Fractional Precipitation 

of Rare Earths with 

Phosphoric Acid

GEOLOGICAL SURVEY BULLETIN 1036-N

Fractional Precipitation 

of Rare Earths with 

Phosphoric Acid

By M. K. CARRON, C. R. NAESER, H. J. ROSE, Jr., and F. A. HILDEBRAND

CONTRIBUTIONS TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1036-N

An application of the study

to the geochemistry

of monazite and xenotime

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1958
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. S EATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D. C. - Price 15 cents (paper cover)
CONTENTS

	Page 

Abstract__.____________________________________________ 253

Introduction. _____________________________________________________ 253

Acknowledgment-_________________________________________________ 254

Syntheses of cerium and yttrium phosphates._________________________ 255

Fractional phosphate precipitation of pairs of rare-earth elements______ 256

Methods of preparation._______________________________________ 256

Separation factors.____________________________________________ 257

Spectrochemical determinations____________________________________ 258

Preparation of standards.______________________________________ 258

Apparatus and operating conditions____.___-_____-__----______- 258

Line pairs.___________________________________________________ 259

Precision and accuracy__________________________________.-_--__ 261

X-ray determinations.__-____--___-_____________-_-______-_-_____-_ 263

Results__._._..____________________.._________ 268

Discussion of results.______________________________________________ 270

Literature cited.__________________________________________________ 274

ILLUSTRATIONS

FIGTJKE 44. A typical working curve of the rare-earth pairs___________ 260

45. Variation of separation factors.__________________________ 272

TABLES

TABLE 1. Hydrothermal mineral syntheses_________________________ 255

2. Rare-earth line pairs and the intensity ratios of the standards., 261

3. Precision of spectrochemical determinations.._______----__--- 262

4. Analyses of synthetic unknowns..----.--------------------- 262

5. Spectrochemical analyses and phases produced from fractionally

precipitated lanthanide phosphate pairs.______________---- 263

6. X-ray powder diffraction data for synthetic and natural rareearth phosphates_--_-__-_--_--_-_------_-_----------- 264

7. Hydrothermal syntheses of some single rare-earth phosphates 269

8. Spectrochemical analyses of fractionally precipitated yttrium

and some lanthanide phosphates.____--__------_--------- 270

in

CONTRIBUTIONS TO GEOCHEMISTRY

FRACTIONAL PRECIPITATION OF RARE EARTHS WITH 

PHOSPHORIC ACID

By M. K. CARRON, C. R. NAESER, H. J. ROSE, JR., and F. A.

HlLDEBRAND

ABSTRACT

A study of the fractional precipitation of the phosphates of pairs of adjacent 

and some nonadjacent rare-earth elements was made by means of wet-chemical, 

spectrographic, and X-ray powder diffraction techniques. The order of preferential precipitation in adjacent pairs of lanthanide phosphates was found to be 

La <Ce <Pr <Nd <Sm >Eu >Gd <Tb <Dy <Ho <Er <Tm <Yb >Lu. 

Samarium was found to precipitate preferentially to all the lanthanides of the 

cerium subgroup; ytterbium to all the yttrium subgroup; yttrium to Ce, Sm, Eu, 

and Gd of the cerium subgroup and to dysprosium of the yttrium subgroup, and it 

may be assumed, therefore, to precipitate preferentially to all the lanthanides of 

the cerium subgroup. In this study it was found that paired phosphates in the 

cerium subgroup (lanthanum to gadolinium) had the monazite structure, whereas 

the paired phosphates in the yttrium subgroup (dysprosium to lutetium) had 

the xenotime structure. In the interval comprising gadolinium, terbium, and 

dysprosium (the transition zone), both the monazite and xenotime phases were 

present in these paired phosphates. The results of this study yield information 

regarding the paragenesis and composition of the rare-earth phosphate minerals.

INTRODUCTION

Recent chemical and spectrochemical analyses by the United States 

Geological Survey (Murata and others, 1953, 1957) showed a natural 

fractionation of the rare-earth elements. Considerable variation in the 

proportion of the rare earths was found, and it was shown that this 

could be related to progressive differentiation. This study of fractional precipitation of adjacent pairs of the lanthanides as phosphates 

was expected to provide information regarding the distribution of 

individual lanthanides, and also, the possible mode of formation, and 

order of crystallization and deposition of the phosphate minerals.

Solubility and fractional precipitation studies of the lanthanides in 

such systems as the oxalate (Weaver, 1954c), bromate, sulfate, and 

dimethyl phosphate (Yost and others, 1947) are reported in the litera253
254 CONTRIBUTIONS TO GEOCHEMISTRY

ture, indicating different orders of preferential precipitations. These 

studies were undertaken primarily for their possible application to the 

development of techniques for separating and purifying some of the 

lanthanides. The fractional precipitation studies of the lanthanide 

phosphates presented in this paper were undertaken to obtain fundamental information relating to the geochemistry of rare-earth 

phosphate minerals, such as monazite and xenotime.

A wet-chemical technique was devised for synthesizing single and 

paired lanthanide phosphates and yttrium phosphate, which are 

isostructural with the minerals monazite or xenotime or mixed phases 

of these. The paired lanthanides form an isomorphous solid-solution 

series of the type (AxBy)PO4 , where A and B represent adjacent 

lanthanides, for example, (La, Ce), (Ce, Pr), (Pr, Nd), and so on; 

and x and y are values that indicate the degree of preferential precipitation as determined by analyses of the solutions and precipitates. 

This study is concerned mainly with the ratio x'.y.

In the present work the term "lanthanide" refers to the elements 

having atomic numbers 57 to 71, inclusive, whereas the term "rareearth elements" is used to include yttrium.

In the lanthanide series the paired elements comprising the interval 

from lanthanum to gadolinium are referred to as the cerium subgroup, 

whereas those pairs comprising the interval from dysprosium to 

hitetium are referred to as the yttrium subgroup. The interval 

comprising the paired lanthanides of gadolinium, terbium, and 

dysprosium is defined as the transition zone.

Those phases that were found to be isostructural with monazites 

or xenotimes will be referred to as monazite or xenotime, despite the 

fact that only one or two lanthanides may be present, in contrast to 

the natural monazites and xenotimes which may contain a dozen or 

more lanthanides.

The word "reversal" as used in this paper serves to indicate those 

points where a salt of a heavier lanthanide shows greater solubility 

than the similar salt of the adjacent lighter lanthanide and thereby 

gives a separation factor of a value less than unity.

Weight ratios of the heavier to the lighter rare earths were calculated 

from their oxides. For example, the weight ratios

weight of Ce203 weight of Sm2 03

weight of La^Og weight of Y203

and so on, will be referred to below simply as Ce:La, Sm:Y, and

so on.

ACKNOWLEDGMENT

We are greatly indebted to our colleague, K. J. Murata, for suggesting the study and for numerous stimulating discussions throughout
FRACTIONAL PRECIPITATION OF RARE EARTHS 255

the course of this work. With particular reference to the section on 

"Discussion of results," his interest and close cooperation enabled us 

to arrive at several geochemical relations.

SYNTHESES OF CERIUM AND YTTRIUM PHOSPHATES

Monazite, essentially monoclinic (Ce, La) P04 , and xenotime, tetragonal YP04 , have been synthesized by fusion methods (Palache and 

others, 1951, p. 691, 695). However, to study and evaluate precipitations in the rare-earth phosphate system in relation to natural 

mineral formation, it seemed more desirable to synthesize these minerals hydrothermally by crystallization from aqueous solution in a 

closed system. The method used in the syntheses of monazite and 

xenotime is described under the section on "Fractional phosphate 

precipitation of pairs of rare-earth elements." The results are given 

in table 1.

TABLE 1. Hydrothermal mineral syntheses

Experiment

1. _________

2

3

4

5__

6

7-_________

8__________

9_________-

10________-

11

(*)__.______

«______ 

Constituents '

CeCls, HC1, H8P04 

_do_ . ______ _

do

___-_do_--__-_______

_ do

YC18, HC1, H,P04 _..

_____do_-________---

_____do_____________

_-___do_____-___-___

_____do_-___-_______

do

do

_____do_-_--_.__-___

Temperature 

(degrees 

centigrade)

100 ±3

150±3

200 ±3

250±10

300 ±10

300 ±10

250±10

200 ±3

150±3

105±3

50±3

85±3

95±3

Duration 

(days)

5

5

5

5

5

7

3.5

4

4

4

7

6

7

Predominant phase 

identified

Hexagonal CePOi.

Do.

Do.

Do.

Monazite.

Do.

Do.

Do.

Do.

Do.

Churchite.

1 O.I g of oxide converted to chloride by evaporation to dryness with concentrated hydrochloric acid. 

The salts were dissolved in 2 ml of water containing 0.15 ml of concentrated hydrochloric acid. One ml 

of 2.1 percent (by volume) phosphoric acid was added with sufficient water to make a 4-ml volume.

2 Solution, experiment 11, resealed and rerun.

* Solution, experiment 11, again resealed and rerun.

An aqueous solution of cerous chloride and phosphoric acid, subjected to a temperature of 300°C and at approximately 90 atmospheres 

pressure for 5 days, produced monazite. Under the same conditions, 

yttrium chloride and phosphoric acid formed xenotime.

Attempts to synthesize monazite at temperatures between 100°C 

and 250°C were unsuccessful. The phosphates resulting at these 

lower temperatures gave X-ray powder diffraction patterns identical 

with a cerium phosphate described by Mooney (1950) as a "hexagonal 

modification." This was later found to be isostructural with the 

naturally occurring mineral rhabdophane, a hydrated cerium earth 

group phosphate (Palache and others, 1951, p. 774). A paper con-
256 CONTRIBUTIONS TO GEOCHEMISTRY

cerning a reexamination of this mineral is in preparation by Hildebrand. Xenotime was synthesized at a considerably lower temperature than monazite. Xenotime formed at 105°C; at 95°C the resulting yttrium phosphate was found to be isostructural with the mineral 

churchite (weinschenkite, YP04 .2H20) (Palache and others, 1951, p. 

771).

FRACTIONAL PHOSPHATE PRECIPITATION OF PAIRS OF 

RARE-EARTH ELEMENTS

METHODS OF PREPARATION

The rare earths used throughout these studies were of high purity, 

ranging between 99.0 and 99.8 percent. Ceric oxide was prepared 

by igniting primary-standard ammonium hexanitrato cerate obtained 

from G. Frederick Smith Chemical Co., Columbus, Ohio. Lanthanum, 

praseodymium, and neodymium oxides were obtained from The 

Institute for Atomic Research, Iowa State College, Ames, Iowa; 

samarium, ytterbium, and yttrium oxides from Research Chemicals, 

Inc., Burbank, Calif.; europium, gadolinium, terbium, dysprosium, 

holmium, erbium, thulium, and lutetium oxides from Johnson, Mathey 

Co., London.

The fractionation experiments of pairs of the rare-earth elements 

and the syntheses of the pure minerals described were done in much 

the same manner. Allowing for the higher oxidation state of CeO2 , 

equal amounts of ignited oxides of the pairs were dissolved in hydrochloric acid in a small beaker. The amounts taken were 0.1 g each 

of the less costly oxides, such as those of La, Ce, Pr, Nd, Sna, and Y. 

For the more expensive oxides 0.020 g of each of Eu, Gd, Tb, Dy, Ho, 

Er, Tm, Yb, and Lu were taken. Hydrogen peroxide was added 

to those pairs that included cerium. For each pair the solution was 

evaporated to dryness, and the residue of rare-earth chlorides was 

dissolved in 2 ml of water containing 0.15 ml of concentrated hydrochloric acid. The solution was transferred to a silver crucible (15 

ml true capacity). The beaker was rinsed twice with 0.5 ml of 

distilled water and the rinsings were added to the solution. One 

ml of 2.1 percent by volume phosphoric acid (1 ml of 0.8 percent 

by volume phosphoric acid for the smaller quantities taken) was 

added to the solution. These amounts of phosphoric acid were 

calculated to be enough to precipitate as phosphates one-fourth to 

one-half of the rare-earth elements present. The silver crucible was 

sealed with a thin silver disk and placed in a steel bomb (20 ml 

capacity) which contained 0.5 ml of water to counteract internal pressure. After heating at 300°C ± 10°C for 5 days, the bomb was 

quickly cooled by cold running water. The silver seal was removed 

from the crucible and the fine crystalline phosphates in the solution
FRACTIONAL PRECIPITATION1 OF RARE EARTHS 257

were filtered on a double filter paper, Whatman No. 42, and washed 

six times with distilled water acidified with hydrochloric acid. The 

filtrate was reserved. The phosphates were then sluiced from the 

filter paper with a fine jet of distilled water into a platinum dish. 

The suspension was evaporated to dryness on a steam bath and the 

dried phosphates were removed with a rubber policeman. Portions of 

the phosphates were examined by X-ray powder diffraction methods 

to determine the phases present and their relative unit-cell variations. 

Other portions were analyzed spectrographically to determine the 

ratios of the rare-earth pairs.

In the experiments on fractional precipitation, each reserved filtrate was treated with ammonium hydroxide in considerable excess to 

precipitate the rare earths in solution. Paper pulp was added and 

the solution was filtered after 1 hour through a Whatman No. 40 

filter paper. The precipitate was washed 6 to 8 times with 5 percent 

ammonium hydroxide containing 2 percent ammonium chloride and 

then ignited at 1,000°C. These oxide fractions were also analyzed 

spectrographically to determine the rare earths present. In those 

experiments involving cerium, volumetric determinations of cerium 

in the recovered oxide fractions were also made. These analytical 

determinations permitted the calculation of separation factors. A 

chemical analysis of lanthanum phosphate that was produced in a 

bomb and was found to have the monazite structure by X-ray powder 

diffraction, showed the molecular ratio of La203 to P2 05 to be 1.00 

to 0.97.

SEPARATION FACTORS

Evaluation of results of fractional precipitation processes have been 

expressed by various authors (Weaver, 1954a; Appleton and Selwood, 

1941; Peppard and others, 1953) in terms of separation factors. These 

are empirical numerical values obtained by dividing the weight ratio 

of the elements in the precipitated fraction by the corresponding 

ratio in the unprecipitated fraction.

Our experiments confirmed the claim by Weaver that the separation factor is mathematically independent of the original ratio of 

a mixture of two elements as long as a constant fraction of the total 

is precipitated. Two experiments, in which the cerium to praseodymium starting ratios were 3 to 1 and 1 to 2, showed preferential 

precipitation of praseodymium to cerium in both, with identical 

separation factor values of 1.10. Two other experiments in which 

dysprosium to holmium starting ratios were 2 to 1 and 1 to 2, showed 

preferential precipitation of holmium to dysprosium in both instances, 

with identical separation factors of 1.20. The excellent agreement 

shown here is more fortuitous than real, because the analytical 

method used is accurate to only ±2 percent. For the sake of uni450980 58 2
258 CONTRIBUTIONS TO GEOCHEMISTRY

formity, however, the weight ratio of each pair of the rare-earth oxides 

taken throughout our investigations was 1 to 1.

In the previous section on "Methods of preparation," it will be noted 

that the extent of precipitation of the phosphates of the more costly 

and of the less costly lanthanides varies by a ratio of 2 to 1. The 

purpose of the increased extent of precipitation of the more costly 

materials was to provide a sufficient yield of lanthanide phosphates 

for repeated spectrographic determinations. To ascertain the effect 

of this variation on the separation factor, cerium and lanthanum 

chlorides equivalent to 0.020 g each of their oxides were fractionated 

with 1 ml of 0.8 percent phosphoric acid. The separation factor was 

1.46 as compared with 1.41 obtained in a previous fractionation of 

larger quantities of cerium and lanthanum using the smaller proportion of phosphoric acid. This variation in the separation factor is 

within experimental error and agrees with investigations by Weaver 

(1954a), who fractionated samarium-neodymium mixtures as oxalates 

and found only minor variations in separation factors between 17 

percent and 56 percent precipitation.

SPECTROCHEMICAL, DETERMINATIONS

PREPARATION OF STANDARDS

A series of standards was prepared from high-purity rare earths. 

Three standards were prepared for each rare-earth pair in the experiments on fractional precipitations by weighing exact quantities of each 

rare-earth oxide necessary to give weight ratios of 1.5, 1.0, and 0.67 

of the heavier rare-earth oxide to the lighter rare-earth oxide. All the 

weight ratios of the oxides were based on trivalent rare earths, except 

for Pr and Tb which were calculated from Pr60n and Tb407 . The 

oxides were dissolved in a minimum amount of hydrochloric acid, 

precipitated with an excess of ammonium hydroxide, filtered, and 

ignited. The ignited oxides were then mixed with four parts of pure

graphite.

APPARATUS AND OPERATING CONDITIONS

The apparatus and operating conditions used in this study are as 

follows:

Spectrograph._________ Grating spectrograph with Wadsworth mounting, dispersion 5.0 A/mm.

Cathode._____________ Graphite rod, 3-mm diameter.

Anode______________ Graphite, 6-mm diameter, cavity 4-mm deep, wall

thickness 0.5 mm.

Samples and standards. 4 mg rare-earth oxides+16 mg graphite, 6 mg rareearth phosphates+24 mg graphite. The sample 

weight is 1.5 times greater for the phosphates than 

for the oxides because of the lower content of the 

rare-earth elements in the phosphates.
FRACTIONAL PRECIPITATION OF RARE EARTHS 259

Analytical gap_ _______ 3 mm, maintained throughout excitation period.

Excitation source______ 250 v ballasted d-c arc, 16 amp.

Length of exposure.___ Samples arced to completion.

Emulsion_______ Eastman type III-O, developed 21° C in DK-50 for

5 minutes with continuous agitation.

Wave-length region____ 2300-3500A.

Microphotometer______ Projection comparator-mi cropho to meter using a scanning slit at the plate.

Emulsion calibration. __ Iron line group method of Dieke and Crosswhite (1943).

Exposure index______ Fe 3157.88 A, transmitting 25 percent in an iron arc

exposed for 120 seconds at 5.5 amp.

A 2-step filter transmitting nominally 50 and 100 percent of the 

light was placed at the slit to obtain spectra at 2 different densities. The arc image was focused on the slit at 5.5 magnification, and 

the light from the central 4-mm portion was allowed to enter the slit 

of the spectrograph.

LINE PAIRS

Most of the spectrochemical methods for the determination of rare 

earths have been developed in recent years to test the purity of the 

different rare-earth fractions obtained in purification processes 

(Fassel and others, 1952, 1955; Fassel and Wilhelm, 1948; Norris and 

Pepper, 1952) or to analyze total rare earths which have been chemically concentrated from rocks and minerals (Eose and others, 1954; 

Waring and Mela, 1953). Methods of both categories in general require the use of the more sensitive analytical lines of the individual 

rare-earth elements. The analytical lines used in this study were of 

much weaker intensity because the determined elements were present 

in major amounts.

Spectrographic determinations were made on both the fractionally 

precipitated phosphates and the rare earths which remained in solution. As discussed previously, the rare earths were recovered from 

the filtrate and ignited to the oxides. The weight ratios of the rareearth oxides in the phosphate precipitates and oxides from filtrates 

were expected to fall above and below the 1.0 weight ratio standard 

on the analytical curve. The most important consideration in the 

choice of line pairs was to select a line pair in the 1.0 weight ratio 

standard so that the intensity ratio would be near unity. Many line 

pairs were investigated to find lines close together which would meet 

this requirement. The use of a 2-step filter proved to be invaluable 

since it provided 2 different densities for each line and 4 combinations 

of intensity ratios for each line pair.

The spectra of many of the rare-earth elements are extremely complex and their term analysis has been found to be unusually difficult. 

The term classification data (Albertson and Harrison, 1937; King, 

1928, 1933, 1935, 1939, 1941; Meggers, 1928; Meggers and Scribner,
260 CONTRIBUTIONS TO GEOCHEMISTRY

2.5

2.0

1.5

1.0

.8

.4 .6 .8 1.0 1.5 2.0 2.5

WEIGHT RATIO 

FIGURE 44. A typical working curve of the rare-earth pairs.

1937a, 1937b; Russell, 1950) are incomplete and no information is 

available for some of the analytical lines used. Wherever possible, 

lines of the singly ionized ion were selected. The line pairs used in 

this study are given in table 2. The table includes the intensity ratios 

of the standards which could be useful in any future study of the fractional precipitation of rare-earth pairs. The analytical curves for the 

line pairs are very similar, differing only slightly in their slopes. The 

Dy 3128.409 :Y 3129.933 line pair is shown in figure 44 and represents 

a typical working curve.

The weight ratio of the oxides in Ce:Y phosphate could not be 

datermined directly because the precipitate proved to be extremely 

high in Y and low in Ce. The weight ratio of the oxides in the Ce: Y 

oxides was found to be 1.75, and the weight ratio of the oxides in 

the phosphates was calculated to be 0.07.
FRACTIONAL PRECIPITATION OF RARE EARTHS 261 

TABLE 2. Rare-earth line pairs and the intensity ratios of the standards

Line pair

Ce 113056.777

La II 3104. 589 

Ce I 2874.551

La II 2893. 071 

Pr II 3121. 571

Ce II 3155. 793 

Pr II 3163. 735

Ce II 3154. 506 

Nd 113141.476

Pr II 3121. 571 

Nd 113133.603

Pr II 3168. 242 

Sm 113136.297

Nd 113141.476 

Sm 113136.297

Nd 113134.897 

Eu 113054.930

Sm 113136.297 

Eu 113077.353

Sm 113046.933 

Qd 113089.957

Eu 113054.930 

Qd 113282.257

Eu 113278.54 

Tb 2956. 210

Qd 112923.371 

Tb 3135. 350

Qd 113098.903 

Dy 2913. 952

Tb 2916. 260 

Dy 2948. 323

Tb 2956. 210 

Ho 2610. 51

Dy 2634. 811 

Ho 3038. 690

Dy 3043. 144

Intensity ratios as oxides 

of the standards

1.50

1.49 

1.32

1.26 

1.69

1.65 

1.20

1.21 

1.40

1.31 

1.36

1.21 

1.46

1.17 

1.22

1.21 

1.17

1.24 

1.47

1.00

1.08 

.92

.93 

1.28

1.24 

.92

.88 

1.10

.95 

1.02

.89 

.99

.90 

.96

.93 

.91

.98 

1.16

0.67

0.77 

.65

.67 

.93

.91 

.73

.63 

.88

.67 

.75

.63 

.68

.70 

.76

.73

.69

.79 

.90

Line pair

Er 2765. 617

Ho 2766. 85 

Er 2581. 582

Ho 2610. 51 

Tm 3210. 820

Er 3205. 148 

Tm 2660. 090

Er 2672. 246 

Yb 112718.340

Tm 2742. 960 

Yb 112665.030

Tm 2650. 270 

Lu 113027.290

Yb 113026.668 

Lu I 3080.110

Yb 113093.879 

Sm 113136.297

Y II 3086. 858 

Sm 113117.725

Y I 3114.283 

Qd 113108.364

Y II 3112. 032 

Qd 113040.340

Y I 3045.369 

Eu I 2991.340

Y II 2984. 256 

Eu 113960.230

Y I 2964.968 

Dy 2985. 930

Y I 2984.256 

Dy 3128. 409

Y II 3129. 933 

Yb 113117.804

Y II 3129. 933 

Yb 112983.980

Y I 2984.256

Intensity ratios as oxides 

of the standards

1.50

1.29 

1.22

1.26 

1.11

1.35 

1.20

1.30 

1.20

1.48 

1.29

1.25 

1.72

1.60 

1.56

1.30 

1.34

1.28 

1.20

1.00

1.0 

.97

.94

.87

1.04 

.90

.96 

1.04

1.05 

.96

.95 

1.24

.95 

.95

.94 

1.07

.96

.88

0.67

0.75 

.76

.74 

.70

.84 

.69

.66 

.71

.77 

.72

.72 

.91

.69 

.66

.72

.77

.62 

.62

PRECISION AND ACCURACY

The data on the precision of the method are shown in table 3. 

The coefficient of variation for a single determination is about 2 

percent as calculated from two of the synthetic unknowns exposed in 

duplicate on different plates on different days over a period of several 

months.
262 CONTRIBUTIONS TO GEOCHEMISTRY

TABLE 3. Precision of spectrochemical determination

Rare-earth pair

Sm:Nd_ -_-____---____________.___

Tb:Gd_...__ _...____. __._..

Average

weight

ratio

1.36

90

Number of

determinations

6

6

Coefficient

of variation

2. 1

1.7

The coefficient of variation v is calculated as follows:

v=-

C is the average weight ratio,

d is the difference of the determination from the mean,

n is the number of determinations.

The accuracy of the method was tested by analyzing synthetic 

unknowns prepared in the same way as the standards. The results 

of the tests are given in table 4. The maximum percentage deviation 

from the true value amounted to 3 percent in the determination of 

the Yb:Tm weight ratio. Only two of the rare-earth pairs studied 

by the spectrochemical method were tested by an independent method. 

Cerium was determined volumetrically in the Ce:La and Pr:Ce oxide 

fractions, and the weight ratios compared with those obtained spectrochemically. The volumetrically determined value for Ce:La was 

0.83, and the spectrochemical value, 0.85. The volumetrically 

determined value for Pr:Ce was 0.93, and the spectrochemical value, 

0.95. The agreement between the two methods is good and suggests 

that the accuracy of the spectrochemical determinations is equal to 

the precision.

The results of the spectrochemical analyses of all adjacent pairs 

are given in table 5.

TABLE 4. Analyses of synthetic unknowns

Bare-earth pair (as oxides)

CerLa

SmrNd . _ _______

Eu:Sm_ _______

Tb:Gd____-____--______ _________________

Dy:Tb__-_-_-_--________________. _______

Yb:Tm___ ______________________________

Gd: ¥___-______-_____.__________________

Spectrochemical 

analysis (oxide ratio)

0. 71

1.36

.76

.90

1. 12

1.37

.82

True value (oxide 

ratio)

0. 71

1 33

75

90

1 11

1 33

80
FRACTIONAL PRECIPITATION* OF RARE EARTHS 263

TABLE 5. Spectrochemical analyses and phases produced from fractionally precipitated lanthanide phosphate pairs

Lanthanide pair '

Pr:Ce_ ______

Nd:Pr__.____

Sm:Nd____._

Eu:Sm ____

Gd:Eu___-__-

Tb:Gd__.____

Dy:Tb_____._

Ho:Dy______

Er:Ho_______

Tm:Er__ __

Yb:Tm_--_-

Lu:Yb_______

Average ionic radius 2

1 o0/La ! 22

L 20\Ce 1. 18 

, I7 f0e 1. 18

l-rr 1. ID 

, , ,,?Pr 1. 16

IINCI i. lo 

1 14 fNd 1. 15

1 bin 1. lo 

1 ^rJSm 1. 13

(.till 1. 16

i 11tJEu 1. 12

\\jtQ. 1. 11

. 10 fGdl. 11 i. iu^Tb L 09 

. OR/Tb 1. 09

L 08\Dy 1. 07 

- 0fi fDy 1. 07

I. Mo 1. U5 

Mlr0 !1^

[&r 1. Uo 

i 02 fEr 1. 03

L 02\Tm 1. 01 

, nft(./Tm 1. 01 1. 005|Yb L OQ 

n oo^/Yb 1- 00

0. 995< T Q QQ

^ -LJ Li \J* «7 _/

Ratio in 

phosphate 

precipitate *

} 1.20

} 1.08

1. 11

1. 06

QQ

} .82

1 1. 10

1 1. 10

} 1. 10

} 1. 13

!

1. 16

1. 13

1 91 / ' y

Ratio in 

filtrate 3

0. 85

.95

.92

on

1.06

1. 15

. 93

.94

.90

.83

. 80

.79

1.07

Separation 

factor

1.41

1. 14

1. 21

1. 18

.88

.71

1. 18

1. 17

1.22

1.36

1.45

1.43

.85

Phases 

produced *

M

M

M

M

M

M

M, x

X, m

X

X

X

X

X

» Original oxide ratio is 1.00.

! Individual values of ionic radii from Qoldschmidt (1954).

8 Weight ratio of the heavier lanthanide oxide to the lighter lanthanide oxide.

* M =monazite, -X"=xenotime. 7»=monazite in minor amount. a;=xenotime in minor amount.

X-RAYIDETERMINATIONS

For each of the synthesized lanthanide pairs, a powder diffraction 

pattern was prepared to determine the number and kind of phases 

present as well as to observe by visual comparison the progressive 

contraction of the unit cells from LaP04 to LuP04 in accordance with 

the concept of the lanthanide contraction (Goldschmidt and others, 

1925). The interplanar spacing data for each pattern are shown in 

table 6. The X-ray powder data for LaP04 and LuP04 (cols. 1 and 

20, respectively) have been inserted in table 6 only to show that they 

have the largest and smallest unit cells of all the lanthanides. YP04 

(col. 15) has been inserted to show its relative position with respect 

to the other compounds. Natural monazite from Magnet Cove, 

Ark. (col. 4), and natural xenotime from the Shelby quadrangle, N. C. 

(col. 14), have been inserted to show the relative positions of these 

minerals in the series. Powder patterns of other natural monazites 

and xenotimes were found to vary but little from the data shown in 

columns 4 and 14.
TABLE 6. X-ray powder diffraction data for synthetic and na

Monazite structure

1

LaPO4 

Film 11053

d(A, meas.)

5.22

4.83

4.70

4.19

4.10

3.53

3.31

3.12

3.01

2.88

2.61

2.45

2.42

2.35

2.26

2.21

2.15

2.13

2.04

1.981

1.914

1.884

1.817

1.774

1.755

1.707

1.672

1.634

1.616

1.558 

1.544

1.480

I

3

4

3

13

4

18

85

100

20

35

9

6

9

3

2

20

40

2

2

18

15

1 Q

lo

4

15

11

18

9

5

9

4 

6

4

2

(Oeo.54Lao.4e) 

P04 > 

Film 8280

<Z(A, meas.)

5.21

4.82

4.67

4.18

4.10

3.52

3.30

3.11

3.00

2.88

2.61

2.44

2.40

2.20

2.15

2.13

1.973

1.903

/ 1. 877

\ 1. 870

1.768

1.746

1.701

1.656

1.629

1.610

1. 554 

1.540

1.471

3

(Pro.52Ce0 45)

P041

Film 8352

<Z(A, meas.)

5.20

4.80

4.66

4.17

4.08

3.51

3.29

3.10

2.98

2.87

2.61

2.44

2.40

2.19

2.14

2.13

1.961

1.937

1.895

1.866

1.859

1.759

1.740

1.692

1.647

1.623

1.605

1.549 

1.528

1.465

4

Monazite 

Film 8638

<i(A, meas.)

5.20

4.82

4.66

4.17

4.08

3.51

3.30

3.09

2.99

2 87

2.61

2.44

2.40

2 34

2.25

2.19

2.15

2.13

2.02

1.961

1.933

1.895

1.870

1. 859

1.797

1.762

1.737

1.689

1.645

1.623

1.600

} 1. 535

1.463

I

13

6

18

25

9

25

50

100

18

71

18

18

4

4

2

18

25

25

2

25

6

13

18

18

9

18

25

13

6

6

6

13

4

5

(Ndo.5sPro.47)

PO41

Film 8353

<Z(A, meas.)

5.17

4.78

4.65

4.15

4.08

3.48

3.28

3.09

2.98

2.86

2.59

2.43

2.39

2.18

2.13

2.11

1.957

1.929

1.888

1.866

1.852

1.755

1.731

1.687

1.639

1.618

1.598

5

1.542 

1.519

1.459 

1.447

6

(Smo.52Ndo.4s) 

PO4 > 

Film 8483

d(A, meas.)

5.16

4.75

4.62

4.13

4.04

3.47

3.25

3.06

2.94

2.82

2.57

2.40

2.37

2.16

2.12

2.10

1.941

1.910

1.873

1.855

1.841

1.749

1.719

1.678

1.631

1.610

1.588

1.530 

1.517

1.451 

1.439

(Euo

F

<i(A

j 
FRACTIONAL PRECIPITATION OF RARE EARTHS 265

Cot- CO 

CD^ t-< 

CCCCCO

j-< COM CO M 

Ofl T-H T I O O

1-HrH O

N IO ^*

CO 00 O 

CO W«JI

COI^COIM

Mrt -4 rH
TABLE 6. X-ray powder diffraction data for synthetic and natural r

Xenotime Structure

11

(Tbo.52 

Gd0 .48)P04l

Film 8532

d (A, meas.)

3.45

2.46

12

(Dyo.K 

Tbo.48)PO4i 

Film 8593

d (A, meas.)

4.58

3.45

2.75

2.57

2.44

2.27

2.16

1.941

1.828

1.774

1.728

1.695

1.621

1.547

1.523

1.439

1.391

1.352

1.295

1.241

1.225

1.159

1.143

1.131

1.119

1.107

1.096

1.086

1.018

.9906

13

(HOC .82

Dyo.48)P04i 

Film 8811

d (A, meas.)

4.55

3.45

2.56

2.44

2.27

2.15

1.933

1.831

1.771

1.728

1.687

1.618

1.549

1.517

1.435

1.351

1.287

1.244

1.154

1.126

1.117

1.105

1.094

1.082

1.024

1.016

. 9877<«

14

Xenotime 

Film 8718

d (A, meas.)

4.55

3.45

2.75

2.56

2.44

2.27

2.15

1.929

1.824

1.768

1.725

1.684

1.616

1. 543ai

1. 513at

1. 432ai

1. 383a!

1. 346«i

1. 283ai

1. 235«*i

1. 221ai

1. 150«*i

1. 137ai

1.124ai

1. 114<*i

1. 102ai

1.091ai

1. OSOai

1. 022ai

1. 014ai

. 9890<*i

. 9849<xi

I

25

100

9

50

13

6

25

9

13

50

18

6

3

9

2

9

6

4

9

9

2

6

4

2

.7

4

3

6

.5

.7

.3

3

15

YPO4 

Film 8939

d (A, meas.)

4.53

3.43

2.73

2.55

2.43

2.26

2.14

1.926

1.821

1.762

1.722

1.681

1.540

1.506

1. 431ai

1. 377<*i

1. 343«i

1. 280«*i

1.233ai

1. 220«*i

1.148ai

1. 121ai

1. 113<*i

1. 099*!

1.089ai

1. 077ai

.9829ai

I

30

100

3

50

13

15

25

20

13

50

15

4

6

3

11

11

4

15

7

1

3

2

1

4

2

7

7

16

(Ero.53

H00 .47)PO4'

Film 8852

d (A, meas.)

4.53

3.43

2.73

2.55

2.42

2.26

2.14

1.926

1.817

1.762

1.719

1.537

1.508

1.427

1.377

1.341

1.280

1.230

1.216

1.145

1.120

1.110

1.098

1.086

1.075

.9816

1

(Tm

Ero.4e

Film 

d (A, m

4.51

3.43

2.73

2.55

2.42

2.25

2.13

1.92

1.81

1.75

1.71

1.53

1.50

1.42

1.37

1.33

1.22

1.21

1.14

1.12

1.10

1.09

1.08

1.07

.98
.9621

.9541

.9332

.9197

.8890ai

.8720ai

.8656ai

.8516ai

.8402ai

.8166*!

. 9594ai

. 9497ai

. 9313ai

. 9153ai

.8863ai

.8786ai

.8704ai

.8316ai

.8085aj

. 7870ai

,7768a4

. 9576ai

. 9491ai

. 9291ai

.9138ai

.8846ai

.8680ai

. 8633ai

.8555aj

. 8478ai

. 8371ai

.8305ai

.8074ai

.7876ai

. 7858ai

. 7755ai

2

2

4

2

2

2

1

.7

.5

1

.7

4

.3

.7

.1

. 9557ai

. 9461ai

.9118ai

.8828ai

. 8672ai

.8541ai

.8465ai

.8284ai

.8120a,

. 8061ai

.7863ai

.7843ai

2

2

5

4

4

1

.9

1

.9

5

.9

2

. 9533ai

. 9449ai

. 9103ai

.8815ai

.8645ai

.8592ai

.8534ai

. 8451ai

. 8365ai

. 8050ai

. 9

.94

.90

.87

. 8

. 8

.85

.84

. 8

i Weight ratios of the elements calculated from the weight ratios of the oxides in the phosphate precipitat

» Prom A. Pabst, Am. Min. v. 36, no. 1-2,1951, p. 6 

» From Am. Soc. Testing Materials. Card 5-0454.
268 CONTRIBUTIONS TO GEOCHEMISTRY

The diffraction patterns were taken with Debye-Scherrer powder 

cameras (114.59 mm diameter) using the Straumanis technique with 

CuKa (Ni filter), X= 1.5418 A. X for K«i = 1.5405. The cut-off 

point for these cameras is at a 20 value of approximately 5°. Measurements were made with a Hilger-Watts film-measuring rule with a 

vernier precision of 0.05 mm. Shrinkage corrections were determined 

and appropriately applied to each film. Intensities were measured 

with calibrated film strips prepared such that successive step exposures are related to each other by a factor of -\/2. Intensity values 

were not measured for all the synthetic products because many of 

them showed the effects of preferred orientation. Because the intensity relationships are not pertinent to the problem at hand, no 

attempts were made to eliminate the preferred orientation condition. 

Most of the synthetic products contained a moderate to large amount 

of AgCl and a small amount of Ag (contaminants from the silver 

crucible), but these phases were readily recognizable and did not 

conflict with interpretation and measurement of the powder patterns.

BESTJLTS

In table 5 are given spectrochemical results and phases produced 

in all the fractionation experiments of adjacent pairs of the entire 

suite of lanthanides. Separation factors were calculated for each 

lanthanide pair. Also shown are average ionic radii of the pairs, 

which are simple arithmetic means of values as given by Goldschmidt 

(1954, p. 89). The fractionation experiments indicate that the 

lanthanide phosphates obtained by this procedure form monazite, 

xenotime, or mixtures of both phases and that fractional precipitation 

in this system is a preferential process. Of those lanthanides that 

form monazite only, the heavier ones precipitated in preference to 

the lighter ones. A reversal occurred with the Eu, Sm pair, where 

the lighter lanthanide, Sm, precipitated preferentially to the heavier, 

Eu. This reversal continued through the Gd,Eu pair. With Tb,- 

Gd the order of preferential precipitation reverted to the heavier 

lanthanide, Tb, and a mixture of xenotime and monazite appeared, 

with monazite predominating. At Dy,Tb the heavier lanthanide, 

Dy, precipitated preferentially to Tb and again a mixture of xenotime 

and monazite appeared, but with the xenotime phase predominating. 

At Ho,Dy all evidence of the monazite phase disappeared. Preferential precipitation continued to favor the heavier lanthanide of the 

pairs until the Lu,Yb pair where another reversal is evident.

The X-ray diffraction data in table 6 show that the monazite 

phase was produced in each pair from (Ce,La)PO4 (col. 2) through 

(Dy,Tb)PO4 (col. 10), whereas the xenotime phase was produced in 

pairs from (Tb,Gd)PO4 (col. 11) through (Lu,Yb)PO4 (col. 20). In
FRACTIONAL PRECIPITATION OF RARE EARTHS 269

the pairs (Tb,Gd)PO4 and (Dy,Tb)PO4 (cols. 9, 10, 11, and 12) in the 

transition zone, both of these phases were present (table 5) so that 

the pairs in columns 9 and 10 showing the data for the monazite 

phase were repeated in columns 11 and 12 to show the data for the 

xenotime phase. In this transition zone the Tb,Gd pair consisted 

predominantly of the monazite phase with a small amount of the 

xenotime phase whereas the adjacent Dy,Tb pair consisted predominantly of the xenotime phase with a small amount of the monazite 

phase.

To determine more precisely the transition point between the cerium 

subgroup with the monazite structure and the yttrium subgroup with 

the xenotune structure, bomb preparations of the single rare-earth 

phosphates of Sm, Eu, Gd, Tb, Dy, and Y were made (table 7). X-ray 

examinations of these show that SmPO4 (bomb 32), EuPO4 (bomb 

26), and GdPO4 (bombs 27 and 38) have the monazite structure 

and TbPO4 (bomb 31), DyPO4 (bombs 34 and 78) and YPO4 (bomb 

30) have the xenotime structure. With particular reference to TbPO4 

produced in glass ampoules (bombs 28 and 56), the ampoules broke 

during the experiments, but the recovered products, which included 

bits of glass and perhaps iron chloride, were found by X-ray examination to have the monazite structure. This demonstrates that TbPO4 

ma}r be dimorphic because it acquired the xenotune structure when 

prepared in silver crucibles and the monazite structure when prepared 

in glass ampoules. This also establishes the transition point in the 

lanthanide series at TbPO4 .

TABLE 7. Hydrothermal syntheses of some single rare-earth phosphates

Bomb

32

26

27

38

28

31

56

34

78

30

Rare-earth 

oxide l

Sm2O3

Eu2O3

Gd2O3

Gd2O3

Tb4 07

Tb4O7

Tb4 07

Dy2 03

Dy2 03

YaO*

Weight of oxide taken 

(gram)

0.027

.015 __ __ - ^ ___

.015-- - -

.028 -_ _

.012 _

.017 -- -

.015 -- -

.019

.025( + 0.2gSiO2)----

.02________. ________

Type of container

Silver crucible _

Glass ampoule.

do

Glass ampouleSilver crucible _

Silver crucible

___ -_do- _-_ 

 __do_- _ 

Predominant phase* 

produced

Monazite.

Do.

Do.

Do.

Do.

Xenotime.

Monazite.

Xenotime.

Do.

Do.

1 Each oxide was converted to chloride by evaporation to dryness with concentrated hydrochloric acid. 

The salts were taken up in 2 nil of water containing 0.15 ml of concentrated hydrochloric acid. One ml of 

0.8 percent (by volume) phosphoric acid was added with sufficient water to make a 4-ml volume. Each 

was heated at 300°C_d-10°C, 90 atmospheres pressure,.for S.days.

The relation of yttrium phosphate to the lanthanide phosphates can 

be seen from the results of fractionation experiments given in table 8. 

It may be assumed that yttrium will precipitate preferentially to all 

the lanthanides of the cerium subgroup because it was shown that
270 CONTRIBUTIONS TO GEOCHEMISTRY

yttrium is precipitated preferentially to dysprosium of the yttrium 

subgroup. This assumption is further justified by the fact that in the 

experiment with the Ce,Y pair, the solid phase was sufficiently enriched in yttrium, so that no evidence of a monazite phase was detected. In the experiments with the Sm,Y and the Eu,Y pairs, there 

was evidence of the monazite phase, but the weight ratios indicate 

predominance of the xenotime phase in both pairs. It might be 

expected that the experiment with the Gd,Y pair would also show two 

phases, but only the xenotime phase was detected. Ytterbium was 

found to precipitate preferentially to yttrium, thus placing yttrium 

in the phosphate system between dysprosium and ytterbium. Comparison of the relative unit-cell sizes from X-ray powder diffraction 

patterns more definitely established the position of yttrium phosphate 

at the Er,Ho pair. Assuming that only the xenotime phase would 

be present, X-ray powder diffraction patterns were not made of the 

Dy,Y and Yb,Y pairs.

TABLE 8. Spectrochemical analyses of fractionally precipitated yttrium and some

lanthanide phosphates

[Heated at 300°C for 5 days]

Lanthanide and yttrium pairs

Ce:Y«_. ._.._ ..__ .___..._..

Sm:Y »_ .__.__ __.._....__.._

Eu:Y 8

Gd:Y«._.___. _____._..._.___.

Dy:Y<L___ __.._._.___. ___.._

Yb:Y ________ _______________

Ratio in 

phosphate 

precipitate 1

*0 07

56

82

60

80

1 60

Ratio in 

filtrate '

1.75

1. 30

1. 33

1. 35

1. 15

. 67

Separation 

factor

0 04

43

62

44

70

2 39

Phases 

present 3

X

X + M

X + M

X

i Weight lanthanide oxide: weight yttrium oxide. 

3 X=xenotime, M monazite.

3 0.1 gram of each oxide was converted to chlorides, dissolved in 3 ml of water containing 0.15 ml of concentrated hydrochloric acid, and then 1 ml of 2.1 percent (by volume) phosphoric acid was added.

4 Calculated from the oxide ratio in the filtrate.

8 0.02 gram of each oxide was treated as in footnote 3 except that 1 ml of 0.8 percent (by volume) phosphoric 

acid was added. 

8 0.05 gram of each oxide was treated as In footnote 3.

DISCUSSION OF RESULTS

In fractional precipitation studies, preferential precipitations indicate the relative solubility of analogous compounds of two or more 

elements. The compounds of the lanthanide elements are ideal for 

such studies inasmuch as they form an extended series containing 

elements closely related structurally and chemically. In this investigation the heavier lanthanide of the pairs exhibited greater 

insolubility, reaching maximum insolubility at samarium in the 

cerium subgroup and at ytterbium in the yttrium subgroup. While 

the greater insolubility of the heavier lanthanide may be explained,
FRACTIONAL PRECIPITATION OF RARE EARTHS 271

in part, as a function of decreasing ionic radius, the reversals in 

solubility shown with Eu, Gd, and Lu offer contradictory evidence 

to this concept. The need for a more adequate explanation of these 

reversals is apparent. It is noteworthy that in the transition zone 

from the monazite structure to the xenotime structure two phases 

were observed in the X-ray patterns. Under the microscope these 

two-phase products were observed to have a needlelike habit; no other 

morphological forms could be observed. The Tb,Gd pair, which was 

predominantly monazite, and the adjacent Dy,Tb pair, which was 

predominantly xenotime, formed these needlelike crystals. The other 

adjacent pair, Eu,Sm, which was all monazite, showed an irregular 

shape characteristic of all other lanthanide pah's.

Reversals in most systems involving the lanthanides appear to be 

the rule rather than the exception. Except for the dimethyl phosphate system at 25°C in which the solubility of the lanthanides falls 

steadily from lanthanum to ytterbium, the lanthanide salts generally 

show reversals (Yost and others, 1947). In theoxalate system (Weaver, 

1954c) the solubility decreases to a minimum at samarium, followed 

by increasing solubility that persists through ytterbium. The 

systems R2 (SO4 ) 3 .8H2 0 at 20°C and R(Br03 ) 3 .9H2O, where R is the individual lanthanide or yttrium, also show decreasing solubilities of the 

lanthanides from praseodymium and lanthanum to europium and 

gadolinium, respectively (Yost and others, 1947), followed by increasing solubilities that continue through lutetium and terbium.

The variation of separation factor values of the heavier to the 

lighter of each lanthanide pair is shown in figure 45. Preferential 

precipitation of the heavier to the lighter lanthanide is indicated by 

a separation factor greater than 1.00. Values less than 1.00, as shown 

by the Sm,Eu and Yb,Lu pah's, indicate 2 reversals in solubilities 

with maximum insolubilities at samarium and ytterbium, respectively. 

The Eu,Gd pair, for which the value is also less than 1.00, is interpreted as a continuation of the reversal at the Sm,Eu pair. Experimental studies now in progress indicate that these data may be used 

for predicting preferential precipitations of widely separated pairs. 

Details will be published later.

The position of yttrium in the lanthanide series has been variously 

reported in different studies (Kettelle and Boyd, 1947; Vickery, 1953; 

Weaver, 1954b) to be between Tb and Tm. X-ray diffraction patterns 

provide an excellent means for measuring the lanthanide contraction 

(Goldschmidt and others, 1925). This is a unique property of the 

series, related to continual diminishing size of the ionic radii of the 

lanthanides. In the phosphate system each successive pair of adjacent 

lanthanides showed smaller unit cells as the mean ionic radius of the 

pair decreased. From the powder data it can be seen that yttrium
272 CONTRIBUTIONS TO GEOCHEMISTRY

1.50

1.40

1.30

1.20

1.10

1.00

0.90

0.80

0.70

La 'Ce Ce,Pr Pr'Nd Nd,Sm Sm'Eu Eu,Gd Gd'Tb Tb,Dy Dy' Ho Ho.Er Er'Tm Tm.Yb 

ADJACENT LANTHANIDE PAiRS

FIGUBE 45. Variation of separation factors. 

Weight of heavier lanthanide oxide

Separation factor=-

Weight of lighter lanthanide oxide

Weight of heavier lanthanide oxide 

Weight of lighter lanthanide oxide

in precipitate

in nitrate

phosphate has unit-cell dimensions very close to that of the Ho,Er 

pair.

Our experiments have shown that at moderate temperature (300°C) 

and pressure (approximately 90 atmospheres) yttrium phosphate precipitates preferentially to all the cerium subgroup lanthanides. Hence, 

from solutions containing yttrium and all other lanthanides, initial 

precipitates should tend to be rich in yttrium. With regard to mineralogical significance this finding is supporting evidence for judging the 

sequence of crystallization and deposition of the natural minerals. 

Bj0rlykke (1935) postulated simultaneous crystallization of monazite 

and xenotime. Assuming that the natural process is one of fractionation under conditions of moderate temperatures and pressures, then,
FRACTIONAL PRECIPITATION OF RARE EARTHS' 273

as yttrium forms xenotime, our experiments indicate that xenotime 

would fractionally crystallize first. Yttrium and the lanthanides of its 

subgroup would be expected to combine first with any phosphorus 

present, coprecipitating only minor amounts of the cerium subgroup 

lanthanides. Additional phosphorus would then lead to the formation 

of monazite with a major quantity of the cerium subgroup lanthanides. 

However, taking into account the complex systems from which minerals form in nature, the possibility of prior deposition of monazite 

cannot be precluded. Future crystallization studies of systems more 

complex than the simple one presented here may indicate such order 

of deposition.

Of special interest regarding the hexagonal cerium phosphate produced between 100°C and 250°C and the natural occurring mineral 

rhabdophane are the results of three experiments. Solutions containing cerium chloride, phosphoric and hydrochloric acids, in the 

amounts used in the silver crucible syntheses, were sealed in Pyrex 

test tubes and kept immersed in a steam bath (approximately 97°C) 

for 5 days, 4 months, and 1 year, respectively. The phosphates from 

the first two experiments gave X-ray powder diffraction patterns 

isostructural with hexagonal cerium phosphate and rhabdophane. The 

phosphates that remained for 1 year were isostructural with monazite 

(monoclinic), confirming Mooney's (1950) claim that long digestion 

periods tend to cause conversion to the monoclinic form. These experiments demonstrated that a phosphate isostructural with monazite 

can be produced at a much lower temperature and pressure if given 

sufficient time.

In other experiments, natural occurring rhabdophane from Salisbury, Conn. (Palache and others, 1951, p. 774), was converted to 

monazite, and churchite, described as weinschenkite from the Kelly 

Bank mine, Vesuvius, Va. (Milton and others, 1944), was converted to 

xenotime by sealing the minerals in silver crucibles containing 4 ml of 

water and heating at 300°C for 5 days. The radial fibrous crystal 

habit of both rhabdophane and churchite was maintained in these 

experiments, showing that pseudomorphism of monazite and xenotime 

may be possible in the natural minerals, although such evidence of 

pseudomorphism has not been observed in nature.

It seems from these experiments that both rhabdophane and 

churchite are less stable than monazite and xenotime, respectively. 

Therefore, it is not unlikely that some present monazite and xenotime 

samples were precipitated initially as rhabdophane or churchite.
274 CONTRIBUTIONS TO GEOCHEMISTRY

LITERATURE CITED

Albertson, W. E., and Harrison, G. R., 1937, Preliminary analysis of the first 

spark spectrum of cerium, Ce II: Phys. Rev., v. 52, p. 1209-1215.

Appleton, D. B., and Selwood, P. W., 1941, Fractional partition of the rare 

earths: Am. Chem. Soc. Jour., v. 63, p. 2029.

B0rlykke, Harald, 1935, The mineral paragenesis and classification of the granite 

pegmatites of Iveland, Setesdal, Southern Norway: Norsk. Geol. Tidsskr., 

v. 14, p. 211-309.

Dieke, G. H., and Crosswhite, H. M., 1943, The use of iron lines as intensity 

standards: Optical Soc. America Jour., v. 33, no. 8, p. 425-434.

Fassel, V. A., Cook, H. D., Krotz, L. C., and Kehres, P. W., 1952, Quantitative 

spectrographic analysis of the rare-earth elements. IV. Determination of 

cerium, praseodymium, and neodymium in lanthanum, V. Determination 

of lanthanum, praseodymium, and neodymium in cerium, VI. Determination of lanthanum, cerium, and neodymium in praseodymium, VII. Determination of praseodymium in neodymium: Spectrochimica Acta, v. 5, p. 

201-209.

Fassel, V. A., Quinney, Beverly, Krotz, L. C., and Lentz, C. F., 1955, Quantitative 

spectrographic analysis of rare-earth elements. Determination of holmium, 

erbium, yttrium, and terbium in dysprosium, Determination of yttrium, 

dysprosium, and erbium in holmium, and Determination of yttrium, dysprosium, holmium, thulium, and ytterbium in erbium: Anal. Chemistry, 

v. 27, p. 1010-1014.

Fassel, V. A., and Wilhelm, H. A., 1948, Quantitative spectrographic analysis of 

the rare-earth elements. I. Determination of samarium in neodymium, II. 

Determination of europium in samarium: Optical Soc. America Jour., v. 

38, p. 518-526.

Goldschmidt, V. M., 1954, Geochemistry, London, Oxford Univ. Press, p. 730.

Goldschmidt, V. M., Earth, Tom, and Lunde, G., 1925, Geochemische Verteilungsgesetze der Elemente. V. Isomorphie und Polymorphie der Sesquioxyde. Die Lanthaniden-Kontraktion und ihre Konsequenzen: Norske 

vidensk.-akad. Oslo, v. 5, Mat.-Nat. Kl. 1, p. 7.

Kettelle, B. H., and Boyd, G. E., 1947, The exchange adsorption of ions from 

aqueous solutions by organic zeolites. IV. The separation of the yttrium 

group rare earths: Am. Chem. Soc. Jour., v. 69, p. 2800-2812.

King, A. S., 1928, Temperature classification of the stronger lines of cerium and 

praseodymium: Astrophys. Jour., v. 68, p. 194-245.

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 1935, Temperature classification of samarium lines: Astrophys. Jour., v. 

82, p. 140-191.

 1939, Temperature classification of europium lines: Astrophys. Jour., v. 

89, p. 377-430.

1941, Temperature classification of thulium lines: Astrophys. Jour., v.

94, p. 226-231. 

Meggers, W. F., 1928, Wave lengths and Zeeman effects in yttrium spectra: U. S.

Natl. Bur. Standards Jour. Research, v. 1, p. 319-341. 

Meggers, W. F., and Scribner, B. F., 1937a, Arc and spark spectra of lutecium:

U. S. Natl. Bur. Standards Jour. Research, v. 19, p. 31-39. 

 1937b, Arc and spark spectra of ytterbium: U. S. Natl. Bur. Standards

Jour. Research, v. 19, p. 651-664.
FRACTIONAL PRECIPITATION OF RARE EARTHS 275

Milton, Charles, Murata, K. J., and Knechtel, M. M., 1944, Weinschenkite,

yttrium phosphate dihydrate, from Virginia: Am. Mineralogist, v. 29, p. 92-

110. 

Mooney, R. C. L., 1950, X-ray diffraction study of cerous phosphate and related

crystals. I. Hexagonal modification: Acta Crystallographica, v. 3, p. 337-

354. 

Murata, K. J., Rose, H. J., Jr., and Carron, M. K., 1953, Systematic variation of

rare earths in monazite: Geochim. et Cosmochim. Acta, v. 4, p. 292-300. 

Murata, K. J., Rose, H. J., Jr., Carron, M. K., and Glass, J. J., 1957, Systematic

variation of rare-earth elements in cerium-earth minerals: Geochim. et

Cosmochim. Acta, v. 11, p. 141-161. 

Norris, J. A., and Pepper, C. E., 1952, Quantitative speetrochemieal analysis of

rare-earth mixtures: Anal. Chemistry, v. 24, p. 1399-1403. 

Palache, Charles, Berman, Harry, and Frondel, Clifford, 1951, Dana's system of

mineralogy, 7th ed., v. 2: New York, John Wiley and Sons, Inc., 1124 p. 

Peppard, D. F., Faris, J. P., Gray, P. R., and Mason, G. W., 1953, Studies of the

solvent extraction behavior of the transition elements. I. Order and degree

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p. 294-301. 

Rose, H. J., Jr., Murata, K. J., and Carron, M. K., 1954, A chemical-spectrochemical method for the determination of rare-earth elements and thorium in

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Russell, H. N., 1950, The arc and spark spectra of gadolinium: Optical Soc.

America Jour., v. 40, p. 550-575. 

Vickery, R. C., 1953, Chemistry of the lanthanons: New York, Academic Press,

Inc., p. 205. 

Waring, C. L., and Mela, Henry, Jr., 1953, Method for determination of small

amounts of rare earths and thorium in phosphate rocks: Anal. Chemistry,

v. 25, p. 432-435.

Weaver, Boyd, 1954a, The separation factor. A criterion for evaluation of fractional separation processes: Anal. Chemistry, v. 26, p. 474-475.

 1954b, Fractional separation of rare earths by precipitation with mandelic 

acid: Anal. Chemistry, v. 26, p. 476-478.

 1954c, Fractional separation of rare earths by oxalate precipitation from 

homogeneous solution: Anal. Chemistry, v. 26, p. 479-480.

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and their compounds: New York, John Wiley and Sons, Inc., p. 42.

U. S. GOVERNMENT PRINTING OFFICE.1958

Contributions to 

Geochemistry 1955-57

GEOLOGICAL SURVEY BULLETIN 1036

This bulletin was printed 

as separate chapters A-N

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1958
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director
CONTENTS

[The letters In parentheses preceding the titles designate separately published chapters]

Page

(A) Rapid field and laboratory method for the determination of copper

in soil and rocks, by Hy Almond____________________________ 1

(B) Rapid determination of germanium in coal, soil, and rock, by Hy

Almond, Harry E. Crowe, and Charles E. Thompson.___________ 9

(C) Rapid analysis of silicate rocks, by Leonard Shapiro and W. W.

Brannock._________________________________________________ 19

(D) Correlation of dioctahedral potassium micas on the basis of their

charge relations, by Margaret D. Foster_______________________ 57

(E) An application of spectrographic microphotometric scanning, by C. L.

Waring, Mona Franck, and A. M. Sherwood_________________ 69

(F) A spectrographic method for determining the hafnium-zirconium

ratio in zircon, by C. L. Waring and H. W. Worthing.__________ 81

(G) X-ray powder data for uranium and thorium minerals, by Clifford

Frondel, Daphne Riska, and Judith Weiss Frondel____________ 91

(H) The occurrence of minor elements in ash of low-rank coal from

Texas, Colorado, North Dakota, and South Dakota, by Maurice

Duel and C. S. Annell__________________________ 155 

(I) Colorimetric determinations of traces of bismuth in rocks, by F. N.

Ward and H. E. Crowe_________________________ 173 

(J) Field determination of uranium in natural waters, by F. N. Ward and

A. P. Marranzino___________________________ _____ 181

(K) Differential thermal analysis of selected borate minerals, by Robert

D. Allen_________________________________________________ 193

(L) A field chromatographic method for determination of uranium in

soils and rocks, by Charles E. Thompson and H. W. Lakin________ 209

(M) Model '54 transmission and reflection fluorimeter for determination

of uranium with adaptation to field use, by E. E. Parshall and

L. F. Rader, Jr______ _______ ___________________ 221 

(N) Fractional precipitation of rare earths with phosphoric acid, by

M. K. Carron, C. R. Naeser, H. J. Rose Jr., and F. A. Hildebrand. 253

in