :. .--.-.-.-..._.

Q3. . ...,-., ............_.....

Q6.. ..............................

Type 

sample

S

P

S

s

s

p

p

p

s

s

s

p

p

s

s

p

p

s

p

Th6> 

taken 

(mg)

0.05

.10

.25

30

30

.50

.55

.60

.70

.90

.90

.95 i nn

1.10

1.60

. 1.70

1.80

3.30

: 5.40

ThOa found 

nephelometrically 

(mg)

0.07

.09

.27

.20

 .70

..55 .'66

.80

1.0

.70

1.1

1.0

ThOj found 

photometrically 

(mg)

0.07

.10

.26

.23

' .66 '

.80

.87

1.04

ThOj found 

grayimetrically 

(mg)

1.1

1.5

 . 1.9

1.9

2.6

5.2
146 METHODS OF ANALYSIS, URANIUM AND THORIUM

The procedures were further tested by analysis of eight synthetic 

mixtures by W. G. Schlecht. The results given in table 2 indicate 

what might be expected on a first trial by an analyst unfamiliar with 

the procedures. Probably the discrepancies in the photometric results for samples S6 and S6 are caused mainly by imperfect separation of zirconium, which can cause small positive or negative errors 

in the nephelometric determination and larger positive errors in the 

photometric determination. Additional data applying this method 

to ores are given in parts 20 and 21.

TABLE 2. Analyses of synthetic mixtures

Sample no.

86........... ......................

SI.......... ....................

S3.................................

S8.................................

85.................................

S7_. ...............................

84.................................

S2... ..............................

Type 

sample

P

S

P

S

P

S

P

S

ThOj taken 

(mg)

0.00

.10

.25

.40

.65

.80

1.20

1.45

ThOj found 

nephelometrically 

(mg)

0.18

.10

.3

.35

.7

.6

1.0

ThOj found 

photometrically 

(mg)

0.52

.65

1.25

ThOj found 

gravimetrically 

(mg)

1.40

2. Occlusion of rare earths with the phosphate precipitate

To 50 ml of solution P, which contains 10 mg Y203 and 10 mg 

CaO, 0.95 mg (A), 0.25 (5) and 0.6 mg (C) of ThO2 were added. 

These were analyzed according to the procedure through step 16. 

Precipitation with excess ammonia in the presence of a few drops of 

30 percent hydrogen peroxide gave the following weights when 

ignited;

(A) 3.4 mg (B) 2.3 mg (C) 2,5 mg

The ignited oxides were dissolved and the thorium content determined nephelometrically as the iodate. The thorium contents found

(A) 1.1 mg Th02

(B) .36 mg ThO2

(C) .66mgTh02

The samples showed therefore the following quantity (mg) of rareearth oxides occluded:

(A) 2.3 mg

(B) 1.9 mg

(C) 1,8 mg

When the experiments were repeated with solution S that contained only half the amounts of rare earths in solution P, no rare 

earths were found to accompany the thorium.
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 147

3. Failure of hydrofluoric acid, separation of thorium from zirconium In the 

presence of alkaline earths and alkalies

To each of four platinum dishes were added 50 mg of zirconium 

oxide as the pyrophosphate, 0.3 mg thorium oxide as the nitrate, and 

60 mg calcium chloride. The mixtures were evaporated to dryness 

and 20 ml of hydrofluoric acid solution was added to each. After 

digestion the solutions were evaporated to 8 ml and then 10 ml of 

hydrofluoric acid added. The solutions were evaporated again to 8 

ml and then diluted with water to 50 ml and allowed to stand at 

room temperature for 4 hours. They were then filtered and washed 

with 4 percent hydrofluoric acid solution. The residues were burned 

in platinum and dissolved by fuming with perchloric acid. The solutions were diluted with water and exactly 100 mg of alumina (as the 

chloride) was added to each. Ammonia was now added until the 

solutions were neutral to methyl red, and the precipitates obtained 

were ignited and weighed. The weights of the ignited precipitates 

were 0.1032, 0.1031, 0.1029, 0.1031 g. The excess of about 3 mg was 

found to be due to zirconium.

In another series, 0.5 g sodium fluoride was added in addition to 

calcium in an effort to fix the fluozirconate ion, but the results were 

even worse than above as about 10 percent of the final ignited precipitate was zirconium oxide.

4. Nonoccluslon of zirconium, titanium, and Iron oy thorium fluoride when 

mercurous chloride is used as carrier

To each of four beakers were added 50 mg zirconium oxide as the 

nitrate, 50 mg titanium oxide as the chloride, 1 g ferric oxide as the 

chloride, and 0.5 mg thorium oxide as the nitrate. A phosphate 

precipitation was made according to the procedure outlined in step 5. 

After filtration, the phosphate precipitates were burned and treated 

with hydrofluoric acid, as in step 8.

The thorium fluoride was filtered off with the aid of 80 mg of mercurous chloride as carrier. The fluoride precipitate was dissolved 

with fuming sulfuric acid, exactly 100 mg of alumina was added and 

an ammonia precipitation made. This was filtered off, burned and 

examined spectrographically by J. C. Kabbitt for zirconium, titanium, 

and iron. The results obtained with only one hydrofluoric acid 

treatment are as follows:

No.

1. ........... ........ .....

2................. _ .....

TiOi

(mg)

0.01

.008

ZrOj 

(mg)

0.01

.006

FeiOi

(mg)

0.008

.005

No.

3.........................

4.........................

TiOi 

(mg)

0.02

.008

ZrOj 

(mg)

0.005

.01

Fe^j

(mg)

0.006

.005
148 METHODS OF ANALYSIS, URANIUM AND THORIUM

5. Optimum conditions lor th.e precipitation of tHorlum with, p-dlmethylamlnoazopnenylarsonlc acid

Effect of acid concentration: To each of six beakers were added a 

solution of thorium nitrate equivalent to 0.4 mg Th02 , 0.2 ml of hydrochloric acid, 1 g of ammonium acetate, and distilled water to make 

the volume to 43 ml. Ammonia was next added until the solutions 

were alkaline to methyl red. Dilute (7 + 100) hydrochloric acid was 

then added dropwise until the solutions were just acid to methyl red, 

followed by a known excess of dilute hydrochloric acid (7 + 100). 

Five milliliters of a saturated solution of ^-dimethylaminoazophenylarsonic acid in alcohol was added to each to precipitate the thorium. After digestion on the steam bath for 15 minutes, the 

thorium precipitates were filtered on Gooch crucibles and washed 

4 times with 10-ml portions of ammonium acetate wash solution. 

The precipitates were dissolved off the Gooch crucibles with 30 ml of 

4 percent sodium hydroxide arid the filtrates made to 250 ml. The 

solutions were then read in the electrophotometer. The readings 

obtained are listed below.

No.

1. ..... ..............

2.. . ....................

3.......................

Excess of 

7 percent 

HC1 added 

(milligrams)

0.1

.7

Optical 

density

0.21

.38

.54

 No.

4_. _.......,...._.._,...

5.. ...-.....-.-. 

e;..... ....... ..........

Excess of 

7 percent 

HC1 added 

(milligrams)

1.2.

3

6

Optical 

. density

0.55

.57

.90

1 Solution just acid to methyl red. . . .

The results obtained show that the acidity must be controlled. 

The optimum acidity taken is that given by a solution containing 

1 g of ammonium acetate and l!2'ml: of (7+100) hydrochloric acid in 

a total volume of 50 ml. .

Effect of concentration of ^-dimethylamuioazophenylarsonic acid: 

Using the Optimum acidity, the amount of p-dimethylaminoazophenylarsonic acid was varied in tWO tests. Using 2.5 ml Of the 

arSOniC add reagent, the optical density obtained was 0.525; using

10 mi of the arsonic acid reagent, the optical density was 0.575.

The concentration Of p-dimethylammoazophenylarsonic acid used

in the precipitation of thorium is evidently not important. The

Sffiall discrepancy noted above is probably due to the fact that the

precipitate was washed only four times in each experiment, so that

washing was probably not complete for the more concentrated solution. No attempt is made to wash all excess dye from the precipitate. Four washings are enough for practical purposes when 5 mi of

reagent is used.
PHOSPHATE-FLUORIDE-IODATE METHOD FOR THORIUM 149 

6. Interference of oxidizing agents In tne pnotometrle determination of thorium

Various amounts of thorium were precipitated as the iodate as in 

the procedure (step 19). The precipitates were filtered 24 hours later, 

dissolved off the filter with 25 ml of (1 + 1) hydrochloric acid and the 

paper washed with water. The solutions were evaporated to dryness, 

taken up with 4 drops of hydrochloric acid and 42 ml of water. The 

photometric procedure was then applied for the estimation of thorium. 

The results obtained are given'below.

ThOa 

taken 

(mg)

0. 15

.40

.75

1.4

ThOs/ound 

photometrically 

 (mg)

10. 135

.37

; . 67

1. 23

Percent 

recovery 

o/ThO,

90

92

90

88

The above experiments were repeated except that, after the hydrochloric acid solution of the iodate was evaporated to dryness, 8 ml 

of 6 percent sulfurous acid was added and the solution again evaporated to dryness. The residue was taken up with 4 drops of hydrochloric acid and 42 ml of water and the thorium estimated photometrically. The results given below show excellent recoveries.

ThOj ThOa found

taken photometrically

(mg) (mg)

0. 15 0. 155

. 40 . 395

.80 .80

1. 40 1. 41

7. Spectral transmlttancy and standard curves for the photometric determination of thorium with p-dlmethylamlnoazophenylarsonlc acid

The spectral transmittancy curve for the p-dimethylaminoazophenylarsonic acid solution obtained in the thorium determination is 

given in figure 21. The data were obtained with the Coleman Universal spectrophotometer Model II against water as reference, the 

concentration of thorium used being 0.1 mg Th02 per 100 ml. The 

standard curve, figure 22, was obtained with a Fisher electrophotometer, using a 425-millimicron filter. The solutions were prepared 

according to the procedure outlined in steps 24-27, page 142.

8. Inhomogenelty of the reagent p-dlmethylamlnoazophenylarsonlo acid

Two saturated alcoholic solutions of the reagent were made in this 

way: 1. Excess of y-dimethylaminoazophenylarsonic acid was digested with alcohol to make a saturated solution. Excess reagent 

was filtered from the solution which was labeled no. 1.
TRANSMITTA

 g
OPTICAL D
152 METHODS OF ANALYSIS, URANIUM AND THORIUM

2. The excess reagent obtained in the paper from (1) was treated 

with more alcohol to form a second saturated solution. This was 

filtered and labeled no. 2.

Various amounts of thorium were determined photometrically using 

the optimum conditions of excess acid and ammonium acetate, using 

alcoholic solutions nos. 1 and 2 for precipitation. The electrophotometer readings obtamed are given below:

ThOiiafcen Optical density 

(mg) Solution 1 Solution K

0. 15 0. 17 0. 21

.30 .34 .42

.45 .50 .58

.60 .64 .73

Both solutions follow Beer's Law up to about 0.4 mg Th02 , but they 

do not give the same density for the same amount of thorium.

In another experiment, 2 g of ^-dimethylaminoazophenylarsonic 

acid was ground to an impalpable powder in an agate mortar. Three 

0.1-g portions were weighed and to each were added 10 g of ammonium 

acetate, 25 ml water, and 25 ml of alcohol; they were warmed until 

solutions were obtained. This made three identical dye solutions. 

The results obtained when 0.4 mg ThO2 was determined photometrically by each solution are given below.

ThOj 

taken 

(mg)

0.4

. 4

.4

Optical 

density 

reading

0.60

. 60

.60

Reagent 

solution used 

(5 ml of each)

no. 1

no. 2

no. 3

Consistent results will therefore be obtained if a complete solution 

of thoroughly mixed reagent is used.

LITERATURE CITED

Fresenius, R., and Hintz, E., 1896, Uber die Untersuchung der Thornitrate des

Mandels und die Xremmung Von Xnorerde und Ceroxyd; Zeitschr. anal.

Chemie, v. 35, p. 525.

Hayes, W. G., and Jonee," E.' W'., 1941, Determination of zirconium in steel:

Indus. Eng. Chem., Anal. Ed. v. 13, p. 603-604.

Hillebrand, W. F., and Lundell, G. E. F., 1929, Applied inorganic analysis, p. 

416-425, New York, John Wiley and Sons.

Meyer, R. J., 1911, Der Nachweis und die Bestimmung des Thoriums mit Jodea.ure: Zei-fcsoVir. an.org. OKemie, v. 71, p>. 65.

Nazarenko, V. A., 1937, M6thode colorime'trique determiner le zirconium; Jour.

Applied chem. U. S. S. R. v. 10, p. 1696.

Pierson, G. G., 1934, Reducing"action of mercurous chloride: Indus. Eng. Chem., 

Anal. Ed. v. 6, p. 437-439.

Wyrouboff, G., and Verneuil, A., 1898, Sur la separation du thorium et des terres

de la cerite: Acad. sci. Paris Comptes rendus v. 126, p. 340.
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 19. THE GEOLOGICAL SURVEY CARBONATE-IODATEIODINE METHOD FOR THE DETERMINATION OF SMALL 

AMOUNTS OF THORIUM IN NATURALLY OCCURRING 

MATERIALS

By J. J. FAHEY and M. D. FOSTER

CONTENTS

Page 

Abstract..._ ___.______-___-________.__..-_-_-___-__.-_---_-____--. 154

Introduction.._...__._.._.._._._._.____.._._.____.._.__..._..__._. 154

Outline of procedure and discus8ion__--_______________.-___--_--_--_- 155

Procedure-______-_--______.--___--_____-_-_-_-___-.------_--_-_-_ 157

Decomposition of sample.__---_--_---_-__-.____-__-.-__-_-_____ 157

Extraction of iron..___________________________________________ 158

Separation of thorium._________________________________________ 158

Determination of thorium._____________________________________ 160

Colorimetric _.______________-._.___-_._______----_.__._.__ 160

Gravimetric _ __._________-.__._--__-_______-_--_--____--_ 161

Experiments _________________________________-.._..___..--______.._...._ 162

1. Analysis of synthetic mixtures.._______._.___._._-_-________-_ 162

2. Purity of ThOj obtained by the procedure..____.__--_-_____.__ 162 

, 3. Spectral transmittancy and transmittance-concentration curves of

carbon tetrachloride solution of iodine_________-_-._______--. 163

4. Synthetic color standards for the colorimetric determination of

thorium_ _ _________-.________________-____-------------- 166

ILLUSTRATIONS

FIGURE 23. Spectral transmittancy curve of iodine in carbon tetrachloride. 164

24. Transmittance-concentration curve for iodine in carbon tetrachloride -________-_____________-__-___-------_------- 165

25. Spectral transmittance curves of iodine in carbon tetrachloride,

methyl red in acid solution, thymol blue in acid solution._ 167

TABLES

r TABLE 1. Determination of thorium in synthetic mixtures of known

thorium content-______---_-___--_-_______---_--_------- 162

2. Spectrographic analyses of thorium oxide from gravimetric

determination._....._..____________..___.____________-_ 163

NOTE. This report was Issued as Trace Elements Inv. Kept. 31D, 1946.

268681 54 11 153
154 METHODS OF ANALYSIS, URANIUM AND THORIUM

ABSTRACT

A procedure is presented for the separation and determination of small amounts 

of thorium in naturally occurring materials. Thorium is separated from the rare 

earths and titanium by precipitating thorium iodate in the presence of peroxide. 

It is separated from zirconium by precipitating zirconium phosphate in acid 

solution. The thorium is finally collected as the iodate and determined either 

colorimetrically or gravimetrically depending on the amount. In the colorimetric 

procedure, the thorium iodate is treated with hypophosphorous acid which liberates iodine. The iodine is dissolved in carbon tetrachloride and the density of 

the solution measured photometrically. In the gravimetric procedure, the 

thorium iodate is dissolved in hydrochloric acid and ammonium hydroxide added 

to precipitate thorium hydroxide which is ignited to thorium oxide and weighed.

INTRODUCTION

During the course of Trace Elements investigations of the U. S. 

Geological Survey a method was sought for the accurate determination of small amounts of thorium in naturally occurring materials of 

widely different types. In the development of such a method, adequate 

provision had to be made for (1) the presence of phosphate, a major 

constituent of many of the samples; (2) the separation of thorium 

from interfering elements, such as titanium, zirconium, and the rare 

earths; and (3) the measurement of quantities of thorium of less than 

1 milligram.

The method should be applicable to most types of naturally occurring materials, with a minimum of modifications necessary to handle 

special types. Many of the methods described hi the literature are 

not applicable in the presence of phosphate, a major constituent of 

many of the samples, and these methods were therefore eliminated 

from consideration. Other methods, applicable in the presence of

phosphate, were designed for the determination of relatively large

amounts of thorium. Tests showed that these methods, under the

conditions usually recommended, were not sufficiently sensitive for the

determination of thorium in very small amounts.

For example, preliminary tests showed that when the quantity 

of thorium present is very small, complete recovery of thorium is not 

obtained in the strong nitric acid solution usually used in the iodate 

method. 1 As the iodate precipitation is applicable in the presence 

of phosphate and affords a separation of thorium from many other 

elements, experimental work was undertaken to determine whether 

or not complete precipitation could be obtained under different

conditions of acidity. This -work showed that complete recovery

can be obtained if the nitric acid content is less than 5 percent, but

a loss of thorium results if the acidity is as high as 10 percent. In 

the procedure presented in this report precipitation of thorium as

« Meyer, R. J., 1911, Der Nachwels und die Bestlmmung des Thoriums mit Jodsaure: Zeltschr. anorg 

Ohemie, v. 71, p. 65.
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 155

iodate in 3 percent nitric acid solution is combined with other wellknown reactions for the separation and determination of thorium. 

The method is especially designed for the determination of very small 

quantities of thorium (as low as 0.10 mg) in rocks and ores of widely 

different composition, but it can also foe ,usedjfor the determination 

of larger quantities of thorium. '^{IffjPS^P

OUTLINE OF PROCEDURE AND DISCUSSION

The essential features of the method are:

1. Complete decomposition of the sample.

2. Removal of essentially all iron (and molybdenum) by extraction with 

ethyl acetate from a (1 + 1) HC1 solution.

3. Precipitation of thorium with sodium carbonate. Any calcium, 

magnesium, titanium, zirconium, chromium, manganese, most of 

the rare earths, and some of the aluminum and phosphate are also 

precipitated.

4. Solution of the carbonate precipitate in HNOs and precipitation of 

thorium, zirconium, and titanium as iodates from 3 percent HNOa 

solution in the presence of hydrogen peroxide.

5. Digestion of the iodate precipitate with HNOa in the presence of 

excess phosphate, separating zirconium and part of the titanium 

from thorium.

6. Double precipitation of thorium as iodate in the presence of hydrogen 

peroxide, separating the rest of the titanium.

7. Determination of thorium spectrophotometrically by measuring the 

iodine equivalent of thorium iodate, or gravimetrically, as Th02, 

after reduction of thorium iodate and precipitation with NH4OH.

The sample is decomposed by the procedure given in part 2. 

Complete decomposition of the sample is essential as it should not be 

assumed that no thorium is present in undecomposed material. Any 

hydrolytic precipitates of tantalum, niobium, tin, titanium, zirconium, 

and tungsten, particularly in the presence of phosphate, may occlude 

thorium, and should be left in the solution. For samples having high 

contents of rare earths, it is advisable to add at this point the precipitate obtained in the final sodium hydroxide-peroxide step of the 

analysis for uranium on the same sample, part 4.

Iron, if present in large amounts, would precipitate with thorium 

in the iodate precipitation (Procedure, step 4), and remain with 

thorium in the acid treatment of the phosphates. Iron is therefore 

removed at the beginning of the analyses by extraction with ethyl 

acetate. This affords a quick and essentially complete separation 

and also reduces the bulk of the subsequent carbonate precipitate.

Thorium is precipitated, together with calcium, magnesium, titanium, zirconium, chromium, manganese, most of the rare earths, and 

some of the aluminum and phosphate, by the sodium carbonate 

precipitation. Uranium, which is in the filtrate, is separated from 

thorium, making it possible to determine both elements in a single 

sample.
156 METHODS OF ANALYSIS, URANIUM AND THORIUM

Precipitation as iodate in 3 percent nitric acid solution effects a 

preliminary separation of thorium, titanium, and zirconium from the 

other elements coprecipitated or occluded with them in the carbonate 

precipitation. If quadrivalent cerium is present, this is also precipitated as the iodate. However, part of the cerium and titanium is 

removed at this stage if the iodate precipitation is made in the 

presence of hydrogen peroxide. Any phosphate in the sample may be 

retained combined with titanium and zirconium. Hydrolyzed 

niobium and tantalum may also be retained.

Boiling and digestion of the precipitated iodates in strong nitric 

acid solution in the presence of excess phosphate result in a separation 

of zirconium and part of the titanium from thorium. Thorium phosphate, even in the presence of excess phosphate, is readily soluble in 

15 percent nitric acid solution. Zirconium phosphate is very insoluble, even at a much higher acidity. Tests showed that when 

zirconium phosphate is boiled in (1 + 1) nitric acid, and in concentrated nitric acid, the amount of zirconium dissolved is insufficient 

to give a precipitate with potassium iodate in 3 percent nitric acid 

solution. Titanium phosphate is much less soluble than thorium 

phosphate but is not as insoluble as zirconium phosphate. Any 

niobium and tantalum carried along to this point are removed with 

the insoluble zirconium phosphate. Cerium is soluble and remains 

in solution with the thorium.

The low acidity (3 percent) used in the final iodate precipitations 

of thorium requires a great reduction in the acidity of the filtrate 

from the acid treatment of the phosphates. This reduction of acidity 

is accomplished by precipitating the thorium, and any titanium and 

cerium present in this filtrate, with sodium hydroxide and dissolving 

the precipitate in (1 + 1) nitric acid. The volume of (1 + 1) nitric 

acid in which the hydroxide precipitate is dissolved plus the volume 

of wash solution used is adjusted to provide a final volume of 100 ml 

containing 3 percent by volume as nitric acid, after addition of hydrogen peroxide and potassium iodate solution in the subsequent

iodate precipitation.

Precipitation of thorium as iodate in the presence of excess hydrogen peroxide separates thorium from any titanium and cerium carried 

through to this point. A second iodate precipitation, again in the

f*vGseno© of e^ccess liycLrogjen. J>or-O3ca<io7 is desiz-o/ol© to roixio"vo <xn.y ro 

maining traces of titanium and cerium. Additional precipitations

with iodate are made if qualitative tests indicate that titanium or

cerium is still present. Usually two precipitations are sufficient, but 

additional precipitations may t>e necessary for samples j SUCfl &S

monazite, containing much cerium.
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 157

The presence of cerium in the solution is indicated at the time of 

the iodate precipitation by the development of an orange color accompanied by evolution of oxygen a few minutes after the addition 

of hydrogen peroxide and potassium iodate. Cerium catalyzes the 

reduction of iodate by peroxide in acid solution. After about half 

an hour the color gradually fades and evolution of oxygen ceases. 

The depth of color developed and the degree of evolution of oxygen 

is dependent on the amount of cerium present.

In washing the thorium iodate precipitate before the colorimetric 

determination, use a solution that wih1 completely remove potassium 

iodate from the filter paper and one hi which thorium iodate is insoluble. A number of wash solutions were tested, but none fulfilled 

the conditions as effectively as 76 percent alcohol. The size of filter 

paper recommended and the procedure for washing as outlined have 

been most satisfactory. It is suggested that the procedure be followed carefully.

When thorium iodate is reduced with hypophosphorous acid in 

the presence of sulfuric acid, iodine is quantitatively liberated. When 

the reaction takes place hi the presence of carbon tetrachloride, the 

iodine liberated is immediately dissolved, imparting a bluish-red 

color to the carbon tetrachloride. As the iodine liberated is directly 

equivalent to the thorium iodate reduced, the intensity of the color 

of the iodine carbon tetrachloride solution may be used as in indirect 

measurement of the thorium iodate. Because the measurement is 

indirect, it is essential that the thorium iodate be free of any other 

iodate.

In the gravimetric determination, it was shown by repeated determinations on samples of known thorium content that complete solution of the thorium and reduction of the iodate in the thorium iodate 

precipitate were brought about by treatment with concentrated hydrochloric acid. The thorium hydroxide precipitate must not be 

washed after filtration, as a small quantity of the thorium hydroxide 

will be carried through the paper. Weak ammonia and solutions of 

ammonium nitrate of different strengths tried as wash solutions were 

ineffective in preventing this. However, the amount of potassium 

chloride (the only contaminant at this stage) remaining in the welldrained precipitate and paper is of the order of 0.1 mg and most, if 

not all, of this is volatilized by the blast lamp.

PROCEDURE

DECOMPOSITION OF SAMPLE

1. Weigh out 5 g of the sample, if it has a total radioactivity 

equivalent to 0.015 percent U or less. Use proportionately smaller 

weights of samples having higher radioactivities. Prepare a hydro-
158 METHODS OF ANALYSIS, URANIUM AND THORIUM

chloric acid solution of the sample as outlined in part 2. Leave any 

hydrolytic precipitate obtained during the decomposition in the solution.

EXTRACTION OF IRON

2. After obtaining a (1 + 1) HC1 solution of the sample, evaporate 

the volume to about 25 ml. Transfer the solution to a 250-ml separatory funnel and shake with 40 ml of ethyl acetate. After the two 

layers have separated, draw off the acid layer into another separatory 

funnel of the same size. Add 20 ml of ethyl acetate, shake well, and 

after the layers have separated, draw off the acid layer into a 400-ml 

beaker. Combine the ethyl acetate layers and wash once by shaking 

with 5 ml of (1 + 1) HC1. Add the washing to the acid layer in the 

400-ml beaker.

SEPARATION OP THORIUM

3. Dilute the acid solution from the extraction of iron to a volume 

of 250 to 300 ml and heat to boiling. Remove the beaker from the 

heat and slowly add 50 percent NaOH solution until a slight permanent precipitate forms, add dry Na2C03 very carefully until 

effervescence no longer takes place, add 2 to 3 g of Na2C03 in excess 

and stir until all the Na2C03 is dissolved. Place the beaker in a cold 

water bath for % to 1 hour before filtering on a no. 40 Whatman 

12.5-cm paper. Wash the precipitate five times with a 1 percent 

Na2C03 solution.

If uranium is to be determined in the same sample, transfer the 

precipitate without washing to the original beaker with a fine stream 

of distilled water and add 7 ml of HCl. Dilute the solution to 250

or 300 ml, heat to boiling and reprecipitate as before with 50 percent 

NaOH and dry Na2CO3 . Cool and filter. Scrub out the beaker and 

wash the precipitate on the paper five times with a 1 percent Na2C03 

solution, Combine tne filtrates from the two carbonate precipitations for tlx© determination of uranium.

4. Transfer the carbonate precipitate to the original beaker with

a fine stream of distilled water. Add HN03 dropwise, with constant 

stirring, until the mixture is just red to methyl red, taking care to

disperse lumps of tne precipitate with, a stirring rod.. .Add 5.O ml of

HNOa in excess and make the volume up to 100 to 125 ml with distilled water, Add 50 ml of a 7 percent water solution, of KIO3 and

10 ml H202 (27 to 30 percent), stir, and let stand covered overnight.

Filter on a no. 42 Wnatman 9-cmj paper. Do nofcj wasli. Transfer the precipitate from the paper to tne original beaker Wltn a nH6

stream of distilled water. Replace the filter paper in the funnel

and pass 30 ml of (2 + 1) HNO3 through the paper into the beaker. 

By means of a stirring rod and by tipping, bring the solution into
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 159

contact with any precipitate left on the walls of the beaker. Adjust 

the volume to about 100 ml with distilled water.

5. Boil the solution plus any undissolved material for about 1 

minute, add 0.4 g of anhydrous disodium acid phosphate (Na2HP04), 

stir the solution well and digest (uncovered) on a steam bath until 

the volume is reduced to about 50 ml.

6. Filter on a no. 41 Whatman 9-cm paper, transferring most of 

the precipitate to the paper. If the filtrate is not clear, refilter on 

the same paper until a clear filtrate is obtained. Rinse out the 

beaker and wash the precipitate and paper with 40 ml of (1+9) 

HN03 containing 0.4 percent Na2HP04 (anhydrous).

7. Neutralize the filtrate to the methyl red end point with 50 percent NaOH solution and add 10 ml in excess. Digest on the steam 

bath for about 30 minutes. Filter on a no. 40 Whatman 9-cm paper 

(or a smaller no. 40 Whatman paper if the bulk of the precipitate 

permits). If the filtrate comes through turbid, refilter on the same 

paper until a clear filtrate is obtained. Do not wash the precipitate.

8. Place the filter paper containing the precipitate in the original 

beaker, add 6 ml of (1 + 1) HN03 and macerate the paper with the 

aid of a stirring rod. Add 25 ml of H20 and stir well.

Filter on a no. 40 Whatman 7-cm paper. Wash with 40 ml of 

distilled water, catching the filtrate and washings in a 150-ml beaker, 

and allow the paper to dram well.

9. To the combined filtrate and washings, the volume of which is 

now 70 ml, add 10 ml of H202 (27 to 30 percent) and 20 ml of a 7 percent water solution of KI03 . Stir and let stand overnight. The 

next morning add 5 ml of H2 02 (27 to 30 percent), stir and allow to 

settle about 1 hour.

Decant the supernatant liquid through a no. 42 Whatman 5.5-cm 

paper (or a 7-cm paper if the bulk of the precipitate is too large for a 

5.5-cm paper). Do not replace the stirring rod in the beaker during 

the decantation as this tends to stir up the precipitate. When about 

four-fifths of the supernatant liquid has been passed through the 

paper, replace the original receiver with a 50-ml beaker. Resume 

filtration. After most of the precipitate and all the liquid have been 

transferred to the paper, examine the filtrate in both the original and 

the second receiver. If it is not crystal clear, refilter on the same 

paper until a clear filtrate is obtained. Do not wash the precipitate. 

Test the filtrate for cerium by making ammoniacal in the presence of 

H202 . Place the paper containing the precipitate in the precipitation beaker, add 6 ml of (1 + 1) HN03 , and macerate the paper with 

the aid of the stirring rod. After an hour, add 25 ml of distilled 

water and stir well.
160 METHODS OF ANALYSIS, URANIUM AND THORIUM

Filter on a no. 42 Whatman 5.5-cm paper, catching the filtrate hi a 

150-ml beaker. If the filtrate is not clear refilter on the same paper 

until a clear filtrate is obtained. Wash the paper with 40 ml of distilled water and drain well.

10. To the filtrate and washings, the volume of which is now 70 ml, 

add 10 ml of H202 (27 to 30 percent) and 20 ml of 7 percent KIO3 

solution. Stir. If titanium and cerium are absent, follow step 12 

below. If the color of the solution indicates the presence of titanium 

or cerium, or if the filtrate from the previous iodate precipitate contained cerium (reddish-brown precipitate with ammoniacal H202), 

follow step 11.

11. Let the iodate precipitate stand overnight and follow the 

procedure of step 9. Repeat until cerium is removed. To the final 

filtrate and washings, the volume of which is 70 ml, add 10 ml of 

H202 (27 to 30 percent) and 20 ml of 7 percent KI03 solution. Stir.

12. Prepare a comparison solution containing 0.8 mg of Th02 in 

67 ml of water. Add, in order, 3 ml of HNO3 , 10 ml of H2O2 (27 to 

30 percent), and 20 ml of 7 percent KI03 solution. Compare the turbidity developed in the sample solution with that developed in the comparison solution. If, from the turbidity, the estimated content of the 

sample solution is less than 0.8 mg of ThO2 , determine thorium 

colorimetrically (steps 13-15); if the estimated content is more than 

0.8 mg of Th02 , determine thorium gravimetrically (step 16).

DETERMINATION OP THORIUM 

COLORIMETRIC

13. Let the thorium iodate precipitate stand overnight, add 5 ml 

of H202 (27 to 30 percent), stir and allow to settle. In about an 

hour, decant the supernatant liquid on a 42 Whatman 4.0-cm paper. 

Do not replace the stirring rod in the beaker during the filtration, 

as this tends to stir up the precipitate. When about four-fifths of 

the supernatant liquid has been passed through the paper, replace

the original receiver with a 50-ml beaker. Resume filtration. After

most of the precipitate and the last drop of the liquid have been transferred to the paper, examine the filtrate both in the original and

second receivers. If it is not crystal clear, refilter on the same paper

until a clear filtrate is obtained. Replace the receiver with a 30-ml

beaker. Rinse the walls of the precipitation beaker with a fine jet

of 76 percent alcohol (80 ml of 95 percent alcohol diluted with distilled water to 100 ml), Transfer the rinsings to the filter paper. 

Scrub the beaker with a policeman, again rinse the beaker with a 

fine jet Of 76 percent alCOhOl and transfer the rinsings to the paper as

before. Make a final rinse of the beaker with the alcohol solution 

and when this rinsing has drained through the paper, make 3 dis-
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 161

placement washings of the paper with the alcohol solution. When 

the last of the alcohol solution has drained through the paper shake 

the liquid from the stem of the funnel. Total alcohol washings of 

beaker and paper should not exceed 15 ml. Wash off the tip of the 

funnel with the alcohol solution.

14. Replace the receiving beaker with a 100-mm spectrophotometer cell. Treat the iodate precipitate on the paper in the funnel 

with 1 ml of (1 + 1) H2S04 , dropping it around the top, then tilt the 

funnel to bring the H2S04 in contact with any of the precipitate that 

may have crept above the top of the paper. Let the H2S04 remain 

in contact with the paper for about 5 minutes to permit complete 

solution of the precipitate. Wash the paper six times by running a 

fine jet of distilled water around the top of the paper. Total water 

washings should not exceed 10 ml.

15. Add 10 ml of carbon tetrachloride to the solution in the cell 

and 0.2 oil of hypophosphorous acid, stopper the cell and shake it 

for 2 minutes. Immediately place the cell in the cell receiver of the 

spectrophotometer and measure the optical density of the colored 

solution at 520 millimicrons wavelength. Obtain the milligrams 

Th02 equivalent by reference to a standard curve (Experiments, 3). 

If a spectrophotometer is not available, the ThO2 equivalent of the 

colored tetrachloride solution may be estimated by comparison with a 

series of standards prepared by mixing methyl red and thymol blue 

in acid solution to obtain a proper color tint (Experiments, 4).

GKAVEMBTBIC

16. After letting the thorium iodate precipitate (step 11) stand 

overnight, add 5 ml of 27 to 30 percent H202 , stir and allow to settle 

for about an hour. Filter on a no. 42 Whatman 5.5-cm paper (or a 

larger paper if necessary). If the filtrate is not crystal clear, refilter 

on the same paper until a clear filtrate is obtained. Make no effort to 

transfer all the precipitate to the paper. Do not wash. Allow the 

paper to drain well and place paper and precipitate in the precipitating 

beaker. Add 5 ml of HC1 and macerate the paper with the aid of 

the stirring rod. Place the beaker on the steam bath for about 5 

minutes, then add 75 ml of distilled water. While stirring, add 

NH4OH to the methyl red end point plus an additional 2 ml excess. 

Digest on the steam bath for about 15 minutes.

Filter on a no. 42 Whatman 5.5-cm paper, transferring all the 

precipitate to the paper by rinsing the beaker with a few milliliters 

of the filtrate. Do not wash. Allow the filter paper to drain well. 

Dry the precipitate, wrapped in its moist paper, in a weighed platinum 

crucible, char the paper slowly without allowing it to ignite, and burn 

the carbon off with a gradually increased flame. Finally heat at the
162 METHODS OF ANALYSIS, URANIUM AND THORIUM

full heat of a Meker burner and blast for about 5 minutes. Weigh 

the residue as Th02 .

EXPERIMENTS

1. ANALYSIS OP SYNTHETIC MIXTURES

The procedure described above was tested by determining thorium 

in solutions whose thorium content was not known to the analyst. 

The test solutions were prepared by adding different amounts of a 

standard thorium nitrate solution (10 ml=0.5 mg Th02) to 50 ml of 

either of two synthetic mixtures. The standard thorium nitrate 

solution was made from reagent-grade thorium nitrate that was 

found spectrographically to contain less than 0.1 percent of any other 

metal. The solution was standardized by precipitating the thorium 

as iodate from a 10-ml aliquot, filtering, reducing with concentrated 

HC1, precipitating with ammonia, and finally weighing as Th02 . 

As a check on the standardization, the ThO2 in eight samples containing 0.20 ml to 1.60 ml inclusive of the Th(NO3) 4 solution was 

precipitated as iodate and the iodine equivalent determined spectrophotometrically. The readings were then compared with a standard 

curve (Experiments, 3). The two methods of standardization 

checked very closely.

The synthetic solutions, labeled solution P and solution S, contained 

10 percent HC1. Their compositions are given in part 18 (p. 145).

In preparing the test samples, 50 ml of solution S or of solution P 

was used for each test sample. Definite quantities, unknown to the 

analysts, of standard thorium nitrate solution were added to each 

test sample, and thorium was separated and determined by the procedure described above. The results obtained are given in table 1.

TABLE 1. Determination of thorium in synthetic mixtures of known

thorium content

Sample

no.

T4 --....

Tj_ ..

Ti......

T.

T« _. ..

Tt.......

Type of

test

sample

s 

r

8 

P 

p

s

ThOi added

<m8>

0.05

.30 

.40 

.70

.90 

.80

ThOj found

Colorlmetrlcally

(mg)

0.11 

.42

.42 

.66

.70 

.83

Gravimetrioolly

(mg)

............

Sample 

DO.

Yi......

YT-. .

Y4- --

Ti......

Y,_ .....

Type of 

test

sample

p

8

p 

p

p 

p

ThOs 

added

(mg)

1.2 

1.4 

1.6 

1.85 

2.4 4.7

ThOj found

Colorimetrically (mg)

Gravimetrically

(mg)

1.2 

1.3 

1.6 

1.5 

2.2

4.0

2. PURITY OF ThOj OBTAINED BY THB PROCEDURE

TllC UlOriUIfl IB. f°Ur Synthetic samples was eeparated by tKe procedure described above and determined gravimetrically as InUj.
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 163

After weighing, the Th02 precipitates were analyzed spectrographically to determine if they were free from impurities. The results, 

given in table 2, show that the impurities in none of the precipitates 

amounted to more than 0.5 percent of the weight of the precipitate.

TABLE 2. Spectrographic analyses of ThO^ from gravimetric determinations

Sample no.

I......... ........ ........ .

2....._.__. ... ............ .

3............-... ....

4... .......................

ThOj 

precipitate 

(8)

0. 0016 

.0022 

.0024 

.0024

Percent

CeOj

0.1 

.3 

.4 

.2

ZrOj

0.003 

.01 

.01 

.01

SnOj

0.01 

.003 

.02 

.01

TlOa

0.003 

.007 

.006 

.006

NasO

0 

0 

0 

0

CaO

0 

0 

0 

0

Spectrographic analyses were also made of the Th02 precipitates 

obtained from four samples that were so high in cerium that it was 

necessary to repeat the iodate precipitation six times to obtain a filtrate that gave no test for cerium with ammoniacal H2O2 . The 

spectrograph showed that none of the samples contained more than 

0.3 percent Ce02 , 0.2 percent Zr02 , and 0.2 percent La203 .

3. SPECTRAL TRANSMITTANCY AND TRANSMITTANCE-CONCENTRATION CURVES OF CARBON TETRACHLORIDE SOLUTION OF 

IODINE

The spectral transmittancy curve of a carbon tetrachloride solution of 

iodine, against carbon tetrachloride as reference, is shown in figure 23. 

The curve shows a minimum transmittancy at 520 millimicrons. 

The instrument used was a Coleman Model II, and the cell was 18 

mm in diameter.

The transmittance-concentration curve of carbon tetrachloride 

solutions equivalent to different amounts of thorium is given in 

figure 24. To obtain this curve a solution of KI03 was used of which 

each milliliter was equivalent to 0.2 mg of Th02 , calculated on the 

assumption that the formula for thorium iodate is Th(I03) 4 . Definite 

amounts of the KI03 solution were measured into spectrophotometric 

cells, the volumes made up to 9 ml, and 1 ml of (1 + 1) H2S04 and 10 

ml of carbon tetrachloride were added in the order given. The color 

was developed in one sample at a time by adding 0.2 ml of hypophosphorous acid, stoppering, and shaking the cell for 2 minutes. The 

reading in the spectrophotometer of the transmittance of the sample 

was made immediately and before the development of the color in 

the next sample.
TRANSMITTANCY, IN PERC
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 165

EXPLANATION 

From KIOi

From Th precipitated as 

Th(IOi)4

0 .10 .20 .30 .40 .50 .60 .70 .80 .90 1.0

MILLIGRAMS OF THORIUM OXIDE

FIGURE 24. Transmittance-concentration curve for iodine In carbon tetrachloride.

The completeness of recovery of thorium iodate when precipitated 

from a 3 percent HN03 solution with 20 ml of 7 percent KI03 solution 

was checked as follows: Definite amounts of the standard thorium 

nitrate solution were measured out and the thorium precipitated as 

iodate, filtered after standing overnight, dissolved, and the color 

developed and read as described in the colorimetric procedure (steps 

13-15). The readings plotted on the transmittance-concentration 

curve obtained with KI03 solutions (figure 24) .indicate that the 

recovery of thorium as iodate from a 3 percent HN03 solution is 

complete within the limits of experimental error. The close agreement between these results and those obtained on a solution of KI03 

indicate that thorium iodate, precipitated under the conditions given 

in this procedure, has the formula Th(I03)4.
166

4. SYNTHETIC COLOR STANDARDS FOR THE COLORIMETRIC 

DETERMINATION OF THORIUM

The spectral transmittance curves of methyl red and thymol blue 

in acid solution are similar to the spectral transmittance curve of 

iodine in carbon tetrachloride. They have minimum transmittances 

at 520 and 540 millimicrons, respectively, compared with 520 millimicrons for iodine in carbon tetrachloride. From the curves (fig. 25), 

it appears that methyl red in proper concentration should closely 

match the color of iodine in carbon tetrachloride, but for visual 

comparison the color is not blue enough and it is necessary to add 

some thymol blue (in acid solution) to match the color exactly.

The standards may be prepared by visually matching different 

concentrations of an acid methyl red-thymol blue solution with iodinecarbon tetrachloride solutions prepared from known amounts of a 

KIO3 standard solution, or, if a spectrophotometer is available, by 

adjusting such mixtures to give the proper readings on the spectrophotometer for iodine equivalent to definite amounts of thorium, 

Such synthetic standards have been found stable for about a month.
CARBONATE-IODATE-IODINE METHOD FOR THORIUM 167

100

300 400 500 600 700 800

WAVELENGTH IN

FIGURE 25. Spectral transmittancy curves of iodine in carbon tetrachloride, methyl red in acid solution,

thymol blue in acid solution.

BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 20. THE DETERMINATION OF THORIUM IN HIGHGRADE AND LOW-GRADE ORES

By F. S. GRIMALDI and CHARLOTTE MARSH WARSHAW

CONTENTS

Page 

Introduction.___-__-.__...____-_____._._______.________._.___.__._ 169

Outline of procedure and discussion__--____-,._________---___--_...__ 170

Solution of the sample_____.____._.._________..__..__.__._.____ 170

Major separations-_____-_-_,______.__.__-._______.-._____.._.. 170

Procedure ________________________________________________________ 172

Experiments.___--__--____-_-_-._.______.._.__________________..__ 175

Failure of the peroxynitrate precipitation of thorium in the presence 

of zirconium.________________________________________._____ 175

Separation of thorium from rare earths by the peroxynitrate method. _ 176

TABLES

TABLE 1. Comparison with results by the phosphate-iodate method.._.__ 174

2. Incomplete precipitation of thorium peroxynitrate in presence

of zirconium.____--_---____----___-___-_---____--_-.__-_ 176

3. Separation of thorium from rare earths by peroxynitrate method. 176

INTRODUCTION

A procedure is described for the determination of thorium in monazite ores that is applicable to other ores of a wide range of composition. It is successful for both high- and low-grade ores (to as little as 

0.04 percent thorium oxide).

Thorium is separated from calcium, magnesium, and from most of 

the rare earths by double precipitation with ammonia, then from 

such elements as zirconium, titanium, and niobium by precipitation 

as fluoride, and separated from the remaining rare earths by peroxynitrate precipitation.

Zirconium and sulfate interfere with the peroxynitrate precipitation. These interferences can be successfully overcome under certain 

conditions.

This new procedure is designed for ores containing 0.04 percent 

thorium oxide and more. It is reasonably rapid, enabling a chemist 

to start a sample one day and obtain the results the next day.

NOTE. This report was issued as Trace Elements Inv. Kept. 44 and AECD 2818,1947.

268681 54 12 169
170 METHODS OF ANALYSIS, URANIUM AND THORIUM

We thank C. J. Rodden of the National Bureau of Standards for 

the use of laboratory space and also for permission to quote Maczkowske's thorium analyses.

OUTLINE OF PKOCEDTJRE AND DISCUSSION

The essential features of the method are:

1. Decomposition of the sample by fusion with Na20z.

2. Solution in HNOi and precipitation with NaOH-H2 02 (separation from 

most of the phosphorus, aluminum, and silica).

3. Double precipitation with ammonia at the methyl red end point (separation from calcium, magnesium, manganese, and most of the rare 

earths).

4. Precipitation as fluoride (separation from zirconium, titanium, niobium, 

and iron).

5. Solution of the fluoride by fusion with KjSaO? and removal of sulfate 

by two NaOH-H^Oa precipitations.

6. Repetition of steps 3, 4, and 5.

7. Precipitation as peroxynitrate (separation from the remaining rare 

earths) and ignition to oxide.

SOLUTION OF THE SAMPLE

The sample taken for analysis should be 2 g or less. In general, 

an 0.5-g sample suffices. If a 2-g sample contains less than 0.5 mg 

ThO2 , the trace procedure given in part 18 is more suitable. 

P§The finely powdered sample is decomposed by fusion with sodium 

peroxide, and the melt leached with water. The hydroxide precipitates that form may go through the filter, if filtered off at this point. 

Acid is therefore added to dissolve the precipitate, and then a 

NaOH-H202 precipitation is made. This precipitation separates 

thorium from the silica, phosphorus, and aluminum. Magnesium 

and a large part of the calcium accompany thorium and are separated 

later.

MAJOR SEPARATIONS

1. Separation of thorium from rare earths, calcium, magnesium, 

and manganese, by ammonium hydroxide.

Thorium is separated from calcium, magnesium, manganese, and 

most of the rare earths by ammonium hydroxide precipitations at 

controlled acidity.

The precipitation of thorium with ammonia is quantitative at a

p~EL corresponding to tne neutral color of metnyl red, and at tnis

acidity trivalent cerium and the other rare earths remain largely in 

solution. Either nitrate or chloride solutions of thorium may be 

used, but sulfate must be absent. If sulfate is present, considerable 

losses of thorium result at the methyl red end point, although precipitation of thorium is complete when excess ammonia is used. It is
DETERMINATION OF THORIUM HIGH-GRADE, LOW-GRADE ORES 171

absolutely necessary, therefore, to remove sulfate before making 

ammonia precipitations at the neutral point of methyl red.

2. Separation of thorium from iron, aluminum, zirconium, titanium, 

and niobium, by hydrofluoric acid.

Thorium is separated from the members of the R203 and acidinsoluble groups with hydrofluoric acid. Hydrofluoric acid is faster 

and more reliable than oxalic acid for this separation especially when 

small amounts of thorium are involved. Hydrofluoric acid has the 

added advantage of dissolving any hydrolytic precipitate of the above 

elements. As an example, if titanium or niobium were to hydrolyze 

out of solution, oxalic acid solution would not dissolve the precipitate 

unless the precipitate were filtered off, fused with pyrosulfate, and 

the melt leached with oxalic acid. Hydrofluoric acid takes these 

hydrolytic precipitates directly into solution.

3. Separation of thorium from rare earths by peroxynitrate precipitation.

The small amounts of rare earths left with the thorium after 

ammonia precipitation are removed by precipitation of thorium 

peroxynitrate in 0.03N nitric acid. Fenner 1 says,

The precipitation of thorium with hydrogen peroxide is apparently sensitive 

to changes of conditions, and the method has been thought by some workers to 

be unreliable. There seems to be some basis for this view, as I have found that 

unless certain requirements are fulfilled, hydrogen peroxide will fail to precipitate 

some or even a large part of the thorium . . .

We agree with Fenner. The peroxynitrate precipitation is influenced by the acidity of the solution, by the concentration of hydrogen 

peroxide, by various anions and cations, as well as by the order of 

addition of reagents. For best separation from the rare earths, the 

acidity should be as high as possible, because at lower acidities cerium 

tends to be oxidized by the peroxide and to contaminate strongly the 

thorium. We believe that the highest acidity at which no thorium 

is lost is very close to a pYL of 1.5. Precipitation at this acidity is 

greatly influenced by the presence of zirconium. When zirconium is 

present, both thorium and zirconium tend to "lose their identity." 

Certain combinations of zirconium and thorium will actually fail to 

yield any peroxynitrate precipitate, but generally thorium and zirconium are incompletely precipitated. The losses for thorium are 

usually less than 1 mg (Experiment 1). The peroxynitrate precipitation, thus, cannot be used unless provision is made first to remove 

zirconium completely. The procedure given is designed to eliminate 

this element. The separation obtainable when zirconium is absent 

is shown under Experiments 2.

< Fenner, C. N., 1928, The analytical determination of uranium, thorium, and lead as a basis for agecalculation: Am. Jour. Sci., 5th ser., v. 16, p. 369-381.
172 METHODS OF ANALYSIS, URANIUM AND THORIUM

The effect of titanium on the peroxynitrate precipitation of thorium 

was not studied thoroughly, but it was noted in one experiment 

(5 mg ThO2 +10 mg TiO2) that this element did not behave like 

zirconium, as complete precipitation of thorium was obtained.

Sulfate also interferes in the peroxynitrate precipitation of thorium 

in 0.03N nitric acid causing low recoveries. The losses are about 2 

mg or less. Sulfate is eliminated by NaOH-H2O2 precipitation of 

thorium before the peroxynitrate step.

The amount of ammonium nitrate used does not seem to be an 

important factor in the peroxynitrate precipitation, but some should 

be present. The amount of hydrogen peroxide should be more than 

2 ml of 30 percent H202 per 100 ml of solution, because with higher 

concentrations of peroxide there are less interferences.

PROCEDURE

1. Fuse 0.5 g of finely powdered sample with about 3 g Na2O2 in a 

porcelain crucible.

2. Disintegrate the melt with 180 ml warm water. Neutralize 

with HN03 (1 + 1) and add a few milliliters in excess. Remove and 

rinse crucible, adding rinses to the solution. Cool the solution to 

about 50 C.

3. Add 1 ml of 30 percent H202 and precipitate with 50 percent 

NaOH solution adding 10 ml in excess. Digest on the steam bath a 

few minutes. Cool. Filter and wash thoroughly with warm 0.1 

percent NaNO3 .

4. Transfer the precipitate from the filter to the original beaker 

and dissolve what remains on the filter with 15 ml warm HNO3 (1 +1). 

Wash the paper with water. Reserve the paper. Boil the solution

gently for about 5 minutes to destroy most of the peroxide. Dilute

to 190 ml with water. Cool. Add NH4OH until a precipitate forms 

that clots, avoiding too great an excess of ammonia (one or two drops 

excess). Add 3 drops of 0.1 percent methyl red in alcohol and neutralize carefully with HN03 (1+50) until the methyl red color is just 

yellow or just under salmon pink. Heat the solution until it starts to 

boil, Remove the heat, and when the precipitate settles, check the

acidity as indicted by methyl red and adjust if necessary. Filter the 

solution and wash with 0.1 percent NH4NO3 .

5. Dissolve the precipitate off the filter with 15 ml of warm HN03 

(1 + 1) and wash the filter paper thoroughly with water. Reserve the 

paper. Repeat the ammonia precipitation as in step 4.

6. Unfold the paper and with a little water transfer the hydroxide 

precipitate to a platinum dish. Combine the filter paper with those 

reserved hi steps 4 and 5, ash them, and add the ash to the dish con-
DETERMINATION OF THORIUM HIGH-GRADE, LOW-GRADE ORES 173

taming the major precipitate. The volume of the solution at this 

point should be about 15-25 ml.

7. Add 10-15 ml of HF, cover the dish with a platinum cover, 

and digest the solution on the steam bath for at least 1 hour, stirring 

occasionally. Allow the sample to stand half an hour at room temperature.

8. Filter on no. 40 Whatman paper through a hard rubber funnel 

and wash once with dilute HF and twice with water. Transfer the 

precipitate to a platinum crucible, cover the crucible loosely with a 

platinum cover to allow access of air, and burn the precipitate carefully at low heat.

9. Add as little K2S207 as will dissolve all the precipitate (1 g or 

less depending on the size of the fluoride precipitate) and fuse carefully until a clear melt is obtained. Care should be taken during the 

fusion to prevent the loss of thorium by spattering. Cool. Leach the 

melt with 300 ml of water containing 10 ml HN03 (1 + 1).

10. Warm the solution to about 50 C. Add 0.5 ml 30 percent H202 

and precipitate with 50 percent NaOH solution, adding about 4 ml in 

excess. Digest the sample a few minutes on steam bath. Cool. 

Filter through a fast paper and wash the precipitate thoroughly with 

warm 0.1 percent NaN03 . This precipitation as well as the precipitation in step 11 is made to free the sample from sulfate.

11. Dissolve the precipitate off the paper with 10-15 ml of warm 

HN03 (1 + 1) and wash the paper with water. Reserve the filter 

paper. Reprecipitate with NaOH-H202 as in step 10. Filter and 

wash the precipitate with 0.1 percent NaN03 .

12. Dissolve the precipitate off the paper with 10-15 ml of warm 

nitric acid (1 + 1) and wash the paper with water. Reserve the filter 

paper. Bring the solution to a boil and simmer gently for about 5 

minutes to destroy the peroxide. Adjust the volume of solution to 

about 150 ml. Cool. Add NH4OH in very slight excess until a precipitate forms that clots. Add a few drops of methyl red and carefully 

neutralize to just yellow or just under the salmon pink color of methyl 

red. Heat the solution until it just starts to boil. Remove the heat 

and allow the precipitate to settle. Check the acidity and adjust if 

necessary. Filter through a fast paper and wash with 0.1 percent 

NH4N03 solution.

13. Dissolve the precipitate off the filter with 10-15 ml HN03 

(1 + 1) and wash the paper with water. Reserve the filter paper. 

Reprecipitate with NH4OH hi the same manner. Filter and wash 

with 0.1 percent NH4NO3 . Transfer the paper with precipitate to a 

platinum crucible and add the filter papers reserved in steps 11, 12, 

and 13. Ash at a low heat, keeping the crucible loosely covered.
174 METHODS OF ANALYSIS, URANIUM AND THORIUM

14. Fill the crucible two-thirds full with HF (about 10 ml) cover 

and digest on the steam bath % to 1 hour, depending on the size of the 

precipitate. Transfer to a platinum dish with a stream of water, 

scrubbing the crucible thoroughly. Adjust the volume of the solution 

to 25-30 ml with water. Allow to settle a few minutes and filter. 

Wash with dilute HF and then twice with water. Burn the precipitate 

carefully in a covered crucible.

15. Dissolve the fluoride precipitate with potassium pyrosulfate as 

before. Make two NaOH-H202 precipitations as before.

16. Dissolve the final NaOH-H202 precipitate with 10 ml of 

(1 + 1) HN03 . Boil the solution 5 minutes to destroy most of the 

peroxide and reduce the cerium. Cool. Add NH4OH in very slight 

excess until a precipitate forms. Add 2 drops of methyl red and 

neutralize with dilute HN03 until the color is just red. Add exactly 

1 ml of (1+4) HN03 and 5 ml of 30 percent H202 and stir. Adjust 

the volume of the solution to 95 ml by adding water and bring the 

solution to a boil. Digest the precipitate on the steam bath 5 minutes, 

add filter-paper pulp, filter, and wash thoroughly with NH4N03 wash 

solution. Burn the precipitate carefully in a loosely covered platinum 

crucible at low heat. Raise the temperature to about 850 C and 

ignite to constant weight. The peroxynitrate precipitate of thorium 

tends to spatter and may be lost mechanically if the heating is hurried 

and the crucible not covered.

Occasionally another peroxynitrate precipitation may be necessary. 

If the precipitate is off-color instead of white, the peroxynitrate is 

dissolved in 10 ml of hot (1 + 1) HN03 , the solution is boiled to 

remove peroxide and reduce cerium, and the thorium is reprecipitated

with H202 before igniting and weighing.

The samples were analyzed by the above procedure and also by the

phosphate-iodate procedure described in part 18. Table 1 gives the 

results obtained on 0.5-g samples,

TABLE 1. Comparison with results by the phosphate-iodate method

Sample no.

NBS2601.....................

NBS-OP 75-10................

NBS 2601, diluted............

Euxenite 

NBS-CF 75-4................

NBS-OP 75-6.... ...........

ThOz procedure in 

text (per9.60

4.16 

I'll 

1.01

.68 

.44

ThOj phosphate-iodate 

procedure

9.65

4.30

3.08

1.13

1.00

.66 

.41

Eemarks

This is a standard monazite sand. The

average result of five cooperating laboratories was 9.65 percent ThOz. 

Maczkowske at National Bureau of Standards reports 4.34. 4.20. 2v£on£»&ite sand.

Maczkowske at National Bureau of Standards reports 1.13.
DETERMINATION OF THORIUM HIGH-GRADE, LOW-GRADE ORES 175

EXPERIMENTS

FAILURE OF THE PEBOXYNITBATE PRECIPITATION OF THORIUM 

IN THE PRESENCE OF ZIRCONIUM

In these experiments the combination 5 mg of Th02 and 10 mg 

Zr02 (added as the nitrates) was used. Analyses of solutions containing this combination failed to give quantitative recoveries of 

thorium no matter what conditions or techniques were used. The 

losses generally amounted to about 2 mg of Th02 or less.

The procedure used except for test no. 1 was as follows: The 

thorium and zirconium nitrates were added to a 150-ml beaker. 

The solution was diluted to 90 ml with water. A prescribed amount 

of solid NH4N03 was added and dissolved. Dilute NH4OH was next 

added to the yellow color of methyl red. Dilute nitric acid was added 

until the color turned to just red. The solution was heated just to 

boiling and the source of heat was removed. A prescribed amount of 

30 percent H2O2 was added, the solution stirred once, and a prescribed amount of nitric acid was added immediately. The volume of 

the solution was made to 100 ml with water and the sample digested 

on the steam bath for a prescribed length of time. The precipitate 

was filtered and washed with ammonium nitrate solution. Quantitative analyses for thorium were made on some of the precipitates; 

in other tests, the filtrates were tested qualitatively for thorium.

In test no. 1 the solution of zirconium and thorium was made 

neutral to methyl red and a prescribed excess of dilute HNO3 was 

added. The peroxide was next added and the solution digested 

before filtering.

In test no. 20 the precipitation was made in a glass-stoppered 

Erlenmeyer flask and the solution heated on the steam bath under its 

own pressure 10 minutes before filtering off the peroxynitrate 

precipitate.

Table 2 shows that in no case was precipitation of thorium complete.
176 METHODS OF ANALYSIS, URANIUM AND THORIUM

TABLE 2. Incomplete precipitation of thorium peroxynitrate in presence of

zirconium

[6 mg ThOj+10 mg ZrO» used for each experiment. Total volume 100 ml]

Test no.

2............. 

3. 

4.. ......................................

5.. ................ .. . .._.- .....

6 __ ....... . 

7....... -.-...-.. .................... .

8........ .............. .... .. 

9.. 

10... . 

11...... --

12...... . 

13__ 

14... 

15....... 

16....... .... .

17. 

18.. 

19... . .

20.... . .

Amount 

NHiNOs 

(g)

7

2

10

20

7

7

7

7

7

5

20

7

7

7

7

7

20

20

20

7

Amount 

excess 

(1+4) 

HN03 

(ml)

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

.60

.50

.50

.50

.50

.50

.50

.50

.50

.50

1.00

Amount 

of 30 

percent 

HjO, 

(ml)

2

2

2

2

6

10

20

5

16

2

2

6

20

5

6

20

10

10

20

10

Time of 

digestion of 

peroxynitrate 

precipitate 

before 

filtration 

(minutes)

5

5

5

6

5

5

6

30

60

5

5

5

5

10

60

20

6

20

20

UO

ThOa 

recovered 

(mg)

3 Q

4 9

4.2

4.3

4.4

4.5 (')

0)

(0

0)

0)

4.J5

4.4

(')

4.6 (')

(')

(')

0)

1 Incomplete. 

1 Under pressure.

SEPARATION OF THORIUM FROM RARE EARTHS BY THE 

PEROXYNITRATE METHOD

Table 3 illustrates separations obtainable by peroxynitrate when 

zirconium is absent.

Cerium was added as cerous ammonium nitrate, thorium as nitrate, 

and the yttrium group as nitrates.

TABLE 3. Separation of thorium from rare earths by the peroxynitrate method

Taken

0.0564 g THOa+0.30 g CeOj.. ................................................

0.0564 g ThOj+0.20 g YjOj group.. .................................

0.2256 E ThOjH-0.006 g CeOi.... . -

0.0023 g ThOz+0.36 g CeOs.. ......... .......... .............................

0.0023 g Th024-O.QO g YS 03 group.. 

Number of peroxynitrate 

precipitations made

2

2

1

1

2

i

i

ThOa found 

(g)

0.0568

.0567

. 22SO

.2255 on?1}

.0026

.0023
BULLETIN 1006. COLLECTED PAPERS ON METHODS OF ANALYSIS 

FOR URANIUM AND THORIUM

Part 21. MESITYL OXIDE EXTRACTION METHOD FOR 

THORIUM ANALYSIS

By HARRY LEVINE and F. S. GRIMALDI

CONTENTS

Introduction. _____________________________________________________ 177

\ Extraction of thorium nitrate by some organic solvents.________________ 178

Extraction of thorium nitrate by mesityl oxide________-______-----,_-_ 179

Metal nitrates extracted by mesityl oxide--_______-_-_-_---_---_-_--_- 180

Effect of phosphate, arsenate, sulfate, and borate in the extraction of

thorium nitrate by mesityl oxide.-___-________--_._.___----_----_. 181

Analysis of thorium ores_____________.__..________-__-_-_-__---_-. 181

Outline and discussion.-.._________-_________-_..-_--_-__-_-_-. 181

Detailed procedure.__-______-_______________--______-____---_- 183

Results of analyses.---____-__._____._____._______-_._-__-___-_--_. 184

TABLES

TABLE 1. Extraction of thorium nitrate by an equal volume of various 

v organic solvents____-___-_________._________---_-----___ 179

2. Extraction of thorium nitrate by an equal volume mesityl oxide. 180

3. Extraction of different elements by an equal volume of mesityl

oxide ...-_--_-_--_-----_---_-------.-------------. 180

 * 4. Effect of phosphate in the extraction of thorium by mesityl

oxide_ _____-______-______.____._._-____-__-_--_---___ 181

5. Analysis of thorium ores.._____-_-_-______-___--__------___ 185

INTRODUCTION

Thorium nitrate is quantitatively extracted by mesityl oxide from 

solutions saturated with aluminum nitrate even in the presence of 

relatively large amounts of phosphate. Uranium is the only other 

element extracted quantitatively by a single extraction. Zirconium 

is extracted to a large extent, yttrium and vanadium to a small 

extent, and cerium in both valence states only to a very slight degree. 

Ceric cerium is reduced probably by the olefinic bond in the solvent. 

Mesityl oxide thus is useful not only for the concentration of uranium 

and thorium but also for the separation of thorium from the rare 

earths, the separation taking about 10 minutes per sample.

NOTE. This report was Issued as Trace Elements Inv. Kept. 105 and AEOD 3186,1950.

177
178 METHODS OF ANALYSIS, URANIUM AND THORIUM

The mesityl oxide procedure for the determination of thorium has 

been applied to a wide variety of thorium ores such as monazite, 

black sand, thorianite, thorite, euxenite, and eschynite.

Solvent extraction methods for the concentration and purification 

of thorium are important. Extraction from nitric acid solutions is 

of special interest in that not only thorium but also uranium may be 

concentrated. It has been known for some tune that thorium nitrate 

is soluble in organic solvents. The earliest papers on this subject 

were by Misciattelli 1 and Wells 2 and gave data on the solubility of 

thorium nitrate in ether. In a recent paper, Rothschild and others 3 

give data on the distribution of thorium nitrate to various ketones 

and alcohols.

As far as we know, practically no work has been done on the 

application of the thorium nitrate extraction process to the chemical 

analysis of thorium. This paper describes the use of a new solvent, 

mesityl oxide, together with aluminum nitrate as the salting agent, 

in the analysis of thorium ores.

EXTRACTION OF THORIUM NITRATE BY SOME 

ORGANIC SOLVENTS

Preliminary studies were made on some organic solvents to determine which ones were most efficient in extracting thorium nitrate. 

These data are included in this report because they may be significant,

In these experiments a standard solution of thorium nitrate (1 ml= 

0.0010 g Th02) was first made by dissolving the pure salt of known 

composition in nitric acid (15+85). To 5 ml of this solution 9.5 g 

of aluminum nitrate crystals were added and the mixture was warmed 

to dissolve the aluminum nitrate. The solution was then cooled to 

room temperature. This amount of aluminum nitrate was found to 

nearly saturate 5 ml of solution (15 percent by volume in nitric acid) 

at room temperature. When the aluminum nitrate is dissolved, the 

volume of the solution increases to about 10 ml or about double the 

original volume. The solution was then poured into a 60-ml separatory funnel. Ten milliliters of the organic solvent under test was 

pipetted into the beaker that contained the original solution and the 

solvent was agitated. The solvent was then poured into the separatory funnel containing the thorium solution to be extracted. The

separatory funnel was agitated vigorously for 15 seconds and the 

liquid layers were allowed to separate. The water layer was drawn

> MisciatteLIi, P., 1929, On the separation of thorium from uranium by means of ether: Phil. Mag., v. 7, 

p. 670.

» Wells, Roger C., 1930, The solubility of some rare-earth nitrates in ether: Washington Acad. Sci. Jour., 

v. 20, no. 8.

« Rothschild, B. P., Templeton, 0. C., Hall, N. P., 1948, The distribution of thorium nitrate between 

water and certain alcohols and ketones: Physical and Colloid Chemistry Jour., v. 52, no. 6.
MESITYL OXIDE EXTRACTION METHOD FOR THORIUM ANALYSIS 179

off and rejected. The solvent layer was then washed once with 10 

ml of aluminum nitrate wash solution (2.5M in aluminum nitrate and 

1.2N in HN03), the wash solution later being rejected. The washed 

solvent layer was withdrawn and evaporated to dryness. The residue 

obtained was gently ignited to remove carbon. The residue was then 

treated with hydrofluoric acid to remove aluminum and the thorium 

fluoride was collected, washed, and ignited. This was brought into 

solution by fusing with potassium pyrosulfate. The melt was cooled, 

a little dilute nitric acid was added, and the mixture was warmed to 

dissolve the cake. The thorium was precipitated with an excess of 

freshly distilled ammonium hydroxide and the thorium hydroxide 

ignited to thorium oxide and weighed as such.

Table 1 shows the results obtained with the organic solvents tested. 

This shows that butyl lactate, cyclopropyl methyl ketone, and 

mesityl oxide gave the best recoveries of thorium. Cyclopropyl 

methyl ketone is expensive, hard to obtain, and was not considered 

further. Both butyl lactate and mesityl oxide extracted about the 

same amount of zirconium. Butyl lactate, however, extracted much 

more aluminum nitrate than mesityl oxide did and for this reason 

was not studied further.

EXTRACTION OF THORIUM NITRATE BY MESITYL OXIDE

In these experiments thorium nitrate representing respectively 

0.4 ing, 1.0 nag, 5.0 mg, 15.0 mg, 50.0 mg, and 100.0 mg of thorium 

oxide were added to 10-ml portions of nitric acid (15+85). Nineteen 

grams of aluminum nitrate crystals were added and dissolved and the 

solutions obtained were each extracted once with 20 ml of mesityl 

oxide by shaking for 15 seconds. The mesityl oxide extract was then 

analyzed for thorium after eliminating any aluminum with hydrofluoric acid. The results given in table 2 show that quantitative 

recovery was obtained for all portions.

TABLE 1. Extraction of thorium nitrate by an equal volume of various organic

solvents

[Thorium solution 2.5 M in aluminum nitrate and 1.2 N in HNOs]

Solvent

Amyl acetate ___ . ________ . ...

0-Ethoxy ethyl acetate .................

Ethyl acetate _______ ... __ . .....

Ethyl butyrate... ____________

Thorium 

extracted 

(percent)

40

30

<1

<1

>99.9

<1

32

80

45

35

<1

Solvent

Methyl propionate.. ______

Amylene dichlorlde .....................

Anisole __________________

n-Butyl ether. ..........................

2,6 dimethyl furan _______ . ........

Ether ________ .. ___ ... ........

Cyclopropyl methyl ketone _____ ...

Methyl n-amyl ketone- .................

Methyl cyclohexanone ..................

Thorium 

extracted 

(percent)

45

<1

<1

35

<1

35

92

>99.9

90

96

>99.9
180 METHODS OF ANALYSIS, URANIUM AND THORIUM

TABLE 2. Extraction of thorium nitrate by an equal volume of mesityl oxide 

[Thorium solutions 2.5 M in aluminum nitrate and 1.2 N in HNOj]

ThOj

taken

(nig)

0.4

1.0

5.0

ThO.

extracted

(mg)

0.4

1.0

5.0

ThOi

taken

(mg)

15.0

50.0

100.0

ThOj

extracted

(mg)

15.1

50.0

100.1

METAL NITRATES EXTRACTED BY MESITYL OXIDE

In these experiments a salt (generally the nitrate) of the element 

under test was dissolved in 10 ml of HN03 (15+85). Nineteen 

grams of aluminum nitrate crystals were then added and dissolved. 

The solution obtained was then extracted once by shaking with a 

20-ml portion of mesityl oxide for 15 seconds. The mesityl oxide 

extract was washed once with 20 ml of aluminum nitrate wash solution and evaporated to dryness on the steam bath after the addition 

of a slight excess of NH4OH (it was necessary to add NH4OH to prevent 

violent bumping during the evaporation of mesityl oxide). The 

residue was ignited, dissolved, and tested quantitatively for the 

element under study. The results are shown in table 3.

TABLE 3. Extraction of different elements by an equal volume of mesityl oxide 

[Solution 2.5 M in Al(NO»)i and 1.2 N in HNOs]

Salt

Calcium nitrate... . 

Neodymium ammonium nitrate.

Cerous ammonium nitrate-. _.

Yttrium nitrate.......... 

Manganous nitrate... ........

Ammonium^etavanadate __

Uranyl nitrate. . 

Nickelous nitrate.. . 

T and nitfflro

Weight of element 

taken 

(grams)

0.1 

.1

.1 

.1

.05 

.05

.05

.05 

.025

.06

.05

 05 '.05

.0500

.05

.05

.05

. O25

.05

.05

.05 

.05

Amount extracted 

(grams)

None.. 

0.00008 BeO... .

0.074 Zr.. ...... 

None.... 

O.OOO8 CeOi- .---

None ______ .

0.0024 Y20j... 

0.0002 MnO 

0.008 VaOs... - -

O.OO004 Oo_ ______

0.0500 U... ........

0.0004 CuO........

None...... 

O.OOO4 SnO«- ___ _ _

None.............

0.002 In.. .........

0.004 Pt ... 

Method of test

Oxalate. 

Fluorimetric-quinizarin. 

NaOH precipitate. 

Evaporation of solvent and ignition of 

residue.

Do

No precipitate with HF.

-STaOH-ETaO.. 

NaOH-H^Os. No precipitate with HF. 

HF; NaOH-HsOj followed by NH<OH;

also spectrographic.

HaOo.

KI04 . 

H.O,.

^TBC.OIsrS-acotono 

ICONS.

Zinc reduction and KMnOi titration. Ammonia blue color.

SnoctroeraDhic. Dimethylglyoxime,

SnClr-KCNS.

Spectrographie. 

JSTo BaSO* precipitate.

No FbS precipitate.

Spectrographic. 

Reduction with formic acid.
MESITYL OXIDE EXTRACTION METHOD FOR THORIUM ANALYSIS 181

EFFECT OF PHOSPHATE, ARSENATE, SULFATE, AND 

BORATE IN THE EXTRACTION OF THORIUM NITRATE 

BY MESITYL OXIDE

Combinations of 1 g Na2HAs04 -12H20 plus 5 mg Th02 , 1 g 

Na2B407 -10H20 plus 5 mg Th02 , and 1 g Na2S04 plus 5 mg Th02 

were separately extracted. The results obtained showed that mesityl 

oxide quantitatively extracts thorium from these combinations. The 

effect of phosphate was studied in more detail. Table 4 shows that 

quantitative results are obtained in the presence of relatively large 

amounts of phosphate.

TABLE 4. Effect of phosphate in the extraction of thorium by mesityl oxide 

[Thorium solutions 2.5 M in Al(NO»)i and 1.2 N In HN08]

(NHOaHPOi

added

(grams)

0.0044

.0088

.0133

.0400

ThOS

added

(grams)

0.0200

.0200

.0200

.0200

ThO>

extracted

(grams)

0.0201

.0200

.0200

.0200

Mol

ratio

P.0t

to

ThOj (i)

2:9

4:0

2:3

2:1

(NHOaHPOi

added

(grams)

0.1200

.2000

.8000

ThO>

added

(grams)

0.0200

.0200

.0200

ThOj

extracted

(grams)

0.0199

.0198

.0198

Mol

ratio

PjOs

to

ThOj (0

6:1

10:1

40:1

' The most likely mol ratio of PaO» to ThOs for monazite is between 2:1 and 6:1.

The conclusions to be drawn from an analysis of the results in 

tables 2, 3, and 4 are as follows:

1. The extraction of thorium nitrate by mesityl oxide when aluminum nitrate is used as the salting agent is quantitative in a single 

extraction. Equilibrium is attained rapidly and the same percentage 

extraction is obtained for both small and large amounts of thorium.

2. Uranium is also extracted quantitatively. Zirconium extracts 

about 70 percent and vanadium about 9 percent in the concentrations 

selected.

3. Yttrium and cerium are incompletely extracted. It is expected 

that erbium will extract in about the same order of magnitude as 

yttrium. The other rare earths extract to an even smaller extent.

4. The mesityl oxide extraction process may be used for the separation of thorium from the rare earths. This separation should be 

especially efficient when thorium is in large excess over the rare earths 

and/or the amount of rare earths is small.

ANALYSIS OF THORIUM ORES 

OUTLINE AND DISCUSSION

1. Decomposition of sample by fusion with a mixture of 

NaF-K2S2 07 .

2. Precipitation of thorium oxalate (separation from U, Nb, and Ti).

3. Separation of rare earths by mesityl oxide extraction, the rare 

earths accompanying thorium being removed from the solvent by 

several washings with aluminum nitrate solution.
182 METHODS OF ANALYSIS, URANIUM AND THORIUM

4. Precipitation of thorium oxalate and ignition to Th02 .

An 0.5-g sample is decomposed in a platinum crucible by fusing 

with 3 g of flux (2 parts by weight NaF, 3 parts by weight K2S207 ). 

This flux is similar to sodium bifluoride and will decompose almost 

all of the refractory minerals associated with thorium.4 After the 

fusion the melt is allowed to cool. Two milliliters of sulfuric acid 

are added (this amount is a little in excess of that required to convert all the NaF to NaHS04) and the crucible is gently heated until 

all the hydrofluoric acid is removed and a clear bisulfate melt is obtained. This process may take as long as 20 minutes. It is most 

important to remove all the hydrofluoric acid (copious fumes of S03 

are evolved in the last stages of heating), as otherwise some thorium 

would be lost as thorium fluoride in the later steps of the procedure. 

The crucible containing the cool melt is immersed in a hot solution 

of oxalic acid and the thorium oxalate is digested on the steam bath 

for about 2 hours.

The thorium oxalate is filtered off on sintered glass and dissolved 

with hot (1 + 1) nitric acid. The residue left on the filter usually 

consists of quartz and, surprisingly, hydrolytic precipitates of 

titanium and zirconium.

It is sometimes difficult for the analyst to be certain of the complete removal of fluorine and the complete conversion of thorium 

fluoride (formed by the action of the flux) to thorium sulfate. Also, 

experience with ores high in titanium, niobium, and tantalum has 

shown that appreciable amounts of these elements precipitate as hydrated oxides rather than dissolve in the oxalic acid. There is a possibility of loss of thorium by the nitric acid failing either to dissolve 

the thorium fluoride or to leach thorium from the mixture of oxalates 

and hydrated oxides.

If these difficulties occur, thev maT be eliminated by certain changes

in the initial steps of the analysis. The most important change is 

the substitution of a hydrofluoric acid precipitation for the first

oxalate precipitation. (Details of this separation are given in part 

20.) This separation is much cleaner if the sequence of operations

before tKe hydrofluoric acid step consist of decomposition of the

sample by fusion with sodium peroxide, solution of the melt in water,

filtration of thorium hydroxide, solution of thorium hydroxide and

its reprecipitation with excess ammonia. The precipitate is then

treated, with, hydrofluoric acid., the thorium fluoride is filtered ancl

decomposed by a potassium pyrosulfate fusion. Thorium hydroxide 

is again precipitated with excess ammonia, filtered and dissolved in

nitric acid. The mesityl oxide separations then follow with no further

changes in the procedure.

4 Some ores may not decompose completely with the KjSjOy-NaF flux. In these instances pure NaF 

should be used.
MESITYL OXIDE EXTRACTION METHOD FOR THORIUM ANALYSIS 183

In our experience the residue was always free from thorium. The 

nitric acid solution of thorium oxalate is evaporated to dryness and 

the residue treated with a little fuming nitric acid to insure the destruction of the oxalate. Aluminum nitrate is added and thorium 

nitrate is extracted with two portions of mesityl oxide. The small 

amounts of rare earths accompanying thorium are separated from 

the organic solvent by three washings with aluminum nitrate solution. The acid concentration of the solution before extraction is not 

too critical and may be as high as 25 percent by volume. Low results were obtained when the concentration of nitric acid was as high 

as 40 percent by volume probably because of oxidation of the solvent. A final thorium oxalate precipitation is made to free thorium 

from the last traces of impurities and the thorium oxalate is ignited 

and weighed as thorium oxide.

DETAILED PROCEDURE

1. Weigh an 0.5-g sample of finely ground ore sample and transfer 

it to a platinum crucible.

2. Add 3 g of flux (2 parts by weight NaF and 3 parts by weight 

of KaS2O7). Mix and fuse the sample over a burner for about 2 

minutes. Cool.

3. Add 2 ml H2SO4 and heat gently over a burner until all tb^ HF 

is removed and a clear bisulfate melt is obtained (in the latter : - "* 

of the heating copious fumes of SO3 should be evolved). Cool.

4. Immerse the crucible and contents in 80 ml of warm oxahY , ' ; 

solution (5 g oxalic acid to 100 ml of water). After the mel> ; : 

disintegrated the crucible is removed, rubbed, and rinsed an*! th 

washings added to the main solution. Bring the solution to a gentle 

boil and boil for 1 minute, stirring the solution continuously.

5. Digest the oxalate (beaker covered) on the steam bath for at 

least 2 hours. There is sometimes a period of induction before the 

thorium oxalate precipitate appears; if no oxalate precipitate is obtained after 2 hours, the solution should be digested preferably 

overnight.

6. Filter (suction) the thorium oxalate on a glass-fritted medium 

filter tube and wash with 2 percent oxalic acid. Reject filtrate.

7. Place a 100-ml beaker under the funnel and dissolve the thorium 

oxalate with three 10-ml portions of hot (1 + 1) HN03 , alternating 

each portion with a limited amount of hot water. Reject residue left 

on the filter.

8. Evaporate the solution to dryness. Add 3 to 4 ml of fuming 

HN03 , cover the beaker, and digest the solution for several minutes 

on the steam bath. Remove the cover and evaporate the solution 

to dryness.
184 METHODS OF ANALYSIS, URANIUM AND THORIUM

9. Take up the residue in 10 ml of HN03 (15+85) warming the 

solution to dissolve the residue. Sometimes a cloud remains. This 

will disappear after the addition of the aluminum nitrate.

10. Add 19 g A1(N03 ) 3 -9H2O and warm the mixture to dissolve the 

crystals. Cool. Pour the solution into a 60-ml separatory funnel.

11. Add 20 ml of mesityl oxide to the beaker containing the original 

solution. Agitate the solution gently and pour the solvent into the 

separatory funnel containing the nitric acid solution of the sample.

12. Shake the funnel vigorously for about 20 seconds and allow 

the layers to separate. Draw off the aqueous layer into a 60-ml 

separatory funnel. Reserve the organic solvent layer.

13. Repeat the extraction of the aluminum nitrate solution with 

10 ml of mesityl oxide and combine the mesityl oxide layers, rejecting 

the aqueous layer.

14. Strip the rare earths from the organic solvent by shaking for 

20 seconds with three separate 20-ml portions of aluminum nitrate 

wash solution [9.5 g A1(NO3) 3 -9H20 to 5 ml of (15+85) HNO31, 

rejecting each wash solution.

15. Strip the thorium from the organic solvent with two 20-ml 

portions of water and transfer the aqueous layers to a 150-ml beaker.

16. Add 1 ml of H2S04 and adjust the volume of the solution to 

about 80 ml. Bring the solution to a gentle boil, add 4 g of oxalic 

acid, and boil gently for 1 minute, stirring continuously. Digest the 

thorium oxalate for at least 3 hours, preferably overnight.

17. Filter the thorium oxalate on no. 40 Whatman filter paper 

and wash with 2 percent oxalic acid solution.

18. Ignite to Th02 (final temperature about 900 C) and weigh.

RESULTS OF ANALYSES

Comparison of the results obtained on eight samples by alternate 

methods of thorium analysis are given in table 5. Method A represents the method of this report, method B is given in part 20, and 

method C is given in part 18. Considering the complexity of the 

materials analyzed, we believe the agreement is satisfactory.

TABLE 5. Analysis of thorium ores

Sample no.

HL1.._ .....

HL2_. .._-...-_- .. _ ..

A-26_. __.._._ _ .......

3063.....-.......-.. .-..

3181 - .

3905-..... 

3924...... ._..

3926..... ................

Description

.. do...... -.

 do... 

Thorite. 

Percent ThOj 1 ''*

Method A

4.19 

4.22 

1.82 

1. 90, 1. 80 

3.40 

2.12 

5.01 

6. 60, 6. 30

Method B

4.18 

4.21 

1.90 

1.90 

3.26 

1.92 

6.15 

6.55

Method C

4.29 

4.26 

1.96

1.98 

5.18

' Method A, mesityl oxide method of this report; method B, method of part 20; method C, method of 

part 18.

o