o1 SW«»Ta*

NBS MISC. PUBL 260-8

Standard Reference Materials:

ANALYSIS OF URANIUM CONCENTRATES AT THE

NATIONAL BUREAU OF STANDARDS

National Bureau of Standards
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology" in industry and commerce. Its responsibilities include development and maintenance of the national standards of measurement, and the provisions of means for making measurements consistent with

those standards; determination of physical constants and properties of materials; development of methods for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices

for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance to industry, business, and consumers in the development and acceptance of commercial standards and simplified trade practice recommendations; administration of programs in cooperation with United States business groups and standards organizations for the development of

international standards of practice; and maintenance of a clearinghouse for the collection and dis- semination of scientific, technical, and engineering information. The scope of the Bureau's activities

is suggested in the following listing of its three Institutes and their organizational units. Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics.

Heat. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards Laboratory:* Radio Standards Physics; Radio Standards Engineering. Office of Standard Reference Data.

Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic

Materials. Reactor Radiations. Cryogenics.* Materials Evaluation Laboratory. Office of Standard Reference Materials. Institute for Applied Technology. Building Research. Information Technology. Performance Test Development. Electronic Instrumentation. Textile and Apparel Technology Center. Technical Analysis. Office of Weights and Measures. Office of Engineering Standards. Office of Invention and Innovation. Office of Technical Resources. Clearinghouse for Federal Scientific and Technical Information.**

* Located at Boulder, Colorado, 80301. ** Located at 5285 Port Royal Road, Springfield, Virginia, 22171.

Library of Congress Catalog Card Number : 65-62743
UNITED STATES DEPARTMENT OF COMMERCE • John T. Connor, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Standard Reference Materials:

Analysis of Uranium Concentrates

at the National Bureau of Standards

M. S. Richmond

Institute for Materials Research

National Bureau of Standards Washington, D.C.

National Bureau of Standards Miscellaneous Publication 260-8

Issued December 1, 1965

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C, 20402 - Price 55 cents
Library of Congress Catalog Card Number: 65-62743
PREFACE

Within the framework of the NBS Institute for Materials

Research the area of standard reference materials is a broad

and important one, including the preparation, characterization and distribution of a wide variety of materials in such

diverse fields as metallurgy, polymers and inorganic

materials. In carrying out such a program there is much

interaction with representatives of industry and science,

beginning with discussions as to which primary standard

materials will do most to advance technology, the furnishing

of materials and fabrication of samples, and the characterization and certification of the materials by cooperative

efforts. The many groups participating in a standards

program are very ihterested in detailed information on specific aspects of the program — but to date there has

been no publication outlet for such written discussions.

To meet this need, NBS Miscellaneous Publication 260

has been reserved for a series of papers in the general area

of "standard reference materials". This series will present

the results of studies and investigations undertaken within

the Institute for Materials Research with emphasis on the

preparation and characterization of standard reference

materials. This subject-oriented series will provide a means for rapid dissemination of this detailed information

and we hope will stimulate the use of standard reference

materials in science and industry.

W. Wayne Meinke, Chief

Office of Standard Reference Materials

iii
OTHER NBS PUBLICATIONS IN THIS SERIES

NBS Misc. Publ. 260, Standard Reference Materials: Catalog

and Price List of Standard Materials Issued by the National

Bureau of Standards, October 1965. 45 cents.* (Supersedes

NBS Misc. Publ, 24l, March 1962.)

NBS Misc. Publ. 260-1, Standard Reference Materials:

Preparation of NBS White Cast Iron Spectrochemical

Standards, June 1964. 30 cents.*

NBS Misc. Publ. 260-2, Standard Reference Materials:

Preparation of NBS Copper-Base Spectrochemical Standards,

October 1964. 35 cents.*

NBS Misc. Publ. 260-3, Standard Reference Materials:

Metallographic Characterization of an NBS Spectrometric

Low-Alloy Steel Standard, October 1964. 20 cents.*

NBS Misc. Publ. 260-4, Standard Reference Materials:

Sources of Information on Standard Reference Materials,

February 1965. 20 cents.*

NBS Misc. Publ. 260-5, Standard Reference Materials:

Accuracy of Solution X-Ray Spectrometric Analysis of

Copper-Base Alloys, March 1965. 25 cents.*

NBS Misc. Publ. 260-6, Standard Reference Materials:

Methods for the Chemical Analysis of white Cast Iron

Standards, July 1965. 45 cents.*

NBS Misc. Publ. 260-7, Standard Reference Materials:

Methods for the Chemical Analysis of NBS Copper-Base

Spectrochemical Standards. In press.*

I

* Send orders with remittance to: Superintendent of

Documents, U. S. Government Printing Office, Washington,

D. C. 20402. Remittance from foreign countries should

include an additional one-fourth of the purchase price

for postage.

iv
CONTENTS

PAGE

1. INTRODUCTION ........ 2

2. THE PROBLEM OF SAMPLING WEIGHT BASE LINE .... 6 Basis of Choice 6 Historical Review 7 NBS Studies 9 Resolving the Base Line Problem 18

Effectiveness of Present Sampling Procedures . 19

3. DEVELOPMENT OF PROCEDURES . 23

4. PROCEDURES USED AT NBS 31

Apparatus .................. 31

Reagents for Basic Procedure ......... 32

Basic Procedures (for High-Grade Ores

and Concentrates). 34

Alternate Procedure Using Thioacetamide ... 46

Modification for Portuguese Concentrate

(about 10 percent Uranium) . 48

Modification for Refined Orange Oxide .... 49

Modification for Solutions Containing about

10 mg of Uranium 51

5. SUMMARY 55

6. APPENDIXES ..... 56

Appendix A. Details of INX Studies 56

Appendix B. Grand Junction Uranium Concentrate Standards Program of 1958 . 58

Appendix C. Summary of Drying Tests on IMCC

Material at NBS 8l

v
CONTENTS (Con't)

PAGE

Appendix D. Summary of NBS Drying Studies of

Four Lots of Blockson Uranium

Concentrates 87

7. ACKNOWLEDGMENT 93

8. REFERENCES 94

LIST OF TABLES

TABLE NO.

1. Contrast of "between bottle" and "within

bottle" agreement , as shown by NBS individual

assay results, for six bottles of two INX

lots sealed 2-6-57 11

2. Inter lab oratory disagreement of assay results

for 12 INX lots bottled between September

1956 and March 1957 12

3. Comparison of NBS individual assay values for

thirty lots of three types of Colorado Plateau

uranium concentrates (July - August 1963) . . 27

(Appendix B)

1. NBS initial .results for standard concentrate

"D", Bottles I and II (sampled in helium on

7-21; titrated on 7-30-58) 66

2. NBS initial results for standard concentrate

"D", Bottles III and IV (sampled in dry air on

9-5; titrated on 9-12-58) 67

3. NBS initial results for standard concentrate

"E" (sampled in dry air on 8-8; titrated on

8-15-58) 68

4. NBS initial results for standard concentrate

"F" (sampled in dry air on 8-20; titrated on 8-28-58) 69

5. NBS recheck and initial average results ... 70

vi
CONTENTS (Con't)

(Appendix B; Youden) PAGE

1. Statistical analysis of ranges for 45 sets

of four determinations (for three samples,

by three methods of base line establishment,

in five laboratories) 75

2. Averages of the 45 sets of four determinations; deviations from inter laboratory

averages ; and laboratory average discrepancy . 77

(Appendix D)

1. Changes in weight of Blockson samples during

heating at 110 °C in varied atmospheres, and

during storage 91

LIST OF FIGURES

FIGURE NO.

1. Change in weight of INX samples and/or caps

during storage in a humid atmosphere (about

0.012 g H

2 0/g dry air) 14

2. Change in weight of INX samples and/or caps

during storage in a dry atmosphere (over

Anhydrone) . ........... 15

3. Change in weight of separate components of INX bottle caps during storage in a dry

atmosphere (over Anhydrone) 16

4. Relative laboratory positions and average

differences from overall averages for three

years 21

5. Deviations from average U^Oo, for two

reference materials in 19fe-64 22

(Appendix Bj Youden)

1. Graphical diagnosis showing groupings of

deviations by laboratories . 78

(Appendix C)

1. NBS results for drying IMCC material in room air 82

vii
CONTENTS (Con't)

FIGURE NO. PAGE

(Appendix C)

2. NBS results for drying pre-treated IMCC

material in "dry" air 83

3. NBS results for heating pre-treated IMCC

material in humid air (about 0.013 g H^O/g

dry air 85

I

viii
STANDARD REFERENCE MATERIALS:

ANALYSIS OF URANIUM CONCENTRATES AT THE NATIONAL BUREAU OF STANDARDS

M. S. Richmond

Institute for Materials Research

National Bureau of Standards

ABSTRACT

NBS experiences with the problems of assaying uranium

concentrates are described. Umpire determinations of

uranium were performed on several thousands of ore concentrates from world-wide sources. Contributions were made

to the resolution of the sampling base line problem. Also,

it was demonstrated that the standard U-^Og, NBS No. 950a,

provides the over-all standard necessary for precise assay

of uranium materials. A comprehensive analytical procedure

applicable to all types of uranium concentrates is presented.

Key words: analytical procedure, assay, ore concentrates,

sampling base line, standard U^Og, umpire determinations,

uranium concentrates.

1
1 . INTRODUCTION

The development of atomic energy for military purposes

opened a new era in the analysis of uranium materials. In a general history of the development of the first atomic bomb,

Smyth [l] has noted the analytical contributions between

1939-42 by C. J. Rodden and others at the National Bureau of

Standards. By 19^3 j this Bureau had established a separate

section headed by Rodden to handle uranium analytical problems.

The section rapidly expanded to a level of about 20 employees

concentrating on development and control activities through

the war years

.

The breakdown in 19^6 of international negotiations for

the control of atomic weapons was followed by a renewed urgent

military demand for uranium. Between 19^9 and 1959 "the expenditures of the U. S. Atomic Energy Commission for the production

of uranium concentrates increased some 30-fold to more than

$600 million per year.

As the AEC sought production from every available source s domestic and foreign, there was a rapidly expanding analytical

load. However s most commercial and industrial laboratories

had little experience in analyzing uranium materials s and many

of the analytical methods developed or improved during the war

were classified or not available for publication. This situation led to the establishment of new AEC laboratories including the New Brunswick Laboratory (NBL) at New Brunswick, N. J. NBL was to carry on the control activities and special problems

2

I
that Rodden's group had handled at NBS; consequently most of

that group transferred to the AEC when NBL opened in April 19^9.

However , uranium procurement was still largely from foreign

sources , and the foreign contracts with AEC provided for umpire

determinations to be mad-:: at NBS. At the request of the AEC., this Bureau has continued both foreign and domestic umpii e work

through June J>0 9 1965. NBS has also conducted special studies

leading to a better understanding and control of some of the

sampling and analysis problems of uranium concentrates.

The foreign phase of the umpire work has involved laboratories representing Belgian,, South African, Canadian, Australian, or Portuguese producers and one or more of the U. S. A.E.C. laboratories at Fernald ( NLO ) , Weldon Spring (MCW),

Paducah (GCD) 3 or New Brunswick (NBL).* The domestic work

mainly involved 22 Colorado Plateau producers and the AEC

laboratories at Grand Junction (LPI) and Weldon Spring (MCW)

NLO's direct connection with the domestic uranium umpire work

was limited to a few samples of by-product concentrates derived

from phosphate materials and sampled at Fernald. Altogether,

NBS was called upon to assay concentrates from more than 50

different mills including about 29 in the western United States

and 14 in Canada.

Except for NBL, the abbreviation identifies the contractor

operating the laboratory, as follows: (NLO) National Lead

Company of Ohio, (MCW) Mallinckrodt Chemical Works, (GCD)

General Chemical Division of Allied Chemical, and (LPI)

Lucius Pitkin, Inc.

3
Each lot of concentrate was officially weighed and sampled

at one of the central processing facilities. The official

samples, representing a lot weight of 4,000 to 60,000 pounds, were assayed for uranium by the AEC (at the processing facility)

and by the seller (at his mill, usually). If the two assays

agreed with the preset splitting limit , the average of the two assays was the basis of settlement. The splitting limit

was 0.3 percent U-^Og, or more, In the early fifties, but has

been reduced to 0.2 percent b\^0g in recent contracts. When

the splitting limit was exceeded, a reserved sample was sent

to NBS for umpire analysis. This generally occurred in the case of 10 to 20 percent of the lots, but in 1953-54 serious

difficulties in the analysis of South African concentrates

resulted in the majority of the purchased lots requiring

umpire analysis.

During fiscal years 1953~57.> "the number of umpire requests

ranged between 170 and 300 per year. The later rapid development of new sources of uranium production led to about 500

umpire requests in fiscal year 1958j and 900 in 1959. AEC

procurement of uranium reached a peak of around 35 .5 000 tons of

U-^Og in fiscal year i960, but by then the major sampling problem

had been solved and the requests for umpire analyses had dropped

back to about 500 per year.

The splitting limit is the maximum allowable difference be- tween two assays.
Now the need for an uranium umpire program at NBS is

obviated. Sampling and assay problems are better understood,

generally reliable sampling procedures have been developed,

the black oxide standard reference material, NBS No. 950a,

has been accepted as a satisfactory uranium assay standard,

and the AEC 1 s foreign contracts are nearing expiration.

Consequently a close-out of the program is underway, and this

publication has been prepared to set down a comprehensive and

detailed account of the program at NBS as a guide for the use

of future umpires and other groups analyzing uranium.
2. THE PROBLEM OF SAMPLING WEIGHT BASE LINE

A. Basis of Choice

The primary problem in the assay of uranium concentrates

was the establishment of a reliable sampling weight base line.

The normal commercial practice of drying to constant weight is

very unsatisfactory for the complex salts in uranium chemical

concentrates. These materials usually contain 40 to 80 percent

uranium, and assorted impurities , Including vanadium, iron,

arsenic, molybdenum, copper, and thorium in varying amounts. They may also contain considerable amounts of ammonia, magnesium, sodium, calcium, sulfate, phosphate, and/or halogens,

depending on the production process. The impurities differ

not only from mill to mill but from time to time at a given

mill, e.g., lot moisture may range from 0.00$ to 10$, sodium

from 0.1 to 9% } and sulfate from 0.1 to 13$. For these hydrated concentrates, the so-called "dryingto-constant-weight" basis actually varies according to the

moisture content of the ambient atmospheres under which measurements are made. At NBS the moisture content of laboratory at- mosphere ranges widely, e.g., between 0.002 and 0.010 g HgO/g

dry air in November 1953 and between 0.008 and 0.018 in August

1953. Equally large variations probably occur at Fernald,

Weldon Spring, New Brunswick, South Africa, and at some of the

mills in the western United States. At Grand Junction, on the

other hand, the normally dry atmosphere shows relatively little

variation. Since contract settlements depended on the agreement

6
of assays performed under these variable conditions, there was

a need for a sampling procedure that did not require drying

to constant weight.

B. Historical Review . The existence of a drying problem was noted in 1950 in

connection with an African concentrate known as MgX, containing about 30 percent uranium; NBL observed that results for

"loss -on-drying" were more constant when obtained in a constant

humidity room instead of the usual laboratory, and also that

dried MgX seemed to pick up water from desiccants other than

magnesium perchlorate. However, the full scope of the problem

was not recognized for several years.

The extent of the correlation between assay results and

laboratory atmospheric conditions was most readily apparent

to the umpire. 'Each AEC (processing plant) laboratory handled

only certain types of materials, assayed large numbers of samples, and tended to assay samples soon after their preparation

and with the minimum of natural climate variation. On the

other hand, the umpire performed relatively few assays, received

samples from all problem areas, and performed its analyses from

weeks to months after the bottling of the samples.

By 1951 NBS was correlating the erratic interlaboratory

biases reported by AEC statisticians with probable differences

in laboratory atmospheric conditions. Producers, vendors, and

samplers were still prone to attribute interlaboratory disagreements to assaying or sampling practices of "the other
party," and. to propose evaluation of assay comparisons "by means

of standard, samples of uranium concentrates. NBS, however,,

emphasized that the specification of drying conditions was a primary problem that must be solved before the standard samples

could be established. In 1951 NBS studied the effect of "dry"

air (passed over indicating silica gel) on the rate and extent

of loss at 110 °C for MgX material. The loss values were increased as much as two percent of the sample weight when the

ambient air in the oven was replaced with drier air. Also,

reproducibility was much better and the time required for

reaching relative equilibrium was reduced from a highly variable

number of days to one overnight drying interval „ The dry-air

basis seemed adequate for interlab oratory assay comparisons

,

but the sampling plants wanted an easier way of getting the

official lot weight on the same basis as the assay samples.

In 1953 T. W. Steele of the Government Metallurgical

Laboratory In Johannesburg, South Africa, investigated the

effect of calcining temperature on the stability of uranium

precipitates and explained the results in terms of the hygroscopic nature of U0^ formed when the bulk product was calcined

in trays at 500 °C [2]. Subsequently, Calcined Products

(Pty.) Ltd. handled the drying problem by splitting a portion

from the 500-°C-calcined, bulk sample; further calcining the

split portion to 900 °C; and having all assays made on the

900 °C-calcined portion.

8
In 1952 NBL and NLO had begun investigating the use of a mixer -blender for preparing official samples of MgX material.

Their studies indicated that the blended material might be

bottled, sealed, and stored without changing in assay, and by

195^ NLO was blending entire lots and packaging samples for

assay on an "as is" basis. Rodden [3] reported at Geneva in

1955 that the mixer-blender method had "been used with some success". However, subsequent experience showed that the

base line weight difficulties were far from ended.

With increasing use of the blender method, bottle sealing

troubles became evident. Several years elapsed before the

closure problem was resolved and satisfactory sealing procedures were established. In the meantime, NLO intensively

investigated the drying behavior of a wide variety of con- centrates to determine the minimum amount of control required

to yield reproducible moisture-loss values. Some of the NLO

results have been published by Valent and Gessiness [4],

C. NBS Studies . Between 1956 and 1959.? NBS investigated the sampling

base line problem from three directions. The study of the

closure problem for INX material (an African concentrate

assayed on the "as is" basis) is described below with additional details in Appendix A. The inter laboratory standards program of 1958* coordinated by the AEC Grand Junction Office, is

described in Appendix B. The special drying studies of a few

790-939 0-65—

2

9
samples of two domestic by-product materials,, IMCC uranous fluoride concentrate and Blockson phosphate 5 are summarized

below and briefly described in Appendixes C and D. The IKK material containing about 60 percent uranium and

10 percent water^ was packaged in 30- to 40-g units in con- ventional glass bottles closed with hard plastic screw caps

and plastic tape covered with sealing wax. The analyst received

triplicate units from a lot and was requested to remove the

so-called "seal", immediately weigh the sample 5 dissolve the

entire sample and analyze an aliquot. However, at NBS 1- to 2-g samples from each of two bottles were analyzed and, if the

results agreed within 0.2 percent,, the third bottle was reserved

unopened. Assay agreement was satisfactory within bottles 9 but

often poor between bottles as illustrated in table 1, and very

bad between laboratories as illustrated in table 2. NBS aver- aged 0.70 percent U-^Og higher than the AEC values for the 12

lots listed in table 2. INX material appeared to be finer than 200 mesh; but the

vendor stated there was significant agglomeration due to the

high moisture content 3 and found up to twice as much moisture

in coarse agglomerates as in the finer portion. The vendor

insisted the assay disagreement was a segregation problem and

complained because NBS continued to use 1- to 2-g samples. How- ever } NBS had checked its results with enough 10-g samples to

International Minerals and Chemical Corporation.

10
Table 1. Contrast of "between bottle" and "within bottle"

agreement., as shown by NBS individual assay results.,

for six bottles of two INX lots sealed 2-6-57.

Bottle Storage Sample Percent U^ Og

NBS Months Date Weight Aliq.

No. Stored Opened (g) No

.

Assay Difference

O—J\ -AJ— *+—£-2 l 48 a

3_ 64 42 0 00

2 (64>8) c

( !o6)

1.59 1 64.42 . 00

6-Bd 3~ 1.53

a

1 64.93 .51

2 (64.99) ( .57)

1.52 J 1 O4.9O .50

6-Cd

4 6-4 1.50^f 1 64.75 .33

-1 )l '"7 D 3 g 1.47 1 o4.7o .34

7 A J— 1 R1 a

-L. 2-1- J- UU . U ( n no

2 (66.70) ( .03)

-1 )i pb 1.4o 1 oo . 05 — . 02

7-B 3- 4-25 1.47a1 66.21 - .46

2 (66.27) (- .40)

1.6lb ' e 1 66.26 - .41

7-C 4 6-4 1.51a ^

1 66.47 - .20

1.52° 5S 1 66.41 - .26

aAnalyzed by chemist H except for reduction and titration by

chemist R. ^Analyzed by chemist R.

c Parentheses indicate values not corrected for minor volume

changes (~0.05 ml).

dVery poorly sealed; the tape was not smooth and only partially

covered by wax.

eHad extra treatment with cupferron.

fHad extra treatment with HF. gHad extra treatment with HF 5 cupferron,, and HCIO^.

11
Table 2. Interlabor atory disagreement of assay results for

12 INX lots bottled between September 1956 and

March 1957.

Storage of NBS Bottles Percent U,0.

TY!"D O Date Monins "Ho uaxe+ Q As say Difference irom AJio ^ No. Sealed Stored Opened AEC Vendor NBS Accepted

1 9-29 5+ 5-4 71.29c -0.55 0.41 0.00

2 10-1 5+ 5-4 71.45 - .45 .44 .00

5 11-28 5- 4-25 62.44 + z^L .82 .55

h P R ^,j~ iiM-— pro OU , O.L + .60 A7

D

P£-— R_J J— 4_ PR fi"2

) nn + .79 .68 68

o PCL — 6U il PR » fC^ op Q"l

. y± + .40 .80 4n

4 6-4 » 7 2-6 5- 4-25 | 65.48 +1.42 .96 .96

4 6-4 ' 8 2-7 5- 4-25 69.51 - .56 .71 .00

9 5-1 5 6-4 71.87 -r± . O^ 1.16

10 5-1 5 6-4 72.26 +5.10 .74 .74

11 5-1 2- 4-26 70.14 + .64 .50 .50

12 5-4 5 6-4 70.51 -1.10 .69 .00

Aver age 5+ +0.59 +0.70 +0.45

Includes storage by AEC before exchange of AEC-vendor results.,

plus storage by NBS due to a backlog of work. AEC assays (at

the sampling plant) normally were made a day or two after

sealing; and vendor assays, some days or weeks later.

b The contract specified acceptance of the middle assay value

for umpired samples.

c Underlined values were accepted.

12
be convinced that segregation was not the major problem, and was investigating the dependability of bottle closures. By March

1957 NBS demonstrated there could be a significant exchange of

moisture between the sample and the bottle caps, especially

those containing paper sub-liners.

As detailed in Appendix A, six bottles were marked and

carefully cleaned (inside and/or outside as appropriate) before

their base weights were obtained. The controls (No. 1 and 2)

had been emptied of sample and were kept loosely-closed except

during extra weighings of bottles and caps. Bottles No. 3j 4,

5, and 6 each contained INK material and were left closed as received. Bottles No. 1, 3 3 and 5 were stored over "saturated

NH^NO-j" in a closed container , and bottles No. 2, 4 , and 6 were stored in a desiccator freshly charged with Anhydrone at the start of the experiment.

Observed weight changes are summarized in figures 1 and 2. The results for the loosely-closed, empty bottles, No. 1 and 2,

indicated that (1) within three months a dry cap could absorb

at least 0„35 g of water from the moist atmosphere in equilibrium with 40 g of INX material, (2) the absorption by the cap

continued for months but at a gradually decreasing rate, and

(3) the initial rate of this change could be great enough to cause significant assay differences even within the first two

days after the sample was bottled.

*The atmosphere in equilibrium with saturated ML,NCu at 25°C

contains about 0.012g Hp O/g dry air (equivalent to^60% relative

humidity at 25°C). d 13
i

1 1 1 1 1 1 1 r

Figure 1. Change in weight of INX samples and/or caps . during storage in a humid atmosphere (about

0.012 g H

2 0/g dry air).

The caps were made of hard black plastic and lined with

plastic or metal foil. The relative tendency of the different

parts of the taped and waxed cap to lose moisture is indicated

in figure 3. Variations in closure quality were observed also,, as follows: (1) there were differences in the extent to which

the plastic tape around the cap was covered with sealing wax^

(2) when the bottles were first opened^ the caps usually were

14
Figure 2. Change in weight of INX samples and/or caps

during storage in a dry atmosphere (over

Anhydrone)

easy to turn; (3) cap liners for a single lot were not identical (e.g., some were covered with metal foil and some with

plastic); and (4) a little sample material was often present

between the cap and the top of the bottle. The data in fig- ures 1 and 2 indicated that the rate of leakage from the

"sealed" bottles, No. 3, 5 3 4, and 6 was (1) different for

each bottle^ (2) relatively constant for a given bottle except

15
Figure 3. Change in weight of separate components of INX bottle caps during storage in a dry

atmosphere (over Anhydrone). (Base weights

were obtained on 6-26-57 > after separating

the parts and exposing them to room air

for two hours.)

during the initial weeks in the humid atmosphere (i.e., after

the taped and waxed cap was near equilibrium with the surrounding atmosphere); and (3) large enough to account for assay

differences up to 0.3 percent in four months.

Thus, it became apparent that the original "as is" INX material was losing varying amounts of moisture by diffusion

either past the closure, to the cap, or both. Since AEC assays were performed at the sampling plant, usually a day or two

after the bottles were sealed and probably before the vendor

received his samples, it was concluded that the AEC results

should most nearly represent the true assay of the gross lot.

16
On this basis , the accepted values for the 12 lots listed in

table 2 probably averaged 0.45 percent high. The +0.7 percent

average bias of NBS in table 2 was attributed to a combination

of the factors involved in the three-month average storage

time: the initial dryness of the caps, the quality of the

seals , and the storage conditions. The magnitude of the bias

was in line with the storage time, the experimental evidence

(see figures 1 and 2) that a dry cap could absorb water equivalent to an INX weight loss (or higher assay) of nearly one percent, and the evidence (see table 1 for results from duplicate

bottles with duplicate storage history) of 0.4 to 0.5 percent

U-^Og differences due to the different quality of seals.

The IMCC and Blockson concentrates presented more specialized aspects of the sampling base line problem. Although IMCC

material containing sulfate and/oi phosphate as well as fluoride, could be dried to a reproducible state at 110 °C in a controlled moist ambient atmosphere (equivalent to 60 percent

relative humidity at 80°F), this hygroscopic material gained

as fast as 0.3 percent per hour and up to a total of two or three percent, with subsequent loss of hydrogen fluoride during

storage or drying. For each of three umpired samples, four

laboratories agreed within 0.^0 percent on the "as is" basis,

but one of the laboratories was about one percent high on the

dry basis, presumably due to faulty storage or drying (i.e.,

the laboratory did more than remove the moisture absorbed after

the sampling plant dry weight basis was established). NBS

drying tests on IMCC material are described in Appendix C. 17
Two lots of Blockson material gained up to two percent

during ordinary f

' drying" and lost up to one percent when heated

to the same temperature in bone-dry air. The special drying

procedure and additional details of the tests on Blockson

material are given in Appendix D.

D. Resolving the Base Line Problem. The breakthrough on the closure problem began in 1956

when Lucium Pitkin, Inc., used Mason jars for bottling Anaconda

material in Grand Junction. The Mason jar lids were not lined

and had a thin rubber gasket that gave a good seal and thus

permitted assay on the "as is" basis.

Grand Junction continued to use the so-called "dried-toconstant-weight" basis until late 1959 ^ but actually this was more of a "vacuum canned" basis because material dried at 110 °C and immediately put into warm sample bottles in the dry,

low-pressure atmosphere of Grand Junction tended to be vacuum

sealed on cooling to room temperature. When such samples were heated at 110 °C at NBS they usually gained instead of losing;

any gain was reported as "0.00$ loss".? and thus made the "dry

basis" equal to the "as is" basis „ NBS early noticed that many

of the Grand Junction samples were received under vacuum and

that on such samples good assay agreement with Grand Junction

was obtained on the "as is" basis.

By the fall of 1958, after initiation of the interlaboratory standards program described in Appendix B, the Grand

Junction sampling plant was deliberately "vacuum canning" its

18
samples. The laboratory samples were put in ""baby food 1

' bottles

of the press-on type; all bottles were put in the oven together

for a final drying and then rapidly capped and sealed while

still hot [4-b], Also, it had become standard practice at NBS

to take all assay samples of Western materials immediately

after the sample bottle was first opened „ As might be expected,

no loss -on- drying was found unless the vacuum seal had been

broken prior to sampling,, Furthermore, NBS "as is n results

agreed well with Grand Junction results , indicating: (1) the

adequacy of the assay procedures , (2) the absence of storage

and moisture factors in the Grand Junction analysis , and (3) the

effectiveness of "vacuum canning" in avoiding changes due to storage conditions. Finally in late 1959 Grand Junction, with

the support of NBS, eliminated the laboratory-moisture determination for Western concentrates and officially adopted the

present practice of hermetically sealing analytical samples

at the same time, and under the same atmospheric conditions as those under which, the sampling plant performs the moisture

determination . E. Effectiveness of Present Sampling Procedures

An evaluation of several sealing methods at MCW has been

described by Nelson, Kneip, and Mohl [5]. Since I960, the

effectiveness of uranium sampling procedures has also been

checked by means of the AEC General Analytical Evaluation

Program. This program, coordinated by the u. S. AEC ' s New

Brunswick Laboratory, and designed to permit the various

19
laboratories performing analyses for the Commission to evaluate

their performance, was extended to uranium concentrates after

the establishment of the hermetic-seal bottling method. From

196l to 196k } the program dealt with four types of concentrates

each year. A reference or "known" sample was prepared for each

of these concentrates. Once a month each cooperating laboratory received four samples , in any combination of materials

,

both production and disguised reference samples, so that at the

end of the year there were 12 results from each laboratory on each of the 4 materials. Six of the results were on the monthly production lot samples and six on the reference samples.

The only analysis made was the U^Og assay on an "as received"

basis. The gross weight of each sample was noted at the time

of bottling and again at the time of analysis; if leakage had

occurred that bottle was omitted from the study.

All results have been evaluated in annual reports by

Roszkowski, Mullin, and Lanza [6], Although true uranium values

are not known for the reference materials, the results have

disclosed significant differences among the laboratory averages

each year, and the presence of statistically significant changes

in laboratory relationships during the first two years. There

was decided improvement in laboratory agreement for the third

year over that of the first two years, as shown in figure 4. Interlaboratory agreement has shown little if any relation to the particular uranium concentrate analyzed; usually, if a

20
+0.07

+0.06 -

+0.0S

+o.oU

+0.03 +0.02

+0.01

0 -0.01

-0.02

-0.03 -O.OU -o.o£

-0.06

-0.07

GCD

'

LPI' \ LPI

NBS \ ^\ MOW

MCW*' \

\ /

\ / NBL

NBL 1

8/60-7/61 9/61-8/62 9/62-8/63 Year

Figure 4. Relative laboratory positions and average

differences from overall averages for

three years. See [6], NBL-203, p. 9.

laboratory showed a bias on one material., it showed a similar

bias on other materials.

Although the reproducibility between bottles of a material

has been generally good, there was a large difference in reproducibility for two reference materials studied in 1964 „ This

is shown in figure 5, where each point represents the assay of

one bottle of material „ For the Climax materials the inner s solid lines represent 95 percent confidence limits for the

21
.20 _

CLIMAX SAMPLES

*

i " B "* "

m 0

•

• • • " . • • •

-.10

* — • • • • . • •

• • • _

-.20

1 1 -

.30 NBL MCW GCD LPI NBS

• • DAWN SAMPLES * _

20

• •

• _

• -

.10 •

0

• • ' _

• -

*

•

-.20 - • • • -

-.30 1 •

l< ' 1 1 " 1'

1 1 II 1 1 1 1 1 1 1 1 1 SDMJ SDMJ SDMJ SDMJ SDMJ

Figure 5. Deviations from average U^Ooj, for two reference

materials in 1963-64. p See [6], NBL-221, pp. 28, 31.

laboratory averages 3 and the outer s dashed lines represent 95

percent confidence limits for a single plotted point. Bottling

reliability has been greatly improved since the 1950' s, but the

variability of the Dawn reference material indicates that un- suspected sampling variations may still occur. This emphasizes

the continued need for basing assay evaluations on a standard

of known composition, such as NBS No. 950a. The effect of

variations in composition on the assay can still be determined

by adding approximate amounts of appropriate impurities to known

amounts of uranium

,

22
3. DEVELOPMENT OF PROCEDURES

As the umpire , NBS has received a wide variety of samples

from more than 50 producers , but only spotty knowledge of the sources, production methods, and total composition of individual samples. Consequently, the assay method was chosen for

its general applicability to accurately assaying relatively

small numbers of samples originating from a variety of materials. This eliminated the need for varying the method with

type of concentrate. One basic procedure was used for all

uranium umpire samples except for a few that were either of

low uranium content or of refinery grade. The basic procedure

was designed for materials containing at least 50 percent ura- nium and having a splitting limit of 0.2 percent. It is

completed with a titration of 100 to 320 mg of uranium and is

described in detail in section 4. That section also includes

a brief description of three modified procedures indicating

the changes made to obtain higher accuracy, remove larger

amounts of interferences, or determine uranium in the 10-mg

range

In the umpire method, the uranium is dissolved by treatment with mixed acids--generally nitric, hydrofluoric, and

sulfuric. The hydrogen sulfide group is removed by precipitation in a diluted sulfuric acid solution (5:95). Additional

interferences are removed by oxidizing the filtrate, increasing its acidity (to 1'9) , treating with cupferron, and

23
extracting with chloroform. Most organic matter is destroyed

by fuming with nitric acid. Residual organic matter and nitric

acid is removed by additional fumings with perchloric and sulfuric acids. The solution or a suitable aliquot is reduced in

a Jones reductor containing zinc amalgamated with 10 percent

by weight of mercury, and then aerated to oxidize U(III) to U(IV). Excess ferric solution is added to completely oxidize

the uranium, phosphoric acid is added to complex the remaining

ferric iron, and the ferrous iron resulting from oxidation of

U(IV) to U(VT) is titrated visually with potassium dichromate

solution that has been standardized against a standard sample

of uranium oxide (U^Og).

This general method has been used for umpire uranium

assays since the mid-forties. The chloroform extraction of

cupferrates was reviewed by Furman, Mason, and Pekola [7].

The "lO-percent-amalgam" reductor recommended by Grimaldi [8]

for elimination of nickel interference was adopted for general

use at NBS because of its stability (long life). The excellent

study by Sill and Peterson [9] of a different uranium assay

method provided valuable information about the analytical

chemistry of uranium 0 Methods used for uranium assays in

other laboratories have been reviewed by Rodden [3,10] and

Steele and Taverner [11]. The recent review by Booman and

Rein [12] is of a more general nature. The compilation by

Jones [13] of selected measurement methods for product materials give details of several sampling and assay procedures

24
that also apply to source materials.

In South Africa much use has been made of the cellulose

column method; and in the United States, MCW [14] prefers to separate uranium from impurities by means of the tetrasodium

salt of ethylene-diamine-tetraacetic acid (EDTA) and ammonium

uranyl phosphate, reduce uranium in a lead reductor, and titrate with eerie sulfate. LPI, NBL, NLO, and GCD have used

methods similar to those of NBS but varying in regard to the

thioacetamide use, HCl-HBr removal of arsenic, cupferron

extraction techniques, percent mercury in the Jones reductor,

etc

At NBS it has generally been more convenient to make the

sulfide separation by use of hydrogen sulfide than by thioacetamide. The latter has been used successfully, however, as described in the alternate procedure based on the LPI procedure [15] and included in section The analytical chemistry

of thioacetamide has been reviewed by Swift and Anson [16],

We have deliberately avoided use of hydrobromic acid for

volatilizing arsenic because the presence of hydrogen bromide

in our laboratory appeared to cause some low results and

because we failed to obtain proof that it was necessary. Rowe

[17] also found no serious interference by arsenate in the

volumetric determination of uranium, but his experimental con- ditions and requirements were somewhat different from those of

the umpire method.

790-939 0-65—

25
The precision of the basic procedure was demonstrated in

1958 in the standards program described in Appendix B. That

program excluded operator differences at NBS, whereas the GAE

program (section 2.E) does not. In I963 an additional study

was made of the precision of umpire assays. Thirty samples

selected by the AEC were analyzed as routine umpires except

that a second (i.e., extra) aliquot was titrated for most of

the solutions. The analyses were performed by three analysts s and all used the same pipette , same dichromate solution, same titer, and same correction for loss in extraction. Except for

two lots (No. 25 and 26 ) s one analyst prepared one sample

solution and assayed the first aliquot of it; another analyst

did likewise with a second sample. Immediately after the

first aliquot was removed by one analyst 3 a different analyst

removed and assayed a second aliquot. Two aliquots each of

57 sample solutions and 15 solutions of NBS Standard No. 950a

were assayed. The 15 first aliquots of standard solutions had

a range of 0.11 and an estimated standard deviation of 0.03.

All sample results are listed in table 3. For 12 of the 30

samples , the difference between first aliquots of two solutions

exceeded 0.06 and ranged up to 0.l4. Although only one sample

in this study gave a difference greater than 0.03 between the

average of two (first) aliquots and the average of four (first

and second) aliquots s it was made a standard practice at NBS

after September 1963 to titrate second aliquots of any

26
Table 3. Comparison of NBS individual assay values for thirty lots

of three types of Colorado Plateau uranium concentrates

(July - August 1963)

Lot Individual Results (Percent UqQq) NBS 1st Aliquots 2nd Aliquots

No. Soln. 1 Soln. 2 Soln. 1 Soln. 2

Differences

of 1st Gr. Ave Aliquots -1st Ave 79.86-B 79.97-B 81.28-B

81.09-B 81.15-B

79.88-S

79.97-S 81.33-S

81.17- S 81.18- S

79.90-S 80.07-S

81.31-S 81.18-P 81.19- P

79.90-B 79.95-B 81.35-B

81.18-B 81.15-P

0.02

.00

.05

.08 .03

+ 0.01 + .02

,02 ,0301

6

78

910

81.77-B

81.55-B 86.87-B

83.70-P 82.11-B

81.78-S

81.66-S 86.90-S

83.71-S 82.00-P

81.75-P

81.64-P 87.02-P

83.78-S

82.17-S

81.56-P

86.95-P

83.71-P

82.03-B

.01

.11 .03

.01

.11

.01 .00

.06

.02 .02 11

121314

15

85.98-B 84.83-B

85.75-B

86.09-B

85.98-B

85.87-S 84.70-S

85.78-S

86.10-S

86.06-S

85.99-P

84.75-P

85.97-P

85.87-B

84.78-P

85.81-P

86.15-P

86.07-P

.11 .13 .03

.01

.08

.01 .00

.02

.01 .00 16

1718

1920

85.45-B

85.59-P 85.42-P

85.68-P

85.14-P

85.41-S 85.66-S

85.56-S

85.72-S

85.14-S

85.65-S 85.54-S

85.68-S 85.15-S

85.42-P

85.58-P

85.56-P

85-.64-P 85.18-P

+ .04

- .07

- .14

- .04 .00

.00

.00

.03

.02 .01 21

2223

2425

85.12-P

85.94-P

86.27-P

85.59-P

86.03-S

85.14-S

85.87-S 86.23-S

85.52-S

86.01-S

85.07-B

85.89-B 86.24-B

85.60-S 85.98-B

85.19-B

85.86-B 86.23-B

85.53-B

86.01-B

- .02 + .07 + .04 + .07 + .02

.00

- .01

- .01 .00

- .01 26

27 87.05-B

86.46-B 87.00-B

(86.14)-s' 86.54-S

87.07-S 87.00-P

86.44-S (86.21)P 86.57-B

.05

.08

.01 .00

2829

30

86.90-B

86.50-B 84.19-B

86.83-S 86.48-S

84.25-S

86.86-S

86.50-S

84.25-S

86.84-B

86.44-B

84.22-B

.07

.02 .06

.00

.01

.01 Letters (B, S, and P) identify the three analysts.

5 This value is listed because the analyst had no explanation, but it is omitted from the average because it has been a practice at this laboratory to discard such values. 27
duplicate umpire samples that differ by more than 0.06 percent

U^Og for the first aliquot s. This now occurs on less than

10 percent of the samples. For accurate results, it is necessary that: (1) the material be weighed on the "as-bottled" basis, (2) refractory

uranium materials (including U02

) not escape dissolution by

floating above the area of reaction, (5) uranium be completely

washed from the sulfide filter , (4) the diluted uranium solution

be well-mixed before cupferron is added to it, (5) physical

losses in extraction and aeration be corrected for, (6) cracked

fuming flasks be promptly recognized and eliminated, and (7)

volumetric calibrations and temperature differences be suitably corrected for. Of the listed sources of error, all ex- cept the first and sixth are easily checked by carrying standard U-^Og through one or more steps of the procedure. The

possibility of over-looking a human measurement error is

greatly minimized by assaying two separate and different

weight portions of each sample.

The length of the procedure provides many opportunities

for error, but those encountered most often are loss of uranium

or incorrect physical measurements. In trying to insure recognition of any errors, we have deliberately aimed to keep errors

in one direction, to minimize compensating errors. Thus, we chose to extract with a relatively large, but constant, number

of portions of cupferron-chloroform (aiming to insure complete

28
removal of extractable interferences and limit the extraction

error to a loss of uranium in spray) . The average loss is

determined by similar extraction of known solutions s and assay

results are corrected accordingly. The magnitude and reproducibility of this loss from known solutions provide one valid

test of an analyst's ability to perform umpire analyses.

The rate at which aeration oxidizes uranium beyond the

tetravalent state has not been significant in assays to 1 part

in 1^000 of solutions containing more than 100 mg of uranium

and no catalysts such as copper s molybdenum., or platinum. The

presence of catalysts can be detected by extra aeration of an otherwise duplicate aliquot. Doubling or tripling the aeration

time should have no effect except for the expected greater

physical loss in the air stream passed through the solution.

In the umpire procedure at NBS 3 this loss amounts to about

0.1 percent and is compensated for in the standardization

,

where the standard uranium solution is aerated the same as the

sample. In determining the composition of standards such as NBS No. 950a^ physical loss in aeration is either (1) greatly

reduced by washing the escaping air stream, or (2) avoided

by passing air over a moving solution.

In washing the reductor, introduction of large amounts of

air is avoided, but to minimize mixing of successive wash

portions, each wash portion is deliberately drained to the top

of the amalgam. Introduction of small amounts of air does no harm providing the final reduced solution contains excess U(III).

29
The, basic umpire procedure is used only for solutions containing at least 100 mg of uranium and this should give enough of

the visible olive color of U(III) to persist until the reduced

solution is mixed and ready for the aeration step. For less

than 100 mg of uranium^ the procedure is modified to control

aeration time more closely.

Over the years the assay procedure has been modified as needed to keep pace with increasing reliability of the bulk

sampling procedures. The present basic procedure has proved

satisfactory for concentrates with splitting limits of around

0.2 percent. However 3 if greater assay accuracy is desired., it

would be helpful to have a better understanding of the interplay of conditions such as incomplete separation of sulfides

(e.g. j arsenic and platinum groups) fuming temperatures and

reduction with "10-percent" amalgam; to know more about the

effect of vanadium and of permanganate on the cupferron extraction; and to correlate assay results with the qualitative com- position of the sample.

30
4. PROCEDURES USED AT NBS

A. Apparatus

1. Shaking heater . NBS uses custom-made assemblies

that have evolved from the suggestions of J. J. Tregoning and

A. Padgett of NBL in 1951. Six 550~w, 4. 8-inch-square heating

units (Precision type "HA") are mounted in a row on a base

sheet of 0.25-inch transite that oscillates approximately 1.5

inches 90 times a minute. The transite base is mounted on an angle iron frame provided with eight roller skate wheels which

roll .(four on a horizontal plane and four against two vertical

planes) on two fixed angle iron guides. The shaker is driven

by a 1750~rpm, 0.33-hp motor connected through a 30:1 gear

reducer to the drive shaft. A transite strip, 8.5 inches

wide, with a 4-inch-diameter hole over each heating unit is

mounted so as to prevent the flasks from sliding off during

shaking.

The latest NBS assembly has a transite apron in front and

on the level of the heating units 3 about three inches above

the transite base. A row of six receptacles is mounted on the

underside of the apron and 10 inches in front of the heating

units. The apron covers the wiring without stopping air circulation, provides a cooling area for sample flasks, and de- creases exposure of metal framework to acid. A variac for

each unit is mounted in front of and just below the shaking

assembly.

31
The Lowe Shaker Plate , a different assembly that is used

in several uranium assay laboratories, is semi-custom made by

Wesco Electric Company, 4ll Glenwood Avenue, Grand Junction,

Colorado.

2. Bubble dispersion tip . This is made by sealing a number of fine copper wires (of about 0.l8-mm diameter) radiating from a center in a definite pattern, between a cone formed on the end of a glass tube and a circular glass disk.

After the glass parts are sealed together and ground to expose

the ends of the wires, the wires are dissolved in warm nitric

acid. A detailed description of the tip and its construction

has been given by Branham and Sperling [18],

3. Titration illumination . During titration, the beaker

rests on a plate of flashed opal glass supported over a standard cool white fluorescent light. The glass is opal-flashed

only on the bottom surface.

B. Reagents for Basic Procedure

1. Standard potassium dichromate solution (0.027 N_: 1 ml of solution equivalent to 0.0058 g of U-^Og). Dissolve

23.0 g of potassium dichromate (A. R. , Primary Standard) in

17.2 liters of water. Standardize, as directed in section

C. 9 against the standard black oxide, No. 950a, used on the

basis of 99.9^ U3°8 wnen freshly ignited in an open crucible

at 900 °C for one hour.

2. Phosphoric-sulfuric acid mixture . Add 600 ml of

sulfuric acid (sp. gr . 1.84) to 1400 ml of phosphoric acid

32
(85$) and mix.

3. Indicator solution (0.01 M ). Dissolve 1.35 g of

sodium diphenylamine sulfonate in 500 ml of water.

4. Ferric chloride solution . Dissolve 60 g of FeCl^*

6E^0 in 1500 ml of water, filter through a coarse-porosity

sintered-glass filtering funnel. Add 15 ml of diluted sulfuric

acid (1:1) that has not been exposed to fumes of nitric acid.

Mix.

5. Cupferron solution . Dissolve 18 g of cupferron in

300 ml of ice-cold water.

6. Amalgamated zinc for 10$ Jones reductor . Dissolve

70.8 g of mercuric chloride in 1200 ml of hot diluted sulfuric

acid (1:99) and cool the solution to room temperature. Clean

5^0 g of 20-mesh zinc (low in As., Pb, and Fe) by covering with

diluted sulfuric acid (5:95)j stirring for about 10 seconds,

rapidly decanting and rinsing three times with approximately

300-ml portions of water. Immediately after decanting off the

last rinse, add the mercuric chloride solution and agitate the

zinc, as by shaking in a loosely-closed bottle, vigorously for

two minutes and occasionally for 10 minutes. Discard the

liquid by decantation. Wash the amalgam several times with

diluted sulfuric acid (5:95) and then several times with water.

Cover with water, stir about two hours after amalgamation to crush the lumps formed by the fresh amalgam, and allow to stand overnight. Prepare the reductor column (about 22 mm

inside diameter) by adding to the tube a plug of glass wool,

33
a little water and then about an inch of the amalgam at a time,

gently tamping it in place with a glass rod. Wash thoroughly

with diluted sulfuric acid (5:95) and with water.

C. Basic Procedure (for High-Grade Ores and Concentrates )

-L* Sampling . Mix the material by rotating and shaking

its container for several minutes. Carry out the appropriate

procedure described below, using the grab-sampling (see below)

method particularly for the materials to be reported on the

"as received" basis and for very hygroscopic concentrates. If

the gross weight of the bottled sample was noted on the bottle

at the sampling plant, reweigh shortly before sampling in the

laboratory, to determine if the "as received" basis has been

maintained. Grab a total of at least four samples (usually

1.5 g each) of each lot that is to be assayed on the "as received" basis. Take all samples from underneath the surface

material, and sample different regions whenever possible.

Make determinations in duplicate; if more than one bottle of

the material is submitted, assay one sample from each of two

bottles

(a) Grab-sampling . Immediately after breaking the

"seal" of the bottle, rapidly transfer two or more samples

from it to cap-style, 25 x 40-mm weighing bottles. Close each

weighing bottle promptly and firmly and weigh it (to 0.1 mg)

30 to 60 minutes later. Obtain the assay sample weight by

difference after pouring the sample into a narrow-mouth,

500-ml Erlenmeyer flask and weighing the emptied bottle.

34
Reserve the extra samples for assay rechecking as needed.

Store with a tare weighing bottle but without desiccant.

(b) Direct weighing . Transfer the sample to a tared

weighing pan and determine its weight, to the nearest 0.1 mg, 60 seconds after opening the container. Transfer the sample,

with the aid of a small brush, into a 500-ml Erlenmeyer flask.

(c) Samples for moisture . If the analysis is to be on the dry basis, take two additional samples, taking one just

before and one just after the assay samples. Transfer approximately 5 g of material to a weighed, tared, cap-style, 40 x 50-mm weighing bottle, close the weighing bottle promptly and

firmly, and weigh it 50 to 60 minutes later.

2. Moisture determination . Dry the moisture samples at 110 °C for approximately l6-hour intervals. Dry the materials

from different sampling plants or with widely different moisture contents separately. In general, do not dry over 12 portions together. During the first drying interval, leave the

weighing bottles wide open, with their tops lying next to them,

but during later intervals, leave the tops tilted on the

bottles in order that the latter may be closed as soon as possible after the oven is opened. Cool seven bottles over magnesium perchlorate in an 8-inch desiccator for one hour;

then open each bottle for an instant, close firmly, and leave

in the desiccator for at least one hour longer before weighing.

Check the weight of the tare bottle, which has been handled

exactly as the sample bottles, and then weigh the samples

35
against the tare. Dry every sample that is put in the oven together , until the weight of each is constant or increases

in the same interval but for not less than three intervals.

3. Dissolution . Proceed, as follows, with (a) or (b)

depending on sample size.

(a) Small assay sample (1.5 to 2.0 g) . Wash down

the inside of the flask with approximately 15 ml of water and

swirl to mix. Add 15 ml of diluted sulfuric acid (1:1) and

about 15 ml of diluted nitric acid (1:1); for pitchblende ores, increase the nitric acid to 50 ml (1:1) and also add 20 ml of

diluted hydrochloric acid (1:1). Digest at 80 to 100 °C until

reaction ceases (up to one hour), swirling as needed to keep

the sample dispersed. Wash down the wall with water and add

up to one ml of hydrofluoric acid (48$). Place the flask on

a fast heater and heat, while shaking the heater, until the

sulfuric acid refluxes at least one inch up the wall of the

flask; if hydrofluoric acid was added, continue heating until

the sulfuric acid refluxes nearly to the neck of the flask.

Remove from the heater; and when the flask is cool, wash down

the inside of the flask with 145 ml of water. Cover with a beaker and digest on a steam bath for one hour, swirling once near the middle of the digestion. Examine for complete decomposition; if a significant amount of dark material persists,

add one ml of perchloric acid, evaporate, refume, dilute, and

digest again. Continue as directed in section C.4.

56
(b) Large assay sample (8 g) . Wash down the inside

of the flask with 25 ml of water and swirl to mix. Add 25 ml

of concentrated nitric acid. Digest at 80 to 100 °C and swirl

occasionally until reaction ceases (up to one hour). Cool and

wash down. Cautiously add 35 nil of concentrated sulfuric acid

and mix. Add about 2 ml of hydrofluoric acid. Place the flask

on a fast heater and heat, while shaking the heater, until the

sulfuric acid refluxes nearly to the neck of the flask. Cool.

Cautiously add 200 ml (more for difficultly soluble material)

of water and mix. Cover and digest on a steam bath for 30

minutes. Cool to room temperature. Filter through an 11-cm

No. 40 paper into a 500-ml volumetric flask. Wash with 100 ml

of diluted sulfuric acid (2:98) and several times with water.

Ignite and weigh the residue, (If it amounts to 0.1 percent

of the sample, test the residue for uranium as directed in

section C.3c) Dilute the filtrate to nearly 500 ml while

mixing the solution by swirling. Cool it to room temperature.

Dilute the solution to the mark, mix thoroughly, note the

temperature and transfer a 100-ml aliquot to a 500-ml, narrow- mouth Erlenmeyer flask. Before diluting the aliquot, dry the

stopper and neck of the volumetric flask and close the flask

tightly so that a duplicate aliquot may be obtained later if

desired. Add 50 ml of water to the 100-ml aliquot. Continue

as directed in section C.4.

37
(c) Residue . When f luorimetric or spectrographic

checking of a residue is not convenient , analyze the residue

for uranium simply by decomposing it, usually with the aid of

hydrofluoric acid, and then proceeding as for a reagent blank,

section C.lOa.

k. Treatment with hydrogen sulfide , (Carry out the work

in an efficiently ventilated hood.) Heat the solution of the

sample, in 15 0 ml of diluted sulfuric acid (5*95) s "to boiling.

Immediately attach the flask by means of a short glass tube

in a rubber stopper to a hydrogen sulfide manifold. Connect

the last exit of the manifold through a trap to a regulator to maintain a pressure equivalent to 18 inches of water. Sweep

out the air in the flask by gassing one sample at a time and

loosening the stopper intermittently while vigorously and

constantly swirling the flask for two or three minutes. Then

tightly stopper the flask and repeat with successive solutions.

After connecting all flasks to the manifold, cool them to icebath temperature. Continue the gassing and occasional swirling

until the swirling does not noticeably decrease the pressure

in the ice-cold flask (usually at least one hour). Close the

hydrogen-sulf ide-f illed flasks while cold and let them stand

at room temperature overnight.

Although the gassing technique described above usually

insures the presence of excess hydrogen sulfide in each solution, pass hydrogen sulfide over the solutions again just

before filtration, while also saturating a wash solution of

38
diluted sulfuric acid (2:98) with the gas. Filter the sample

through a No. 40. Whatman paper into a nar row-mouth 9 lipped,

500-ml Erlenmeyer flask. Wash with at least 100 ml of the

hydrogen sulfide-sulfuric acid solution. Add 5 ml of diluted

sulfuric acid (1:1) and 10 to 20 glass beads to the filtrate.

Mix the solution and place the flask on a fast heater. Boil

until the volume is reduced to 75 to 80 ml.

5. Extraction of cupferrates . Heat the above solution,

containing 12 ml of concentrated sulfuric acid, to boiling

and add dropwise a 2-percent solution of potassium permanganate

until the uranium solution is pink. Cool the solution in an

ice bath to a temperature of 5 °C. Transfer the solution

quantitatively to a 300-ml separatory funnel containing a few

drops of chloroform; use water for washing the flask and

diluting the solution to 100 ml. Swirl to mix . If the pink

color has faded, add 1 or 2 drops of 2-percent potassium

permanganate to make it pink again.

Add 25 ml of an ice-cold, 6-percent cupferron solution,

mix by swirling the mixture for 5 seconds, and allow to stand

for a few moments. Add 25 ml of ice-cold chloroform and shake

vigorously for 15 seconds. Carefully release the pressure

through the stopcock. Each time the funnel is returned to the

upright position make sure that a drop of aqueous layer is not

trapped next to the stopcock. Then loosen the stopper and

wash it and the top of the funnel with a little chloroform.

39
Allow the funnel and contents to stand until the layers have

separated completely, but not long enough for the chloroform

layer to start bubbling and giving a curdy, light-colored precipitate. Drain off most of the chloroform layer and repeat

the extraction with chloroform.

Add permanganate to make the solution pink again. Add

10 ml more of cupferron solution and extract twice more with

25 -ml portions of chloroform.

Add another drop or two of permanganate , a third portion

of cupferron (usually 10 ml), and extract with three more 2 5 -ml

portions of chloroform. The third portion of cupferron should

give a white precipitate; its chloroform extract should be pale

blue-greenish with no brownish tinge even after short standing;

and the last chloroform layer should be colorless. Before

draining the last extract, wash the outside of the funnel stem

with chloroform. If colored extract has dried on the inside

of the stem, wash it out with diluted sulfuric acid; this usually

is necessary for the large stems (9 -mm inside diameter).

Drain the aqueous layer from the separatory funnel back

into the lipped, 500-ml Erlenmeyer flask, washing out the

separatory funnel at least three times with water. Add 15 ml

of concentrated nitric acid, 15 ml* of diluted sulfuric acid

(1:1), and swirl to mix.

*

If the solution contains less than 380 mg of U-zOg, omit

this sulfuric acid.

40
6. Fuming . Swirl again to mix well. Boil the solution

until sulfuric acid refluxes to the neck of the flask. After

the solution has cooled, wash down the inside of the flask

with at least 15 ml of water. Add 1 ml of perchloric acid

(70$). Again boil until the sulfuric acid refluxes into the

neck of the flask. Repeat the cooling, washing down, and

fuming, twice more. After the fourth fuming, cool the solution,

add about 100 ml of water, and heat to dissolve all soluble

salts. Wash down the inside of the flask immediately after

the last heating. After the solution has cooled, transfer it to a 200-ml volumetric flask* and dilute nearly to volume

while mixing by swirling. Allow the solution to come to room temperature.

7. Aliquot ing and reduction. Dilute the solution

exactly to the mark and mix thoroughly. Record the room

temperature. Remove a 50 -ml aliquot and transfer it to a 250-ml beaker; the aliquot should contain at least 100 mg of

uranium. Add 2-percent potassium permanganate, usually one

drop, until the uranium solution is pink. Heat the solution

just to boiling; then cool it, in a. water bath, to room temperature. Immediately before each group of reductions, wash

the reductor several times with diluted sulfuric acid (5r95) 3 then with water. Reduce an extra aliquot of the first sample;

If the solution contains less than 380 mg of U^On, do not

transfer it to a volumetric flask. Instead, adjust the

volume to 90 ml, oxidize with permanganate, heat to boiling,

cool, and reduce as in section C.7.

790-939 0-65— 4l 4 ^ ^
then reduce the test aliquots. Make each reduction by passing

through the reductor in the following order: about 20 ml of

diluted sulfuric acid (5:95)^ "the uranium solution, 110 ml of

diluted sulfuric acid (5:95) in three portions , and finally

110 ml of water in three portions. Carry out the reduction

in three to four minutes.

8. Aeration and titration . Transfer the reduced solution

to a 600-ml beaker. Aerate with a stream of fine bubbles of

washed air* for 15 minutes , adjusting the rate of aeration so

as to change the brownish solution into a clear green one in

about 5 minutes. Carefully wash the cover glass , aerator , and

beaker wall. Add 20 ml** of 4-percent ferric chloride solution, stir , wait one minute , and add 15 to 16 ml of phosphor icsulfuric acid mixture and 0.55 ml of diphenylamine sulfonate

indicator (stir after each addition). Titrate the solution

with 0.027 N potassium dichromate solution (added from a calibrated 100-ml bulb buret) until the maximum purple color is

obtained. Record the room temperature at the time of titration.

Pass the air at a rate of about 300 ml/min through cotton and

glass wool, a rotameter, a coarse frit under two inches of

sulfuric acid, a coarse frit under one inch of water, an empty gas-washing bottle, and the Branham-Sper ling bubbledispersion tube with its tip near the bottom of the sample

solution. All connections are made with cleaned, pure gum

rubber tubing.

To high-uranium solutions (equivalent to about 95 ml of

dichromate) add 30 ml (instead of 20) of 4-percent ferric

chloride solution, and 23 ml (instead of 15) of phosphor icsulfuric acid mixture.

42
Make corrections and calculate the uranium content from the net

volume and titer of the dichr ornate as directed in section CIO.

9- Standardization — titer of dichr ornate . Transfer

about 15 g of standard black oxide to a platinum crucible.

Ignite in the open crucible in an electric muffle at 900°C for

one hour. Cool over magnesium perchlorate in a desiccator;

crush and stir the oxide briefly; and rapidly transfer 1.500-g

portions to each of four small weighing bottles , closing each

weighing bottle immediately and firmly. Weigh accurately

15 to 20 minutes later. Remove at least three samples for each

standardization, as follows: Pour the sample into a lipped,

500-ml Erlenmeyer flask and obtain the sample weight by difference after correcting for any change in the tare weight. Wash

down the inside of the flask with 15 ml diluted H^SO^ (HI),

Add 10 to 15 ml of diluted nitric acid (1:1). Digest at 80 to 100 OC until reaction ceases. Wash down the wall with 25 ml of

diluted H

2 S0^ (1:1) and continue as directed in sections C.6,

C.7; and C.8.

10 . Calculation and selection of assay values . (a) Titration corrections . Determine the corrections needed to convert all observed dichromate volumes to volumes at 25 °C (from a chemistry handbook table of changes

in water volume with temperature).

Since the indicator does not give an end point in a blank

solution, determine the indicator correction indirectly as the

difference between the titration values of two 50-ml aliquots

43
of a uranium solution when one aliquot is titrated as a single

solution and the other aliquot is divided and titrated as two solutions. From 0.2 to 0.5 ml of dichr ornate is required for

the indicator.

Determine the correction for other reagents by carrying

a blank solution through sections C.3, C.4, C,5, and C.6,

combining a 50 -ml aliquot of the blank with one of two duplicate

aliquots of a uranium solution, then reducing and titrating

the two uranium aliquots alike. The reagent correction, or difference between the two titrations , has been small enough

to be omitted at NBS

Calibrate the buret and volumetric flasks, and provide

corrections if needed.

(b) U-^O q in sample . Obtain the net volumes of

dichromate by applying temperature, indicator, other reagent

and glassware corrections found as directed in section C.lOa

to each dichromate volume observed in sections C.8 and C.9.

Using the net volumes, and ignited No. 950a, designated as "R", on the 99.94$ U^Og basis, the following calculations apply.

(net ml of Kp Cr p 0

7 for sample aliquot )FA'

foU^On as rec'd = —<=—L X 100

^ (grams of total sample)

foU^On as rec'd

%\J^0n, dry basis = ^ x 100

? 100$ - (% loss on drying)

where

"As received" applies only if no leakage occurred between

receipt and analysis,

44
.

, _ volurre "before aliquoting in section C . 3b

Volume of aliquot in section C . yo

! TA

0.999^ x (grams of R in aliquot from section C . 9

') 1 ~ (net ml of K

2 Cr2 07 for R aliquot from section C.9) J

(R = ignited NBS Standard Reference material No. 950a)

« _ (volume before aliquoting in section C.7 ) (volume of aliquot in section C.7) 5 (net ml of K

2 Cr20^/gram of R from sections C.l-8)

B = -r- : > (net ml of K

2 Cr2 0 7/gram of R from section C.9)

The factor "B" is applied to- correct for a rather consistent

loss obtained in carrying samples of ignited standard black

oxide through the entire assay procedure. Usually one such

standard is run with each five umpire samples. The value

for "B" is the average for a considerable number of such runs and now is greater than 0.999 a"t NBS. It should be determined

by each analyst.

(c) U-^Oq reported . Report the average of one aliquot

each from two separate solutions providing the two values agree

within 0.06$. Otherwise^ report the average of two aliquots

each from two separate solutions providing the range of the

four values is not greater than 0.15$., or the average of one aliquot each of three or more separate solutions providing

the range of the three or more values is not greater than

0.2$.

45
D . Alternate Procedure Using Thioacetamide

Follow the basic procedure except modify sections C.3

and C.4 as follows:

C . 5-alternate -- Dissolution before thioacetamide use . (a) Small assay sample (1.5 to 2.0 g ). W-ash down

the inside of the flask with approximately 15 ml of water and

swirl to mix. Add 24 ml of diluted sulfuric acid (1:1) and

about 15 ml of diluted nitric acid (1:1). Digest at 80 to 100 °C until reaction ceases (up to one hour), swirling as heeded to keep the sample dispersed. Wash down the wall with

water and add up to one ml of hydrofluoric acid (48;$). Place

the flask on a fast heater and heat, while shaking the heater,

until the sulfuric acid refluxes nearly to the neck of the

flask. Remove from the heater; and when the flask is cool,

wash down the inside of the flask with 90 ml of water. Continue as directed in section C . 4-alternate

(b) Large assay sample (8 g) . Wash down the inside

of the flask with about 25 ml of water and swirl to mix. Add

25 ml of concentrated nitric acid. Digest at 80 to 100 °c

arid swirl occasionally until reaction ceases (up to one hour).

Cool and wash down. Cautiously add 55 nil of concentrated

sulfuric acid and mix. Add about 2 ml of hydrofluoric acid.

Place the flask on a fast heater and heat, while shaking the

heater, until the sulfuric acid refluxes nearly to the neck

of the flask. Cool. Cautiously add 200 ml (more for diffi46
cultly soluble material) of water and mix. Cover and digest

on a steam bath for 50 minutes. Cool to room temperature.

Filter through a 11-cm No. 40 paper into a 500-ml volumetric

flask. Wash with 100 ml of diluted sulfuric acid (2:98) and

several times with water. Ignite and weigh the residue.

(If it amounts to 0.1 percent of the sample , test the residue

for uranium as directed in the basic procedure, section C.j?c»)

Dilute the filtrate to nearly 500 ml while mixing the solution

by swirling. Cool it to room temperature. Dilute the solution

to the mark, mix thoroughly, note the temperature, and transfer

a 100-ml aliquot to a 500-ml Erlenmeyer flask. Before diluting

the aliquot, dry the stopper and neck of the volumetric flask

and close the flask tightly, so that a duplicate aliquot may be

obtained later if desired. To the 100-ml aliquot, add 9 ml of

diluted sulfuric acid (1:1). Continue as directed in section

C . 4-alternate

C . 4-alternate — Treatment with thioacetamide . Add a few

glass beads and boil gently to dissolve soluble salts. Cool

slightly, add a small portion of potassium bisulfite, and boil

to remove sulfur dioxide. Dilute to 100 ml, bring to a boil,

and continue to boil gently while adding o to 10 ml of 2 percent thioacetamide in 2-ml portions. Continue to boil gently

to coagulate the precipitate. Remove and filter while hot

through an 11-cm No. 40 paper into a 500-ml lipped Erlenmeyer

Use less than 8 ml if amount of impurities is very small.

47
flask. Wash thoroughly with cold water (to obtain at least

200 ml of filtrate). Add glass beads. Boil the filtrate

until the hydrogen sulfide is removed, or until the volume

reaches 90 ml. Add a small portion of ammonium per sulfate,

and continue to boil until the volume is 75 to 80 ml . Proceed

with the extraction of cupferrates as in the basic procedure,

section C.5.

E. Modification for Portuguese Concentrate (about 10 percent

Uranium ) Follow the basic procedure with the following changes:

1. Assay on the dry basis; use 6-g samples for assay.

2. After proceeding through basic procedure sections

C.^b and C.4 3 boil down to 60 ml and add 2 percent potassium

permanganate dropwise until the uranium solution is pink.

Chilly transfer to a separatory funnel, and dilute to 80 ml.

Treat with 40 ml of cupferron and extract with 60 ml of

chloroform, then 25 ml of chloroform; followed by 15 ml of

cupferron and three 2 5 -ml portions of chloroform; then 10 ml

of cupferron and three 2 5 -ml portions of chloroform.

3. In section C.5j> omit the addition of sulfuric acid

after extraction.

4. Follow section C.6 as footnoted.

5. In section C.lOb, because of the modified aliquoting

procedure, use "T" instead of "F" and calculate as follows:

(net ml of Kp Cr p 07 for sample aliquot )TA'

^U.Oo as rec'd = —=-i x 100

^ (grams of total sample )B

48
F. Modification for Refined Orange Oxide

The summary below indicates how the basic procedure was extended to visual indicator titration of solutions containing

about five grams of uranium. Although subsequent studies of

high-accuracy analyses of uranium standards have suggested even further modifications, particularly in regard to controlling

the acidity in step 2 a using a still smaller reductor, preventing_physical loss during aeration, determining the U(III)-

U(IV) end point and measuring the reagent blank, the details of

those studies are beyond the scope of this paper. The following method has given adequate results for material having an 0.1-percent splitting limit and not requiring separations.

1. Follow the basic grab-sampling procedure except take

samples weighing about 6 g. Weigh by difference of the closed

weighing bottle before and after transferring the sample to a 500-ml Erlenmeyer flask.

2. Add 30 ml of perchloric acid and heat over a medium

hot plate with care to prevent boiling and to control the

amount of acid lost by evaporation. Try to avoid swirling any

solid up on the flask wall. Be sure the sample is completely

dissolved; examine closely.

3. Dilute the above solution, containing about 25 ml of

perchloric acid, to approximately 100 ml. Mix. Cool to room temperature

4. Use a small Jones reductor, with a 10xl50-mm column of

zinc amalgamated with two-percent mercury; and collect the

49
reduced solution in a 750-ml Erlenmeyer flask. Clean the

re'ductor by washing with about 200 ml of diluted sulfuric acid

(5:95) and then with water. Reduce the samples by passing

through the reductor in the following order: about 20 ml of

diluted sulfuric (5:95) , the uranium solution, 200 ml of diluted sulfuric acid in four portions , and finally 100 ml of water

in three portions. Allow each wash to drain to the top of the

amalgam before the next wash is added. Decrease the flow rate

of the uranium solution to insure sufficient reduction for some U(III) to persist until aeration. During the washing with acid,

return to the normal flow rate, to minimize gas entrapment and

possibly poor removal of uranium from the reductor.

5. Stir with a "cooled" magnetic stirrer while aerating

for one-half hour. Use a spray trap made, for example , by passing the bubbler tube through a stemless funnel recessed into the

flask, adding a few beads to the funnel and squirting diluted

sulfuric acid (5:95) into the funnel and around the neck of the

flask. After aeration, wash down the walls of the funnel with

diluted sulfuric acid (5:95) and transfer the solution to an 800-ml beaker. During aeration the color of the sample changes

from dark green to olive green and finally to transparent green.

6. Add the calculated amount of accurately-weighed potassium dichromate (NBS Standard No. 136b) to oxidize 99 percent of

the uranium. Stir for one minute after complete solution.

-* The transfer of an appreciable amount of heat from the

stirrer to the solution is avoided by placing a wet cloth

or a water bath between the stirrer and the flask.

50
7. Add 20 ml of 4-percent ferric chloride solution,

stir for two minutes, add 23 ml of phosphor ic-sulfur ic acid

mixture, and stir to mix. Add 1.00 ml of 0.00^ M indicator

and titrate as in the basic procedure except over a 200-w

light bulb and from a 25-ml buret.

8. Apply the vacuo correction to the weight of dichr ornate used in step 6. Add to the dichromate used in step 7 and

convert to uranium.

G. Modification for Solutions Containing about 10 mg of Ur anium

Use the basic procedure with the following exceptions:

1. Prepare modified reagents as follows:

(a) Standard potassium dichromate solution (0.01 N)

Transfer 1 g of potassium dichromate (NBS Standard No. 136b)

weighed to 0.1 mg, to a 2-liter volumetric flask, dissolve

in water, dilute to the mark at room temperature, and mix

thoroughly.

(b) Stock uranium solution (4 mg U^0g/ml and 0.04 ml

H

2 S0^/ml). Prepare as in the basic procedure, section C.9,

except use 2.00 g of ignited standard U-^Og and dilute with

water to 500 ml (in a volumetric flask, at room temperature).

Record the dilution temperature, and mix well.

(c) Dilute uranium solution (0.2 mg U-jOg/ml and

0.01 ml HgSO^/ml). Transfer a 50-ml aliquot of modified

reagent- (b) to a 1-liter volumetric flask. Add some water

51
and 8 ml of sulfuric acid. Swirl to mix. Cool to room temperature, dilute to the mark with water, and mix.

(d) Sodium diphenylamine sulfonate indicator

solution , 0.002 M. Dilute one volume of the 0.01 M solution

(from basic procedure) with four volumes of water.

(e) Jones reductor. Prepare as in the basic

procedure but use only one-third as much amalgam, making a 10xl50-mm column of ten-percent amalgam.

2. Use glassware reserved for this level of uranium, or freshly cleaned for this purpose.

5. After dissolving and separating the uranium from

interferences, including easily oxidized organic matter, fume

the uranium solution, containing about 12.5 ml of sulfuric acid,

as in the basic procedure, section 0.6, except make the fourth

fuming on titration day. Use extra care during each fuming of

solutions that precipitate and tend to bump. Watch constantly.

When precipitation begins, immediately remove the flasks from

heat, cool slightly, and fume at a slower rate until sulfuric

acid refluxes to about one inch, then increase the heat and

finish fuming.

4. Before the fourth fuming add a 50-ml aliquot of modified reagent (c) to each sample containing less- than 5 nig of

uranium.

52
5. Also prepare "direct control" samples as follows:

Into each of three lipped 500-ml Erlenmeyer flasks, pipette

50.0 ml of modified reagent (c). To each of two of the flasks,

add a second 50-ml aliquot of modified reagent (c), and label

"20 mg". Label the other one "10 mg" . To the "10 mg" flask,

add 12 ml of sulfuric acid; and to each of the "20 mg" flasks,

add 11.5 ml of sulfuric acid. Add a few beads, boil down,

and fume once.

6. After the fourth fuming of the samples and one fuming

of the "direct controls", dilute each solution with 80 ml of water. Mark the level, boil to dissolve any salts, and redilute

to the mark. If insoluble salts persist, dilute to about 120

ml and boil down to the mark.

7. Oxidize the solution with 2-percent potassium permanganate (heat to boiling) and cool to room temperature. Make

sure the solutions are diluted to the mark or slightly higher,

and mixed after dilution.

8. Use the small reductor (freshly washed with diluted

sulfuric acid) and reduce in the following order:

one "20 mg" direct control

one "10 mg" direct control

all sample solutions (not over 11) one "20 mg" direct control

Avoid draining solutions below the top of the amalgam. For

small amounts of uranium, it is more important to limit the

entrance of air into the reductor than to get sharp separations

53
of successive washes. Make all reductions. Then proceed

promptly with step 9j> and titrate the solutions in the same order that they were reduced.

9. Aerate for 12 minutes . Add 15 ml of the filtered

ferric chloride reagent, 15 ml of phosphor ic-sulf uric acid

mixture, and 1.0 ml of 0.002 M indicator (stir after each

addition). Titrate with 0.01 N K

2 Cr

2 0^ (added from a 25-ml

buret) until the maximum purple color is obtained. Make cor- rections and calculate the uranium content from the net volume

and titer of the dichromate. Use the "direct control" results

for judging whether there was significant air oxidation of the

dilute solutions (and for calculating appropriate corrections

if required )

.

* The length of time is not critical; it is important that

all solutions in the group be aerated alike.

5^
5. SUMMARY

Between 1949 and 1964 the National Bureau of Standards

performed umpire analyses of several thousands of uranium con- centrate samples resulting from the uranium procurement program

of the U. S. Atomic Energy Commission. These represented more

than 50 producers located in widely scattered areas of the

world. All samples were analyzed by one standard assay method,

including dissolution with acids, removal of interferences by

sulfide precipitation and chlor of orm-cupferr ate extraction,

reduction in a Jones reductor, and titration with potassium

dichromate. A basic procedure applicable to all types of material was developed and standardized by means of known amounts

of uranium provided by NBS standard reference material No. 950a.

The primary problem in the assays was the establishment of a. reliable sampling weight base line. NBS conducted studies that

contributed to a. better understanding and control of this problem, and the later replacement of the usual "drying-to-constantweight" basis with the "as received" basis. A comprehensive

account is given of NBS experiences in connection with the

identification and the solving of uranium concentrate assay

problems

55
6 . APPENDIXES

APPENDIX A

Details of INX Studies

Bottles No. 1 and 2 were filled from different lots at Fernald sampling plant on 9-28-56 , opened at NBS on 1-24-57 , emptied on 2-22-57; cleaned and treated alike until the base

weights were obtained on 2-24-57. Their interiors were care- fully dry-cleaned with Kimwipe tissue and their exteriors were cleaned by scraping off the labels , using damp tissue to remove

all glue and loose material, and finally drying with dry

Kimwipe s

.

Bottles No. 5j 4, 5? and 6 were four unopened reserve bottles sealed at Fernald in 1956 on 9-28, 9-28, 4-11, and

4-19, respectively, and included two (No. 5 and 4) filled from

the same lots as No. 1 and 2. The closures of No. 3, 4, 5,

and 6 were not disturbed, but the exteriors were cleaned like

No. 1 and 2. All six of the cleaned, marked bottles were stored together in the laboratory atmosphere for 44 hours just

before their base weights were obtained.

During the first month, the NH^N0^-H

2 0 mixture (under

bottles No. 1, 3, and 5) was stirred magnetically as needed to maintain approximate saturation. Due to fluctuations in room

temperature, the surface of the NH^NO-^ solution was less than

saturated during the latter months of the experiment.

56
The relative tendency of the different parts of the taped

and waxed cap to lose moisture was determined as follows: On

6-26-57 one bottle (No. C) each from two lots bottled on 9-29-56 and 2-7-57 were carefully opened and the cover of each

was separated into three portions: sealing wax and tape, cap

liner , and bare cap. No solvents were used, and the six test portions were left exposed to the room air for two hours before

the base weights were taken. Then the test portions were stored in the same desiccator used for the earlier dry-air

storage experiment. Losses of weight were observed as shown

in figure 3 of the text.

790-939 0-65-5 57
APPENDIX B GRAND JUNCTION URANIUM CONCENTRATE

STANDARDS PROGRAM OF 1958

Summary

Because of the high backlog of uranium umpire requests in

1958j a means was sought to qualify private laboratories to act 'as umpire assayers. Representatives of Grand Junction AEC

Office , of its Sampling Plants and of NBS decided that each

interested laboratory should be furnished a suite of standard

samples upon which the average assay and confidence limits had

been accurately determined; the laboratory would be considered

acceptable if it were able to assay each standard sample within

the established confidence limits. Subsequently 3 Lucius Pitkin,

Inc., carefully prepared 100 pulps each of seven different

materials 5 representing the various types of uranium concentrate

produced on the Colorado Plateau. Two pulps each of three of

the materials were submitted to each of the five laboratories

(LPI, MCW, NBL, NLOj and NBS) then analyzing uranium concentrates for the USAEC . Each laboratory analyzed each of its

six pulps in duplicate by each of the four methods proposed

for establishing the sampling base line, as follows: the "as is" basis, regular drying at 110 °C, controlled atmosphere

drying at 110 °C, and ignition at 900 °C. The results indicated that only the "as is" method was a reliable basis at that time, and even for it, more detailed

specifications of sampling conditions and procedures were

58
needed to obtain confidence limits suitable for standard samples. There was some evidence that some of the "as is" results

were biased by moisture pickup during sampling.

The specification for the "as is" method was simply to weigh out duplicate samples as quickly as possible. However 3 NBS did all of its sampling for this study in a dry box to insure both that all of its samples were started on one reproducible basis and that its "as is" basis was not biased by the

high humidity of summer in Washington. An outline of the NBS

sampling and analysis procedure given below was furnished to the other laboratories before the standards were sampled,, but

in this program (1958) s each laboratory had considerable

latitude in deciding what sampling details to observe. The

following information is given as background for possible

future studies.

GJOO Procedure for Preparation of the Standards

(a) Combine the dried; 115-mesh sample rejects on hand

from each mill (Anaconda, Durango, etc.).

(b) Mix this combined quantity (approximately 35 lbs)

for seven hours in a Y-blender equipped with an intensifier bar.

(c) Remove the mixed material from the blender and place

promptly in stainless steel drying pans and dry in a forced

draft oven for 48 hours at a constant temperature of 110°C.

(d) At the end of the drying period, two or three people

should transfer as rapidly as possible approximately equal

portions of the concentrate from each pan into predried Mason

59
sample jars with Kerr lids (approximately 100 grams per jar,

120 pulps per material type).

(e) The half-pint Mason jars and Kerr lids should then

be placed in an oven and dried for 24 hours at a temperature

of 110°'C, removed, capped, and sealed immediately while hot.

Specifications of Analytical Methods for the Program

(a) "As is" Method - Weigh out duplicate samples as quickly as possible and assay by the usual procedure.

(b) "Regular" Method - Weigh out two more samples for

determination of moisture in the usual way. Dry these samples

at 110°C at room atmospheric conditions, but keep a record of

the temperature and relative humidity during the weighing and

drying operations. Report any losses and gains in weights,

and correct the assay sample weights for any moisture losses.

Consider gains as zero loss, but record and report separately.

(c) "Special Drying" Method - Repeat Method No. (b)

except perform all weighing and drying of the moisture samples

under controlled humidity conditions of not greater than 10$

relative humidity (i.e., 0.936 grains H

2 0/cubic foot of air

at 75 °F)*.

(d) "ignition" Method - Weigh out two more samples and

heat slowly in a muffle furnace to an ignition temperature of

900 *°C - 25 °C and hold for a period of one hour. Weigh the

ignited sample and record the loss on ignition; then assay the

ignited sample.

^. This is equivalent to < 0.002 g HgO/g dry air.

60
Procedure for Sampling and Analyzing USAEC Standard Concentrates

Nos. "Dj " "E ^ " and "F" at NBS , as Revised 8-4-38

Sample one material per week, grabbing all 32 samples from

the two bottles in a dry box at a single sitting, as detailed

below in steps (l) through (7). Reserve half of the samples,

designated A' through H-2 ' , for rechecks or extra data as needed.

Assay only four samples (two as is and two after • ignition) from

each bottle, and use the loss-on-drying values to calculate the

other assay values. Have any given operation performed by a single analyst for all standard samples.

(1) Place in the dry box the two bottles of sample (with

sealing wax removed); two unweighed, glass— stoppered, 40x50-mm

weighing bottles; 16 weighed 40x50-mm weighing bottles, plus

four tares (two for dry-air and two for regular drying);

16 weighed 25x40-mm weighing bottles, plus two tares; a Scoopula; a small brush; a small fast balance (30-g capacity,

for estimating 1.5 g); weights; forceps; wiping tissues; and

an 8xl0-inch pan.

(2) Flush the box overnight with a slow stream of air

dried by passing through magnesium perchlorate.

(3) Mix the samples.

(4) Open and line up the weighing bottles and tares for

a set of eight samples, A through H: A for regular loss 5 to 10 g

_B for dry air loss 5 to 10 g

_c for "as is" assay 1.4 to 1.6 g 61
_d for ignition loss and assay 1.4 to 1.6 g

_e for ignition loss and assay 1.4 to 1.6 g f for "as is" assay 1.4 to 1.6 g

Or for dry air loss 5 to 10 g H for regular loss 5 to 10 g

(5) Break the seal on one bottle of sample Immediately

pour at least 50 g into an unweighed bottle 3 stopper it firmly , and reserve for the duplicate, A' through _H' , set. From the

remainder, grab the A through H set (in 5 to 10 minutes).

Stopper each weighing bottle immediately after the sample is

put in it, and handle the tare bottle like a sample bottle.

(6) Open and line up the weighing bottles for a second

set of eight samples, and grab the A' through H' set from

the reserved portion.

(7) Repeat steps (5) and (6) with the second bottle of

sample for sets A2 through H2 and A2

through H2 '

(8) Sort the 38 weighing bottles into four groups as follows

A, A2, H2j and tare Nj B }

Gv, B2, G2^ and tare D;

c s d, _e, f_, c2 , d2 , e2 , f

, and tare s^; all reserve samples and tares. Rapidly transfer the weighing bottles from the dry box to desiccators freshly charged with magnesium perchlorate; use a separate desiccator for each group. Wait 30 minutes. Then

weigh initially in the following order:

62
tare A, A2, tare B 3 B 3 B2 3 G3 G2 3 K, B2 3 tare N (to dry);

tare s } c_3 c23 f 3 f2_3 (to run for "as is assay);

tare s_} 6. 3 6.2 3 e_5 e2 3 tare js (to ignite and assay);

tare s_' , 3 c2 ' s f

, f2 T , 6<

3 62 1 3 _e ' 3 e2', tare _s' (to reserve);

tare N 1 3 A

3 A2 1 , tare D' 3 B 1 , B2 ' , G' , G2 1 , H 1 3 H2 1 , tare N' (to reserve).

Have a second analyst repeat the whole series of weighing.

(9) Allow .A, A2 3 B, B2 3 and tare N to stand in room air

for one hour. Reweigh to determine if the material gains

significantly in closed weighing bottles.

(10) Pour the c_3 c2j and f2 samples into 500-ml

Erlenmeyer flasks 3 and the 6_ 3 62, e_ 3 and e2_ samples into Coors

No. 0 porcelain crucibles previously ignited and weighed with

a tare crucible. Close each weighing bottle Immediately after

emptying,, and handle the tare weighing bottle in the same manner as the others.

(11) Wait 30 minutes and weigh the empty weighing bottles

as in step (8).

(12) Dry A, A2, E 3 B2 3 and tare N together (in normal

air )

.

(13) Dry B, B2 3 G3 G2, and tare D together (in dry air)

as follows: Heat the samples at 110°C in a small oven (3.7-liter

capacity and designed for vacuum drying but used as a normal

pressure oven) through which air from a drying train is circulated at a rate of 200 to 250 ml per minute. [The drying train

consists of two 32-mm-diameter columns containing a total of

63
about 200 g of magnesium perchlorate, preceded by three similar

columns containing about 400 g of indicating silica gel. The

silica gel is replaced as often as necessary to prevent any

visible color change (from deep blue to either light blue or pink) in the column next to the magnesium perchlorate. The

silica gel is regenerated by drying alone in an oven at 110 °C. ] Close the weighing bottles rapidly before removal from the

oven. Cool over fresh magnesium perchlorate. After one hour.,

loosen each cap momentarily (to equalize pressure) and reclose

firmly. Leave another hour; then weigh.

(14) Ignite d. 3 d2 3 e2_, and the tare together } heating

them from 25°C to 900°C in four hours and then igniting at 900 °C for one hour. Cover the hot crucibles and cool only two

in each desiccator. Uncover just before weighing, and weigh

as rapidly as possible after opening the desiccator.

(15) Transfer the ignited samples to 500-ml Erlenmeyer

flasks, by pouring out the bulk; dissolving the remainder with

diluted HNO-j (and HC1 if needed) } and finally washing with

water. Assay with the c_ } _c2, f_, and f2 samples. (Note whether

material reacts with the crucible glaze.)

(16) Ignite two reserve samples, d

1 and e2_' s as in

step 14 except repeat the ignition for l~hour periods until

constant weight is obtained.

64
NBS Results

The results in tables 2, 5* and 4 are values for samples

obtained as described above*. The additional results in

tables 1 and 5 involve several experimental variations.

There is some uncertainty about the values for bottles I and II of "D" because of the sampling in helium. However , in

two respects, the "as is" assay and the dry-air loss , there is

good agreement of the original results for bottles I and II in table 1} with those for bottles m and TV, in table 2. The later samples , _i, j_, and k, listed in table 5 and taken

one hour to 11 days after removal of bottles D.I,, B.Il, and

D.III from the dry box, showed changes of 0.05 to 0.70 in the

"as is" assay.

For each of the standards, all of the original samples

showed good reproducibility on the "as is" basis, whether the

samples were assayed directly or after ignition. Also, each

pair of duplicate ignited samples listed in tables 1, 2, 3,

and 4 agreed on the ignited basis.

Equally good agreement was not obtained for all recheck

assays on the ignited-f or-one-hour basis listed in table 5. The results of tests 1, 4, and 6 (table 5) indicate that it

may be necessary to ignite the samples at 900 °C for two or three hours in order to obtain constant weight. Furthermore,

*M S Richmond did all sampling and initial weighing, _ i.e .

,

through step 9. J. R. Baldwin checked the initial weighings

and made all assays and loss determinations.

65
Table 1. NBS initial results for standard, concentrate "D Bottles I and. II (sampled in helium on 7-21a

; titrated on 7-30-58).

Bottle % U^Og on % Loss % Change at 110°C

Sample "As is" basisb at 900°C Dry air Regular0

D.I A

' ~ +0,^5

B - -O.56

c 83.26 -

d - 83.31 8.37

e - 83*30 8*47 f 83.30 -

G - -0.52

H - +0.32

D.II A - +0.32

B - -0.55

c 83.26 -

d - 83.29 8*45

e - 83.31 8.44

f 83.33 -

G - -0.51

H - - - - +0.33

Average of 2 determinations

D.I 83.28 83.30 8.42 -0.54 +0.32

D.II 83.30 83.30 8.44 -0.53 +0.32

Average of 4 determinations

D.I, D.II 83.29 83.30 8.43 -0.54 +0.32

aThe initial weights of the weighing bottles plus samples were not constant due to exchange of helium and air through the

ground -joint of the weighing bottle. Results in table 1 are based on weights obtained after storing the weighing bottles

plus samples in a desiccator for about 20 hoursj the desiccator

was opened and closed a number of times during the first 3 hours

^Although _d and e^ samples were ignited before assay, all results

were calculated from the "as is" weights of the samples. The

c_, f s and fj_ samples were assayed directly.

c Value is for the minimum gain, obtained on 7-30, when the relative humidity was 59^ at a temperature of 77°F (equivalent to 5.9 grains Hp 0/cubic foot of air, or 0.012~g H? 0/g dry air).

66
Table 2. NBS initial results for standard concentrate "D",

Bottles III and IV (sampled in dry air on 9-5;

titrated on 9-12-58).

Bottle % U-^Og on % Loss % Change at 110°C

Sample "As is" basis a at 900°C Dry Air Regularb D.III A - - - - +0.14

B - - -0.54

c 8^.23 -

d - 8^.24 8.39

e - 83*25 8.35

f 83.22 -

Gr - -0.53

H - - - - +0.15

D. IV A - - - - +0.14

B - -0.51

c 83.31

d - 83*19 8.34

e - 83.21 8.33

f 83.20 - G - -0.53

H - - - - +0.13

Average of 2 determinations

D.III 83.22 83.24 8.37 -0.54 +0.14

D.IV 83.26 83.20 8.34 -0.52 +0.14

Average of 4 determinations

D.III, D.IV 83*24 83.22 8.35 -0.53° +0.14

Although the _d and e samples were ignited before assay, all

results were calculated from the "as is" weights of the

samples. The c_ and f samples were assayed directly.

bValue is for the minimum gain, obtained on 9-8, when the relative humidity was 48$ at a temperature of 76°F (equivalent to 4.6 grains H

2 0/cubic foot of air,, or 0.009^~g H^O/g dry air).

c Two reserved samples gave loss values of 0.6 in 15 hours or 0.7 in 32 hours when dried in the bone-dry air described in

Appendix D.

67
Table 3. NBS initial results for standard concentrate "E" (sampled in dry air on 8-8; titrated on 8-15-58).

Bottle % U^Og on % Loss % Change at 110°C

Sample "As is" basis a at 900°C Dry air Regular

E.I A - +0.02

B - -0.02

c 78.42 -

d - 78.48 1.11

e - 78.48 1.10

f 78.45 -

G - -0.02

H - - - - +0.02

E.II A ~ +0.02

B - -0.02

c 78.44 -

d - 78.44 1.07

e - 78.48 1.12

f 78.44 - G - -0.02

H - - - - +0.02

Average of 2 determinations

E.I 78.42 78.48 1.10 -0.02 +0.02

E.II 78.44 78.46 1.10 -0.02 +0.02

Average of 4 determinations

E.Ij E.II 78.43 78.47 1.10 -0.02 +0.02

Although the d_ and _e samples were ignited before assay, all

results were calculated from the "as is" weights of the sample

The _c and _f samples were assayed directly.

*Value is for the minimum gain, obtained on 8-9, when the

relative humidity was 46$ at a temperature of 79°F (equivalent

to 4.8 grains Hp 0/cubic foot of air, or 0.010 g Hp 0/g dry air)

68
Table 4. NBS initial results for standard concentrate "F" (sampled in dry air on 8-20; titrated on 8-28-58).

Bottle % U^Og on % Loss % Change at 110°C

Sample "As is" basis a at 900°C Dry air Regular13

F.I A - +0.03

B - - - -0.05

c 85.53 -

d - 85.64 1.00

e - 85.65 O.98

f 85.65

G - -0.06

H - - - - +0.03

F.II A - - - +0.04

B - - -0.06

c 85.59 - - -

d - 85.62 0.95

e< - 85.66 0.86

f 85.65 - G ' - - -0.06

H - - - - +0.03

Average of 2 determinations

F.I 85.59 85.64 O.99 -0.06 +0.03

F.II 85.62 85.64 0.90 -0.06 +0.03

Average of 4 determinations

F.I, F.II 85.60 85.64 O.95 -0.06 +0.03

aAlthough the d^ e^ and e' samples were ignited before assay,

all results were calculated from the "as is" weights of the

samples. The £ and f samples were assayed directly.

bValue is for the minimum gain, obtained on 8-28 , when the

relative humidity was 58^ at a temperature of 75°F (equivalent

to 5.5 grains HpO/cubic foot of air, or 0.011**g HpO/g dry air).

69
Table 5. NBS recheck and initial average results.

Test

No. Bottle

Sample Date

Ignited

7o Loss at

1 hr. 2 hr. 900°C

3 hr. „ A

. X

„U3°i As-is

a^Ignite

IA D.'l,D.II 7-23-58 8.43

b 83.30° 90.97

1 D.II.e'

D.I.d' 8-4,5,9

8-4,5,9

8.57 8.60

8.66

8.65

8.68 8.66

83.26

d 91.06

2 D.I.i

D.I.j

D.II.i

D.II.

j

7-23

.._

8.59

8.58

--— —

--

82.98°' e 82.87

C ' e 82 .96°' e 82.99°' e

90.78

90.78

3 D.I.k D.II.k

8-5

8-5

9.05

9.47 —

-- 82.97^ 82.54

91.22

91.17

IA D.III,D.IV 9-6 8.35 83.23 8 90.81

4 D.III.d'

D . IV . d

1 9-8,9,10

9-8,9,10

8.35

8.25

8.61 8.59 8.64

8.62

5 D.III.i

D.III.j

D.III.f* --- --

83.208' h 83.15 g ' h

83. 201 —

IA F.I,F.II 8-23 0.95 85.62 86.44

6 F.I.d 1 F.II.d' 9-6,9,10

9-6,9,10

0.65

0.62 0.890.89 0.940.96

aThe "as-is" assay was calculated from the as-sampled weight and the ignited assay from the ignited-one-hour-at-900°C weight.

Initial averages (from tables 1, 2 or 4) are underlined.

°Titrated on 7-30-58.

dTitrated on 8-15.

6 Sampled two days after removal of D.I and D.II from the dry box. ^Sampled 11 days after removal of D.I. and D.II from the dry box; and titrated on 8-8.

8Titrated on 9-12. ^Sampled one hour after removal of D.III from the dry box. titrated 1-15-59.

70
since the samples used in test 1 were duplicates of (and

sampled at the same time as) the initial samples of D.I and

D.II and agreed with them on the "as is" assay basis, the

three-hour loss values in test 1 compared with the initial

average one-hour loss for D.I and D.II suggest that all onehour ignition losses obtained on 7-2^ may be about 0.25 percent

below constant weight. If so, the ignited-to-constant-weightbased assay for original samples of D.I and D.II is 91.21 percent, and for the later samples i and of D.I and D.II may be

91.03 percent. Similarly, the results of Tests 4 and 6 indicate that all one-hour ignition losses obtained on 9-6 may be

about 0.3 percent below constant weight and that the ignitedto-constant-weight-based assay for D.III and D.IV is 91.09 percent. On the other hand, comparison of the initial average

loss value for F.I and F.II with the results in Test 6 for other

original samples indicates that constant weight was sometimes

reached in one hour. If that occurred in Test ~5

} then all NBS

values for "D" on an ignited-to-constant-weight basis would fall

between 91,03 and 91.22 percent. Some of the difference in NBS

one-hour ignition loss values may be due to the variations that

occurred in manually changing the furnace rheostat in the four

hours before the temperature reached 900 °C. The only evidence found of material reacting with the

glaze of the porcelain crucibles was an 0.5 mg gain in the

weight of- each crucible used for igniting 1.5 g of either

Standard "E" or another Vitro sample. There was no visible

71
stain, and no significant difference in the "as is" basis

values for samples whether assayed directly or after ignition.

Tare corrections were made., and all weighing bottles for

A through E samples were stored in desiccators. The _ij> j_3 and

k analysis samples were taken in room air and not put in desiccators; i.e. , they were sampled exactly like umpire samples

except for the delay between first opening the bottle and

sampling the material.

All A, _Bj 9l> and E. samPles were heated at 110°C for a five-hour interval followed by two approximately l6-hour

intervals. The A and H samples were heated simultaneously

with the B and G samples. The time required for obtaining the

minimum weight in normal air varied from 5 to j>8 hours „ In dry

air, "D" material lost 0.16 percent in the first five hours.

Interlaboratory Evaluation

The results from all five laboratories were analyzed

statistically by Dr. W. J. Youden of NBS . He found that the

data did not properly qualify for establishment of confidence

limits by application of statistical formulas and expressed

the feeling that these data should be evaluated by a scrutiny

of the individual results. This is provided in the following

detailed statistical analysis by Dr. Youden supplemented by

the notes based on laboratory observations.

In figure 1, Dr. Youden has compared the five laboratories

by plotting their deviations from average assays (tabulated in

Dr. Youden 1 s table 2); the deviations of "as is" assays are

72
plotted against those of "regular drying" assays. The No. 3 and No. 5 laboratories had high results; the No. 2 3 low; and

the No. k, erratic } with reference to the average for all five

laboratories. Since the points tend to lie along a 45° line,,

it was concluded that both methods showed the same bias.

Actually , this apparent similarity was due to (1) the gains

observed during "regular drying" being considered as zero loss,

and (2) the samples being prepared in a dry climate and vacuumsealed while hot } a method that prevented the occurrence of any

significant loss during regular drying.

790-939 0-65—

(

73
ANALYSIS OF DATA ON THE URANIUM CONCENTRATE

STANDARD SAMPLE PROGRAM*

The average difference between duplicates

(a) Run by same analyst on same bottle 0.057

(b) Run by same analyst on different bottles 0.064

(c) Run by different analysts (same lab) same bottle 0.061

(Somewhat over 100 pairs of duplicates for each case.)

I conclude that there is no difference between bottles and that

analysts in the same laboratory check each other.

Some of the data was discarded so that four determinations

were taken for each sample } by each method, for each laboratory. The ranges for these four determinations are shown in

table 1. There are 15 such ranges for each method and the average

ranges were Avg range for four

For "as is" sample 0.109

For "regular method" 0.104

For "special drying" 0.094

Avg for all 45 ranges 0.103

I conclude that the reproducibility is the same for all three

methods 0

Written by W. J. Youden, March 6, 1959 » except for footnotes

regarding laboratory observations,

74
Table I. Statistical analysis of ranges for 45 sets of four determinations (for three samples, by three methods of base line establishment, in five laboratories;

„

Lab. As is sample Regular method Special drying

No.

D E F D E F D E p l_id DO la averag<

1 .12 .07 .05 .22 .03 .14 .27 .03 .06 .11

2 .07 .10 .11 .05 .06 .10 .06 .02 .04 .07

3 .11 .02 .12 .11 .02 .12 .10 .02 .13 .08 4 .19 .29 .09 .16 .23 .04 .09 .07 .20 .15

5 .13 .13 .04 .07 .13 .09 .08 .15 .09 .10 Method

average .109 .104 .094 .103 Sample average

D .122

E Q91 Average range for sample of 4 = 2.059 o

Y .095 Estimate of a = 0.05

There are fifteen ranges that can be averaged for each

sample: _^Yg r ange for four

Sample D 0.122

Sample E 0.091

Sample F 0.095

There is no* reason to expect greater ranges for one sample

than another.

This is based on the analysis of only the assay results.

From the results for % change at 110 C, in tables 1-4, it can be seen that sample D varied more than the other samples

with atmospheric moisture changes. (Laboratory observation)

75
There are nine ranges from each laboratory and the average

range for each laboratory follows:

Laboratory Avg range for four

No. 1 0.11

No. 2 0.07

No. 3* 0.08

No. 4 0.15

No. 5 0.10

There is a two-fold spread between 0.07 and 0.15 which is

large enough to suggest a real difference between laboratories,,

The data suggest that the largest range., 0.15., is a bit out of

line. Mere reproducibility is only one aspect of the problem,,

perhaps the minor one. Table 2 shows the averages for the same four determinations

used to get the ranges shown in table 1. The row of averages

is our first interest. Clearly there is no difference between

the results with the "as is" and "regular" methods . The

special drying does have an effect^ and this depends^ as would

be expected,, upon the sample. The largest effect appears for

sample and here the laboratories show pronounced disagreement. Laboratories No. 4 and No. 5 run sharply higher than

the others on the special drying in the case of sample D.

* NBS. This is because the "regular" method gave gains (except for

a few small losses in Colorado) , and the gains (of up to 0.25) were considered zero loss. (Laboratory observation)

76
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77
The deviations for each laboratory from the average of all

the laboratories is also shown (in both table 2 and figure 1).

These deviations are particularly instructive , especially when

the "sample D - special drying 1

' set are set aside. Note that

No. 2, the laboratory with the smallest range (0.07) is

+.20 I r

DEVIATION "AS IS " METHOD

Figure 1. Graphical diagnosis showing groupings of

deviations by laboratories.

78
consistently low . Indeed the average amount low is 0.15 and

represents a serious bias either for this laboratory or the

others. Laboratories No. 3 and No. 5 are consistently high,

the deviations all being positive. Note that these averages

of +0.09 and -0.15 are far in excess of what would be expected

considering the reproducibility as revealed by the average

range. The average range for a sample of four is 2.059a. The

average range, 0.103, divided by 2.059, gives 0 . 05 as an estimate of the standard deviation of a single determination, con- sidering only reproducibility within a laboratory.

Each laboratory is represented by 9^4 or 36 determinations

in table 2. The laboratory average would have a standard

deviation of 0.05 / \/3^ or about 0.01. Clearly the scatter

of the laboratory averages, as revealed by the deviations:

No. 1 -0.01

No. 2 -0.15

No. 3 +0.09

No. 4 -0.02

No. 5 +0.09

demonstrates beyond question the existence of substantial

laboratory biases. It is not the role of statistics to single

out the laboratory with the smallest bias. The data suffice

This appeared to be due in part, at least, to a pickup of

moisture during sampling, as evidenced by loss-on-drying

values that did not agree with known climate variables.

(Laboratory observation)

79
to detect a difference between biases of x 2 = 0.05

The spread here is from +0.09 to -0.15 or 0.24. In summary we find., as usual, that differences in precision

from laboratory to laboratory are minor and quite unimportant.

The methods agree very closely because each laboratory apparently carries over into each method the same bias. There are pronounced differences between laboratories in these biases

and the problem really resolves into one of finding out who is

right. If the laboratories all run the same standard sample

and adjust their results on unknowns by whatever discrepancies

they find on the standard sample s the laboratories will be

brought into agreement. If a sample of known content is used,, we can decide which laboratory has the least bias - pending

that, no one knows.

Anyone impressed by a majority vote would pick No. 1 S No. and No. 5 to establish a consensus. These three laboratories do consistent work as revealed by the three samples,

and yield a general average with which each of three laboratories agree quite well.

¥. J. Youden

March 6, 1959

80
APPENDIX C Summary of Drying Tests on IMCC Material at NBS

Three samples of Florida green salt material^ representing

IMCC Lots 5 3 and 6, were received at NBS on 10-24-56. Each

bottle was completely sealed with wax. Immediately after the

seals were broken on 10-28-56^ eight samples of each lot were

rapidly transferred to weighing bottles . The latter were all

closed within 4 minutes after the sample bottles were first

opened } and were weighed within the next hour. The No. 1 3 2_} 7 } and 8 samples , weighing 7 to 10 g each (in 5- to 7-mm deep

layers) were in 40- x 50-mm weighing bottles; the other samples s weighing approximately 1.5 g each^ were in 25- x 40-mm weighing

bottles

The No. 1 and 7 samples were dried under usual Washington

laboratory conditions : with the moisture of the ambient autumn

air varying from 0.010 to 0.003 g H

2 0/g dry air.* The No. 2 and 8_ samples were dried in a specially conditioned room with

the moisture of the ambient air maintained at approximately

0.013 g/g (or 80°F and "60" percent relative humidity) to simulate a Florida atmosphere. The No. 3 and 5_ samples were assayed.

The No. 4 and 6_ samples were stored in closed weighing bottles

(but not in a desiccator) in the laboratory for 39 days,, and

then were used to test experimental procedures before application of the latter to the No. _1 and 2_ samples. Figure 1 shows

#- The wet and dry bulb temperatures were obtained at the end

of each drying interval with a Weather Bureau sling psychrometer, and the measurements were converted to g of moisture

per g of dry air with the aid of a psychrometric chart.

81
2.00 —

.00 -

O VARIABLE HUMIDITY

(AS INDICATED) • CONSTANT HUMIDITY

(.OI3gH 2 0/g DRY AIR) .003

1.00

LOT

4

5 -

2.00

1.00 -

Figure 1. NBS results for drying IMCC material in room air.

the variations in loss results due to varying the moisture of

the ambient air from 0.013 to 0.003 g/g. In order to determine how much the loss values could be

increased by reducing the moisture content of the air, the

No. 1, 2, and 4 samples were later dried in a smaller oven

(3.7-liter capacity) through which air from a silica gelAnhydrone drying train was blown in at a rate of 200 to 250 ml

per minute . As shown in figure 2 S (1) loss values increased

as much as 0 o 8 percent over the previous ones (figure 1),

(2) constant weights were not reached in 160 hours^ but (3) lar^ 82
Figure 2. NBS results for drying pre-treated IMCC

material in "dry" air.

83
amounts of moisture absorbed during exposure of the No. 2 and 4 samples to room atmospheres were removed rapidly (within 24

hours )

.

Observations were made on the absorption of moisture by

samples that were kept at room temperature under various atmospheres. In closed weighing bottles , gains were negligible in

19 hours for the dried No. 1 and 2 samples during storage in

air containing 0.003 g H

2 0/g dry air, but amounted to about

1 percent within 40 days for the "as is" No. 4 and 6 samples

during storage in air containing 0.004 to 0.013 g H

2 0/g dry air.

In open weighing bottles in air containing 0.013 g H

20/g dry

air, the No. 1, 2, and 4 samples of each lot gained as fast

as 0.3 percent per hour and up to a total of 2 or 3 percent.

Finally, after redrying the No. 2 and 4 samples, the No. 1,

_2, and 4 samples were heated at 110°C in a controlled, humid

atmosphere obtained by passing air containing approximately

0.013 g H

2 0/g dry air through the small (3.7-liter) oven at a rate of 130 to 220 ml/minute.* The results are shown in figure 3. All samples came to constant weight within 5 hours, and

both wetter (No. 1_) and drier (No. 2 and 4) samples approached

the same equilibrium values. For the No. 2 samples, the final

weights were the same as those (figure 1) originally obtained

by drying in a gravity-convection Iso-Temp oven in a room with

^. Before entering the oven, the air was equilibrated with a saturated NH4NO3 - H2O mixture at 24 to 28 °C . The same results were obtained by simply passing the air over the

mixture as by bubbling it through a series of saturated

NH4NO3 solutions.

84
2 «— SAMPLE NO.

2.00

1.00

S

i-oo [

o I 2.00

1.00 r

20

•• •

LOT4

20 40 0 HOURS AT IIO°C 20 40

Figure 3. NBS results for heating pre-treated IMCC

material in humid air (about 0.01J> g HpO/g

dry air)

.

a controlled atmosphere (0 o 013 g E^O/g air). The final loss

values for the No. 1 and 4 samples were similar to those for

the No. 2 samples even though the former may have undergone

physical changes during the prolonged dry air treatment of the

No. 1 samples and the prolonged "wetting" of the No. 4 ' s (the

wetting caused etching of the weighing bottles)

In the case of Lot 5, etching was observed only with the

samples that were allowed to absorb considerable moisture

(No. 4 and 6_ samples). But for Lots 4 and 6, even the drier

samples (No. 1_, 2, J_ and 8) eventually produced interference

rings in their weighing bottles. Lot 6 gave the most etching and Lot 4 gave almost as much.

85
The results shown in figures 1 and 3 indicate that IMCC

material was readily dried to a reproducible state in an atmosphere containing about 0,015 g HgO/g dry air.

On the basis of this study and the interlaboratory com- parison of IMCC, NBL, and NBS results for Lots 4, 5, and 6, it was suggested in 1957 that for IMCC material:

(1) All analytical samples be taken and weighed promptly

after the initial opening of the sealed bottle.

(2) Loss determinations be made on approximately 10-g

samples in weighing bottles 40 mm in diameter.

(5) All laboratories determine losses under the same at- mospheric moisture conditions (e 0 g 0 0.011 to 0.014 g HgO/g dry

air) 0 (4) The samples be dried at 110°C in the laboratories for

only two short (4-or 5- hour) intervals, since the purpose of

the drying in the laboratory was to remove only the moisture

absorbed after the sampling plant dry-weight basis had been

established. One drying interval probably would suffice if a mechanical-convection type oven were used, but two drying

periods might be needed with a gravity-convection oven.

(5) Any samples bottled at the sampling plant in humid

weather be examined for possible side effects, because of the

likelihood of hydrogen fluoride liberation during storage.

8 b
APPENDIX D Summary of NBS Drying Studies of Four Lots of Blockson

Uranium Concentrates

Because of the extremely hygroscopic nature of Blockson

uranium phosphate material; these studies were made in 1959 at NBS to determine the amount and rate of loss at 110 °c of the

Blockson material in bone-dry air and to identify the variables

to be controlled in order to obtain reproducible results.

Description of Drying Train for Obtaining Bone-Dry Air

Compressed air was passed at a rate of 1.0 to 1.3 liters

per minute through a drying train arranged as follows:

(1) Column of absorbent cotton

(2) Two or more columns of indicating silica gel,,

reactivated by heating at 110 °C to 180 °C . The first column

contained about 150 g of silica gel and was reactivated daily. No color change was observed in the second column . (3) Trap

(4) T-tube dipping in mercury. The tube containing

the mercury was supported in an extra container and loosely

covered so as to prevent accidental scattering of mercury.

(5) Trap

(6) Shepherd trap immersed in a. dry-ice-acetone

slurry (about -77°C) contained in a four-liter Dewar tube.

The Shepherd trap was the concentrating sampler described by

87
M. Shepherd et al*. The main tube was 260--mm high and 40 mm

in diameter. The glass wool filter was 60- mm high and about

3 mm thick. In the set-up for uranium concentrate studies,

air entered the outside tube and left through the center.

(7) Glass connecting tube, 9 nim in diameter and

60 cm long.

(8) Rotameter tube (Brooks Tru-Taper Tube Size 2-15-3,

with stainless steel float).

(9) Glass and saran connecting tubes.

(10) Oven, 3.7-liter capacity, with an all-metal,

hermetic lining and an entry port loosely covered with a piece

of metal to disperse the entering air stream. The oven was designed for vacuum drying, but in this case was used at atmospheric pressure with air escaping only around the door, which

was held in place by springs. (Slight additional pressure on the door decreased the rotameter reading momentarily. ) There were no rubber or plastic connections between the Shepherd trap

and the oven. General Procedure

(a) Sampling. The material was grab-sampled as described

in the basic procedure given in the text, sections 4.C.la and

4.C.1C.

(b) Drying. From two to five weighing bottles, including

a tare, were placed in the dry air oven together. The caps were tilted on the bottles during drying and all of the bottles

Shepherd, M. , Rock, S. M. , Howard, R. , Stormes, J., Anal.

Chem. 23, 1431-33 (1951).

88
were closed as rapidly as possible after the oven was opened.

Then all of the bottles were transferred to a l60-mm desiccator

freshly charged with magnesium perchlorate or phosphorus pentoxide. After cooling for one hour., each cap was loosened for an instant and closed . firmly . The closed bottles were left in

the desiccator for at least an additional half-hour before

weighing, against the tare. Experimental and Results

(a) Study No. I. Initial tests were made on Lots II-58

and 12-58 as follows:

(1) The drying was repeated until less than 0.05

percent loss was obtained in each of two 20-hour intervals.

The maximum loss was obtained after a total of 72 hours.

(2) Then the dry ice (in part 6 of the drying train)

was omitted for two drying intervals. This resulted in a gain

of 0.07 percent when the silica gel was reactivated at 110°C 3 and a return to the maximum loss when the silica gel was reactivated at 170°C in a relatively dry ambient atmosphere.

(b) Study No. II. Supplementary tests were made on Lots 2-59 and 5-59- When the bottles were first opened on 8-28-59, the materials were grab-sampled as usual, except that

a total of seven samples from each lot were taken as follows:

The first two and last two samples (No. A, B, F, and G) of

each lot weighed 4.5 to 7.2 g and the middle three samples

(No. _c, _d, and ej weighed approximately 1.5 g each. The

following precautions regarding drying were observed. The

89

790-939 0-65—

7
silica gel in the first drying column was replaced daily; it was reactivated by heating overnight at approximately 175°C.

One dry-air apparatus was used for all dry-air tests. The

Shepherd trap was left in the train even when the trap was not

cooled; but before use at room temperature 3 it was flushed with

dry air enough to insure that its interior was dry. Whenever

the air flow was discontinued, as during the replacing and

cooling of silica gel, the exit of the Shepherd trap was closed.

Except in test 5, all dry-air samples were heated in groups of two or three and cooled in covered weighing bottles beside a fresh portion (three inches in diameter) of phosphorus pentoxide

in a l60-mm desiccator. Seven tests were made as follows:

(1) One sample (A or B) of each lot was heated for

three intervals totaling 70 hours, in silica-gel-dried air.

(2) After test 1 was completed, -the duplicate

samples (A or _B) were heated in silica-gel- plus cold-trapdried air for three intervals totaling 68 hours.

(3) While samples A and B_ were heated in dry air.,

samples F_ were heated in normal air for seven intervals

totaling 148 hours.

(4) Samples _e were stored in a covered plastic box

at room temperature for 2 weeks.

(5) Samples _e and _F of both lots were heated

together in silica-gel-dried air for l4 hours.

(6) Samples and G, of Loi: 2-59 were heated in

silica-gel-dried air for four intervals totaling 91 hours.

90
(7) Samples e__, _F 3 and Cr of Lot 3-59 were heated

together in silica-gel-dried air for 4 intervals totaling 93

hours. The samples in test 7 were heated every other night

and those in test 6 were heated on the alternate nights.

The results are summarized in table 1. The duplicate

results obtained for the A and B samples (tests 1 and 2) and

later confirmed with the G- samples (tests 6 and 7) showed that

the cold trap can be omitted when the air_, containing up to

Table 1„ Changes in weight of Blockson samples during heating

at 110 °C in varied atmospheres, and during storage.

Conditions Percent Change in Weight

Test Air Time Lot 2-59 Sample Lot 3-59 Sample

No. Treatment (hr) it "A" a F e

1 Silica gel^ 70 -0 .62° -0.83°

2 Cold trap*

3 68 -0 .63

C -0.85°

3 Untreated^ Untreated

131 148 +1.77°

+ 1.60

+ 1 + 1 .96°

.85

4 None 330 - d

+ 2.7

C + 2.4°

5 Silica gel^ 14 +0.18 +0.3 -0 . 14 -0.3

6 Silica gel^

Silica gel

73

91

-0

-0 .66°

.67 -0.43 -0.7, -0.48 '°- 7 3

7 Silica gel^

Silica gel

61

93 -0.89°

-0.94

-0

-0 .72

.82

-°' 9 4

This column includes results for A, B, and G samples: A was used for tests 1 or 2; B, for the other; and G, for 6 or 7

.

Followed by heating at 110 °C, for one or more overnight intervals.

^ Result is for initial test of this sample. Dash indicates omission of sample from test. 91
0.015 g HgO/g dry air (62 percent relative humidity at 83 °F)

is dried with silica gel reactivated at 175°C

Increasing the sample depth by 6 mm or opening the weighing bottle for 1 minute in normal air containing 0.011 g H

2 0/g

dry air appeared to decrease the loss by less than 0.1 percent.

Comparison of results for _F 3 and Cr samples indicate

that samples heated at 110 °C in normal air absorb moisture

that is more difficult to remove than that absorbed at room

temperature. However., the difference was less than 0.3 percent

after 73 hours in dry air., and appeared to slowly decrease with

additional drying. It seems plausible that the alternate heating and cooling of the _F samples in normal air (for 7 intervals)

would cause the ambient water vapor to penetrate more deeply

into the sample particles and thus make it more difficult to remove.

92
7. ACKNOWLEDGMENT

This report concerns work done on behalf of the U. S. Atomic Energy Commission and performed by many employees of

NBS 3 with the cooperation of many others of the AEC and its

contractors. Special appreciation is expressed for the years

of guidance from H. A. Bright and J. L. Hague in the laboratory 3 and for the assistance of 0. Menis, W. J. Youden 3 and

R. S. Maddock in the preparation of this report.

93
8 . REFERENCES

[1] Smyth, H. D, , "A General Account of the Development of

Methods of Using Atomic Energy for Military Purposes

Under the Auspices of the United States Government

1940-1945 "* pp. 48,, 65-8 # Superintendent of Documents,,

Washington, D. C. (1945).

[2] Steele, T. W. , Taverner, L., "Report of Calcining Tests

on Samples of Dried Calcined Uranium Precipitates as Prepared by Calcined Products (Proprietary) Limited "5 Gov't Metallurgical Laboratory, Johannesburg,

S. Africa, Analytical Progress Rept. No, 21 , 15 pp. (1953).

[3] Rodden, C. J., Proc. Intern. Conf. Peaceful Uses Atomic

Energy, Geneva, 1955 , 197-205 (1956).

[4] Valent, D. , Gessiness, B. , "The Effect of the Moisture

Determination on the Assay of Uranium Ore Concentrates", National Lead Company of Ohio, in U.S. Atomic

Energy Commission Rept. TID-7541 (Pt. 2) , 31-42 (1957).

[4-b ] Langridge, R. W. , "Evaluation of the Purchase Method for

the Sampling and Analyzing of Uranium Concentrates

at Grand Junction", Lucius Pitkin, Inc., in U. S. Atomic Energy Commission Rept. TID-7581 , 85-115 (1959).

[5] Nelson, S. D., Kneip, T. J., Mohl, A. H., U. S. Atomic

Energy Commission Rept. MCW-1455 (1962).

94
[6] Roszkowski, E. S., Mullin, H. R., Lanza, R. J., U. S. Atomic Energy Commission Repts. NBL-I76 , NBL-187 , NBL-203 , NBL-221 (1961-1964).

[7] Furman, N. H. , Mason, W. B., Pekola, J. S 0 Anal.

Chem. 21, 1325-1330 (1949).

[8] Grimaldi, F G S., in U. S. Geological Survey Bulletin

1006 , 37-^1 (1954).

[9] Sill, C. W., Peterson, H 0 E., Anal. Chem. 24, 1175-82,

1455 (1952).

[10] Rodden, C. J., Analysis of Essential Nuclear Reactor

Materials , C. J. Rodden, ed., 1-157; U. S. Atomic

Energy Commission, Superintendent of Documents,

Washington, D. C. (1964).

[ll] Steele, T. ¥., Taverner, L., Proc . 2nd Intern. Conf.

Peaceful Uses Atomic Energy, Geneva, 1958 , 3j 510-26

(1958).

[12] Booman, G. L., Rein, J 0 E., Treatise on Analytical

Chemistry , I. M. Kolthoff and P. J. Elving, eds.,

Part II, Vol, 9, 1-188, Interscience, New York, 1962.

[l33 Jones, R. J., ed., Selected Measurement Methods for

Plutonium and Uranium in the Nuclear Fuel Cycle , U. S. Atomic Energy Commission Rept . TID-7029 , 49-50,

96-107 (1963).

95
[l4] Mallinckrodt Chemical Works , Uranium Division Weldon

Spring, Mo . , "Uranium Assay of Ore Concentrate "

17 pp. (February 25 , 1963)

[15] Langridge, R. W. , Bush, ¥. E., Higgins, L. J. , Williams

C 0 W.j "Handbook of Analytical Procedures/' U. S. Atomic Energy Commission Rept. RMO-^001 Rev. No. 1 , 48-52 (196l) 0 [l6] Swift , E 0 Ho j Anson, F. C. , Advances in Analytical

Chemistry and Instrumentation , C. N. Reilley, ed.,

Vol. 1, 293-345 } Interscience, New York, i960.

[17] Rowe, J 0 J., in U t S. Geological Survey Bulletin 1006 , 121-24 (1954).

[l8] Branham, J. R., Sperling, E. 0., NBS J. Research 22_, 701-05 (1939).

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Dear Sir: Please add my name to the announcement list of new

publications to be issued in the series: NBS Miscellaneous

Publication 260 - Standard Reference Materials.

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