NUREG/CR-6632 

 PNNL-12205

 

Solubility and Leaching of

Radionuclides in Site

Decommissioning

Management Plan 

(SDMP) Slags

Pacific Northwest National Laboratory

 U.S. Nuclear Regulatory Commission

Office of Nuclear Regulatory Research

Washington, DC 20555-0001
 

 

NUREG/CR-6632 

PNNL-12205

Solubility and Leaching of

Radionuclides in Site

Decommissioning

Management Plan

(SDMP) Slags

Manuscript Completed: September 2001 

Date Published: February 2002

Prepared by

A. R. Felmy, D. Rai, S. A. Hartley,

V. L. LeGore 

Pacific Northwest National Laboratory

Richland, WA 99352

P. Reed, NRC Project Manager

Prepared for

Division of Systems Analysis and Regulatory Effectiveness

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

NRC Job Code W6409

ii
ABSTRACT

Samples of disposed wastes at three U.S. 

Nuclear Regulatory Commission (NRC) Site 

Decommissioning Management Plan 

(SDMP) sites were studied to determine 1) 

the key radionuclides and their 

concentrations present in the waste, 2) the 

solubility limits and solubility limiting 

phases for these radionuclides, 3) the rate of 

attainment of solubility equilibrium, 4) the 

observed leaching rate for radionuclides 

which may or may not be solubility 

controlled, and 5) the potential for 

radiocolloid formation. In order to achieve 

these goals batch studies of ground or 

fractured samples were conducted over 

ranges of solution pH values (2 - 12), solid 

to solution ratio, and particle size. In 

addition, flow-through column studies were 

conducted of selected samples to help verify 

the mechanisms and predictive relations 

identified in the batch experiments. Three 

slag containing sites were selected for study. 

The results for slags at all three sites show 

that the major radionuclides present in the 

wastes were Th and U with their associated 

daughter products. Th daughters were in 

secular equilibrium with the parent Th-232 

in all samples. U-238 daughters were in 

secular equilibrium in certain highly 

solidified non-porous samples but escape of 

Rn-222 had occurred from more porous 

samples perturbing the U-238 secular 

equilibrium. Analysis of solution phase 

concentrations and solid phase composition 

indicated that aqueous Th concentrations are 

solubility controlled, most likely by 

thoranite, ThO2(c), which sets an upper limit 

on the dissolved Th concentrations. 

Uranium also appears to be solubility 

controlled in certain waste samples 

(thoriated slags) high in pH and alkaline 

earth cations (Ca, Sr, Ba), upper limits on 

the observed solubilities apparently being 

set by the secondary formation of alkaline 

earth uranates. Comparisons of filtered and 

unfiltered analyses of samples from flowthrough columns did not show any evidence 

for the presence of radiocolloids. Maximum

dissolved concentrations (solubility limits) 

and radionuclide leaching rates have been 

calculated for three sites for use in 

performance assessment calculations. 

Observed Th and U solubilities were quite 

low (maximum Th solubilities of 3.2x10-8

M, 4x10-8 M, and 3.2x10-9; maximum U

solubilities were 2.5x10-8 M, 6.3x10-8 M, 

and 8.9x10-9M all for sites A, B, and C 

respectively). Observed leaching rates for 

the three sites were 100, 1 and 0.2 pCi/yr for 

Th and 260, 8 and 2 pCi/yr for U again for 

sites A, B, and C respectively. Chemical 

modeling of well water compositions at site 

C indicates that the low concentrations of 

soluble uranium are primarily present as 

anionic uranium carbonate complexes. 

Statistical analysis of the batch, column, and 

solubility data showed that the uncertainties 

in the dissolved Th and U concentrations 

can be described using a lognormal 

distribution with a meanlog of –17.7 and a 

sdlog of 0.57 for U and a meanlog of –19.5 

and an sdlog of 1.7 for Th. These 

parameters are valid for all three sites.

iii
iv
CONTENTS

ABSTRACT...................................................................................................................................iii 

CONTENTS.................................................................................................................................... v 

FIGURES...................................................................................................................................... vii 

TABLES ......................................................................................................................................viii 

EXECUTIVE SUMMARY ........................................................................................................... xi 

FOREWORD...............................................................................................................................xiii 

LIST OF ABBREVIATIONS....................................................................................................... xv 

1 INTRODUCTION ...................................................................................................................... 1 

2 SITE SAMPLING AND SAMPLE SELECTION ..................................................................... 3 

3 METHODS AND MATERIALS................................................................................................ 5 

3.1 Chemical Analysis Procedures ............................................................................................ 7 

3.2 Radiological Analysis.......................................................................................................... 7 

3.3 Solubility and Batch Studies................................................................................................ 7 

3.4 Column Studies.................................................................................................................... 8 

4 RESULTS AND DISCUSSION............................................................................................... 11 

4.1 Chemical Analysis............................................................................................................. 11 

4.2 Radiological Analysis........................................................................................................ 19 

4.3 Solubility and Leaching Studies ........................................................................................ 24 

4.3.1 Site A .......................................................................................................................... 24 

4.3.1.1 THORIUM........................................................................................................... 24 

4.3.1.2 URANIUM .......................................................................................................... 27 

4.3.1.3 OTHER RADIONUCLIDES............................................................................... 30 

4.3.2 Site B........................................................................................................................... 30 

4.3.2.1 THORIUM........................................................................................................... 30 

4.3.2.2 URANIUM .......................................................................................................... 32 

4.3.2.3 OTHER RADIONUCLIDES............................................................................... 35 

4.3.3 Site C........................................................................................................................... 35 

4.3.3.1 THORIUM........................................................................................................... 35 

4.3.3.2 URANIUM .......................................................................................................... 37 

v
5 CALCULATIONS OF SOLUBILITY LIMITS AND LEACHING RATES.......................... 39 

5.1 Site A ................................................................................................................................. 39 

5.2 Site B.................................................................................................................................. 39 

5.3 Site C.................................................................................................................................. 39 

6. COLLOID STUDIES................................................................................................................ 41 

7 STATISTICAL ANALYSIS .................................................................................................... 43 

7.1 Batch Studies (Sites A and B)............................................................................................ 43 

7.2 Column Studies (Sites A and B)........................................................................................ 47 

7.3 Solubility Data (Sites A and B) ......................................................................................... 48

7.4 Site C Comparison ............................................................................................................. 49 

Appendix A: Earlier Studies of Site C Samples ........................................................................ A-1 

Appendix B: Tables of Experimental Data................................................................................ B-1 

Appendix C: Thermodynamics of the U(VI)-Ca2+-Cl-

-OH--H2O System: Solubility Product 

 of Becquerelite ......................................................................................................C-1 

vi
FIGURES 

Figure 3-1. Schematic outline of sample treatment and analysis................................................... 6 

Figure 3-2. Schematic of Column Apparatus. The designation “soil” represents soil or slag 

depending upon the specific sample. The pH port, which was present on only a few 

columns, was not used. All pH measurements were made in the sample collecting vessel. . 9 

Figure 4-1. Calculated uranium species distribution for well #10 as a function of pH at site C. 

Anionic uranium complexes are the dominant species at the pH of the well sample, 6.8.... 18 

Figure 4-2. Example Alpha Spectra of Site A samples. .............................................................. 23 

Figure 4-3. Example Alpha Spectra of Site B samples................................................................ 23 

Figure 4-4. Th concentrations in Site A Solubility Studies. ........................................................ 25 

Figure 4-5. Th concentrations in Site A Batch Leaching Studies................................................ 25 

Figure 4-6. Th and U concentrations in Site A Column Studies. ................................................ 26 

Figure 4-7. Alkaline Earth Cation Solubilities in Site A Samples............................................... 28 

Figure 4-8. Aqueous uranium concentrations contacting becquerelite suspensions in 0.1M CaCl2

and over a range of hydrogen ion concentrations (pCH+ values). The designation (mol/dm–3) 

is equivalent to moles/l. See Appendix C for a detailed explanation. ................................. 29 

Figure 4-9. U concentrations in Site A Solubility Studies. The calculated becquerilite values use 

thermodynamic data taken from Grenthe et al. (1992), see Appendix C. ............................ 29 

Figure 4-10. U concentrations in Site A Batch Leaching Studies. The area designated for the 

solubility study values represents the range of observed concentrations. ............................ 30 

Figure 4-11. Th concentrations in Site B Solubility Studies. ...................................................... 31 

Figure 4-12. Th concentrations in Site B Batch Leaching Studies.............................................. 33 

Figure 4-13. Th and U concentrations in Site B Column Studies................................................ 33 

Figure 4-14. U concentrations in Site B Solubility Studies......................................................... 34 

Figure 4-15. Calcium concentrations in Site A and Site B Solubility Studies. ........................... 34 

Figure 4-16. U concentrations in Site B Batch Leaching Studies................................................ 35 

vii
Figure 4-17. Thorium concentrations in Site C Solubility Studies.............................................. 36 

Figure 4-18. Thorium and uranium concentrations in Site C Column Studies............................ 37 

Figure 4-19. Uranium concentrations in Site C Solubility Studies.............................................. 38 

Figure 7-1. Distributions of batch data for Th and U (moles/l). (a) Site B U. (b) Site B Th. (c) 

Site A U. (d) Site A Th. ........................................................................................................ 43 

Figure 7-2. Actual (a) and hypothesized (b) distributions of U concentrations (M) in batch 

experiments at site B............................................................................................................. 44 

Figure 7-3. Actual (a) and hypothesized (b) distributions of Th concentrations (M) in batch 

experiments at site B............................................................................................................. 45 

Figure 7-4. Actual (a) and hypothesized (b) distributions of U (M) concentrations in batch 

experiments at site A............................................................................................................. 46 

Figure 7-5. Actual (a) and hypothesized (b) distributions of Th concentrations (M) in batch 

experiments at site A............................................................................................................. 47 

Figure 7-6. Comparisons between site A and B batch and column data for Th and U. The 

darkened points are the column study data, while the clear points represent the batch data. 

(a) Site B uranium. (b) Site B thorium. (c) Site A uranium. (d) Site A thorium. ................. 48 

Figure 7-7. Comparisons between site A and B combined batch and column data with solubility 

data (pH 7-10) for Th and U. The darkened points are the batch and column study data, 

while the clear points represent the solubility data. (a) Site B uranium. (b) Site B thorium. 

(c) Site A uranium. (d) Site A thorium. ................................................................................ 49 

Figure 7-8. Comparisons between solubility and column data at Site C. (E) Thorium solubility 

data, (F) Thorium column data, (G) Uranium solubility data, (H) Uranium column data. .. 50 

Figure 7-9. Comparisons between the column and solubility data at Site C. (EF) Thorium data, 

(GH) column data. ................................................................................................................ 51 

TABLES 

Table 4-1. Chemical composition of slags at Site A.................................................................... 13 

Table 4-2. Chemical composition of samples collected at Site B................................................ 14 

Table 4-3. Chemical composition of slag samples 1 and 2 at Site C........................................... 15 

Table 4-4. Minerals present at sites A, B, and C (Veblen et al. 2000). ....................................... 16 

viii
Table 4-5. Chemical analysis of filtered water and well samples at Site C. Field data supplied 

by SCIENTECH Inc. DO represents dissolved oxygen. Concentrations in mg/l, pH in 

units. Inorganic carbon (IC) in mg/l as C. Alkalinity is reported as mg/l as CaCO3 with the 

value in parentheses converted to mg/l as C for comparison with the IC analysis............... 16 

Table 4-6. Chemical analysis of unfiltered water and well samples at Site C. Concentrations in 

mg/l, pH in units. Values in parentheses are the corresponding values for filtered samples 

to assist in distinguishing the chemical composition of the solids in the samples. .............. 18 

Table 4-7. Radiological analysis of slags at Site A. All analyses represent the average of three 

subsamples of each slag. Values in pCi/g............................................................................ 20 

Table 4-8. Radiological analysis of Site B samples. Slag A(96T-C-9),Grayish Green Ore(96TC-19), Soil Site B5(96T-C-20), and Ore (96T-C-21). Results in pCi/g. ............................. 21 

Table 4-9. Radiological analysis of Site C samples. Results in pCi/g........................................ 22 

Table 4-10. Uranium and thorium isotopic analyses of selected samples. Results in pCi/g. ...... 22 

Table 4-11. Measured pH values in batch leaching studies as a function of time....................... 26 

Table 4-12. pH values measured in batch studies exposed to atmospheric CO2. ........................ 27 

Table 4-13. Measured pH values in column studies as a function of time. ................................. 27 

Table 4-14. Measured pH values and Ca concentrations in batch leaching studies as a function 

of time for Site B samples..................................................................................................... 32 

Table 4-15. pH values in column studies from slags at Site C. ................................................... 37 

Table 5-1. Summary of Solubility and Leaching Rate Calculations at each Site........................ 40 

Table 6-1. Filtered and unfiltered Th and U concentrations in column studies. UF - unfiltered, 

F - filtered. Pore size of filters approximately 0.0018um..................................................... 41 

ix
x
EXECUTIVE SUMMARY 

Each year the NRC receives requests to 

discontinue licensed operations that involve 

the use of radioactive materials (NRC 1993). 

However, the termination of some licenses 

and the possible release of the site for 

unrestricted or other uses are sometimes 

non-routine owing to the level, volume, or 

complex nature of the radiological 

contamination. In such cases a more clear 

scientific understanding of the nature, both 

physical and chemical, of the radiological 

contamination is required to make informed 

judgments as to the level of site remediation 

that may be required. As part of such an 

overall effort this report summarizes the 

findings from solubility, batch, and 

soil/waste column studies conducted on 

wastes from three NRC Site 

Decommissioning Management Plan 

(SDMP) sites. These studies were designed 

to determine 1) the key radionuclides and 

their concentrations present in the waste, 2) 

the solubility limits and solubility limiting 

phases for these radionuclides, 3) the rate of 

attainment of solubility equilibrium, 4) the 

observed leaching rate for radionuclides 

which may or may not be solubility 

controlled, and 5) identify, if possible, the 

potential for radiocolloid formation. Three 

sites were selected for study, labeled Sites 

A, B, and C, which provided a range of 

materials for analysis that covered different 

processing conditions and represented 

differences in chemical and physical 

properties of the slags. The results for all 

three sites showed that the major 

radionuclides present in the wastes were Th 

and U with their associated daughter 

products. Analysis of solution phase 

concentrations and solid phase composition 

indicated that aqueous Th concentrations are 

solubility controlled, most likely by 

thoranite, ThO2(c), which sets an upper limit 

on the dissolved Th concentrations. U also 

appears to be solubility controlled in certain 

waste samples (thoriated slags). 

Comparisons of filtered and unfiltered 

analyses of samples from flow-through 

columns did not show any evidence for the 

presence of radiocolloids. Maximum 

dissolved concentrations (solubility limits) 

and radionuclide leaching rates have been 

calculated for use in performance 

assessment calculations. Observed Th and 

U solubilities were quite low (maximum Th 

solubilities of 3.2x10-8 M, 4x10-8 M, and 

3.2x10-9 M; maximum U solubilities were 

2.5x10-8 M, 6.3x10-8 M, and 8.9x10-9 M all 

for sites A, B, and C respectively). 

Observed leaching rates for the three sites 

were 100, 1 and 0.2 pCi/yr for Th and 260, 8 

and 2 pCi/yr for U again for sites A, B, and 

C respectively. Chemical modeling of well 

water compositions at site C indicates that 

the low concentrations of soluble uranium

are primarily present as anionic uranium

carbonate complexes. Statistical analysis of 

the batch, column, and solubility data 

showed that the uncertainties in the 

dissolved Th and U concentrations can be 

described using a lognormal distribution 

with a meanlog of –17.7 and a sdlog of 0.57 

for U and a meanlog of –19.5 and an sdlog 

of 1.7 for Th. These parameters are valid 

for all three sites. These results thus provide 

experimental evidence of the nature of the 

contamination present at these sites and the 

range of conditions under which the 

radionuclides are likely to be either soluble 

and mobile in the groundwater or insoluble 

and immobile. It is anticipated that such 

results will assist in the evaluation of 

effective remediation strategies for these 

sites. 

xi
xii
FOREWORD 

xiii
xiv
LIST OF ABBREVIATIONS 

Ac Actinium

(am) amorphous 

Al Aluminum

BET Brunauer-Emmett-Teller 

Bi Bismuth 

( c ) crystalline 

Ca Calcium

Ci/ml Curies per milliliter 

DU Depleted Uranium

EDXRF Energy dispersive x-ray fluorescence 

Fe Iron 

g gram

(gl) glass

GM Gieger-Müller 

IC Ion Chromatograph 

ICP Inductively coupled plasma spectroscopy 

ICP-MS Inductively coupled plasma mass spectrometry 

kev one thousand electron volts 

kgs kilograms 

m meter

mg/l milligrams per liter 

ml milliliter

mm millimeter 

M molarity (moles/l) 

Mo Molybdenum 

Nb Niobium

NRC United States Nuclear Regulatory Commission 

ORISE Oak Ridge Institute for Science and Education 

Pb Lead

PCi/g picocuries per gram

PCi/yr picocuries per year 

pH Negative log of the activity of H+ 

PNNL Pacific Northwest National Laboratory 

ppm parts per million 

Ra Radium

Rn Radon 

SDMP Site Decommissioning Management Plan 

Si Silicon 

Ta Tantalum

Th Thorium

U Uranium

XRF X-ray fluorescence 

xv
xvi
Introduction 

1 INTRODUCTION 

The U.S. Nuclear Regulatory Commission 

(NRC) has identified 51 sites around the 

U.S. that have radionuclide contamination 

that exceeds NRC criteria for unrestricted 

use (NRC 1995). All of these sites require 

some degree of remediation before sites can 

be released for unrestricted use. One of the 

principal types of contaminants present at 

these sites is thoriated slags produced as 

byproducts from processing ferrocolumbium

alloys or tin slag. The thoriated slags were 

then mixed with site material (i.e. soils, 

building rubble, or other wastes) and 

disposed either in unlined slag piles, over 

embankments, or by other means (NRC 

1995). As a result, the NRC is currently in 

the process of conducting performance 

assessments of these sites to better ascertain 

the potential for radionuclides solubilization, 

leaching or migrate off site. As part of this 

overall effort, the Pacific Northwest 

National Laboratory (PNNL) was contracted 

to obtain selected samples from different 

SDMP sites and conduct batch and flowthrough column leaching studies of these 

wastes to determine the radionuclides 

present in the waste, the maximum leachable 

concentrations (solubility limits) for 

important radionuclides, the time required 

for radionuclides to reach solubility 

equilibrium, the overall radionuclide 

leaching rates, and, if possible, identify the 

potential impact of colloids in transporting 

radionuclides. 

This report presents detailed results of 

PNNL studies on three selected SDMP sites, 

which represent a range of slag 

compositions and disposal practices. 

Disposal practices ranged from gathering the 

waste materials and placing into barrels or a 

slag pile (site A) to direct disposal over 

embankments (site B) or a combination of 

such practices (site C). The radionuclide 

containing wastes at these sites are 

principally thoriated slags produced from

processing tin slag or ferrocolumbium 

alloys. The following sections of this report 

describe site sampling and sample selection, 

chemical analysis, radiological analysis, 

solubility and leaching studies, and 

investigations of radiocolloids. 

1
Introduction 

2
Site Sampling and Sample Selection 

2 SITE SAMPLING AND SAMPLE SELECTION 

Samples from Site A were sent to PNNL 

following a visit to the site. Four samples of

the disposed slags with the highest 

radionuclide content (>1000pCi/g) in the 

slag pile were obtained. All of the samples 

were large pieces ( ~1-1.5kgs)of grayish 

slag with a rust and white coating. The 

samples from Site B were obtained by both 

PNNL and NRC staff from diggings near the 

edge of the embankment. A total of 21 

samples from Site B were obtained and 

shipped to PNNL. Preliminary gamma 

scans were performed on all samples and 

three of the samples with the highest 

radioactivity were selected for detailed 

study. These samples were 1) 2 kgs of slag 

pieces mixed with some soil (sample C-9), 

2) a relatively small (280g) grayish green 

sample of slag/ore (sample C-19), and 3) 1 

kg of sandy soil mixed with pieces of slag 

(sample C-20). 

PNNL received two sets of samples from

Site C. The first set was collected by staff at 

the Center for Nuclear Waste Regulatory 

Analyses (CNWRA), San Antonio TX and 

sent to PNNL for analysis. Only a limited 

amount of radiological and chemical 

analyses were performed on these samples 

owing to the small size of the samples. 

Many of these samples were nonradioactive. Appendix A presents a 

complete description of these samples and 

the analyses conducted by PNNL. A second 

set of samples was then collected by NRC, 

Commonwealth of Pennsylvania, and 

SCIENTECH, Inc. staff at site C in 2001 

and shipped to PNNL for more detailed 

analysis. These samples consisted of six 

well water or river water samples and two 

samples of slag. All of the well water 

samples contained suspended or particulate 

material of a brownish to rust color upon 

arrival. As a result the samples were filtered 

to remove solids and determine dissolved 

concentrations. Both the unfiltered and 

filtered samples were analyzed.

 

3
Site Sampling and Sample Selection 

4
Methods and Materials 

3 METHODS AND MATERIALS 

The presence of a solubility controlling solid 

phase in a soil or slag sample means that the 

radionuclide concentration in equilibrium

with this phase will vary only with the 

chemistry of the water in contact with the 

soil or sediment and will be independent of 

time, particle size, and solid to solution 

ratio. Therefore, all of these factors must be 

varied in the experimental design in order to 

establish that a solubility controlling phase 

is present. The experimental design outlined 

here attempts to accomplish these goals by 

1) conducting studies as a function of water 

chemistry (pH, CO2 content), 2) conducting 

long term studies with both coarse and fine 

material to test the independence of particle 

size, and 3) conducting studies at different 

solid to solution ratios. In the latter case we 

chose to conduct studies at high solid to 

solution ratio and these studies were most 

easily done by using flow through columns. 

The column studies also allow insight to be 

gained into the rate of the reactions. It is 

often difficult to vary the chemistry 

(particularly the pH) of the samples at high 

solid to solution ratio since large 

concentrations of acid or base must be 

added. Therefore the pH varying studies 

(labeled “solubility” henceforth) were 

conducted at low solid to solution ratios and 

using fine material to enhance the reaction 

rate. The other studies that were conducted 

were done at low solid to solution ratio 

without the addition of acid or base. These 

studies were done wherever possible using 

both fine and coarse material to evaluate the 

possible influence of the particle size effect. 

These latter studies are labeled as “batch” 

studies 

The selected samples from the different sites 

were treated in the following manner (see 

Figure 3-1). 

First, for the samples that contained large 

pieces of slag it was necessary to fracture 

the material into smaller pieces in order to 

conduct column or batch studies. This 

fractured material is subsequently referred to 

as “coarse” (2mm < particle size < 7mm) 

material. In addition, samples of the 

fractured material were ground to a very fine 

size (< 2mm) for chemical analysis, 

radiological analysis, and for use in the 

solubility studies. The use of fine material 

in the solubility studies was necessary to 

speed the reaction rate and achieve, if 

possible, equilibrium between solid phase 

components of the samples and the 

solutions. Surface area analysis was 

conducted on both the coarse and fine 

material using a Micrometrics Model 2010 

BET analyzer. 

Following sample fracturization the 

materials were used in the following general 

manner. Samples of fine material were sent 

for chemical, radiological, particle size 

(selected samples only) analysis and were 

used in all solubility studies. In addition, 

selected fine material was used in “fine” 

batch studies to contrast the leaching 

characteristics of the fine and coarse

material. Coarse material was used only in 

the batch and column studies. The 

following discussion provides more details 

on the analysis procedures and sample 

preparation for the solubility, batch, and 

column studies.

5
Methods and Materials 

Receive Samples 

at PNNL

Screen 

Samples 

(GM reading)

Non radioactive or

low activity

No studies

Fracture Sample

Sample selected

Coarse 

Material

Fine 

Material

Batch and Column 

Studies

Solubility 

Studies

Chemical 

Analysis

Radiological 

Analysis

Figure 3-1. Schematic outline of sample treatment and analysis. 

6
Methods and Materials 

3.1 Chemical Analysis Procedures 

Total chemical analysis of solid materials 

was performed by energy dispersive x-ray 

fluorescence (EDXRF) with low (ppm) 

detection limits for most elements from Al 

to Ce. 

Chemical analysis of solutions was 

performed by inductively coupled plasma

spectroscopy (ICP) analysis, except for 

samples with low concentrations of Th, U, 

or Nb, which were determined by 

inductively coupled plasma mass 

spectrometry (ICP-MS). Selected samples 

for anion analysis were also conducted using 

a model 4000i Dionex ion chromatograph. 

All analyses were performed under 

guidelines provided in PNNL QA good 

laboratory practice procedures: ICPMS 

(PNNL-AGG-415); ICP (PNNL – AGGICP-AES); IC (EPA method 300, “The 

determination of inorganic anions in water 

by ion chromatography); and XRF (use of 

NBS standard reference materials). 

3.2 Radiological Analysis 

Radiological analysis of solid and solution 

samples were conducted using a highefficiency intrinsic Germanium detector 

calibrated over the energy range 60 to 2000 

kev. The following energy peaks was used 

to determine the radionuclide 

concentrations: Ac-228, 911 kev; Bi-212, 

727 kev; Pb-212, 239 kev; Ra-226, 186 kev; 

Bi-214, 609 kev; Pb-214, 352 kev; Th-234, 

62.3 kev; Tl-208 583 kev. All analyses were 

performed on duplicate or triplicate samples. 

The Ra-226 values were corrected by a 

factor of 0.57 to account for the coincident 

natural U-235 peak. Selected solid samples 

were also dissolved with KOH-KNO3 fusion 

and chemically separated the U and Th. 

Uranium was then measured by kinetic 

phosphorescence and Th isotopes by alpha 

spectroscopy. 

3.3 Solubility and Batch Studies 

Solubility studies were conducted in a 

controlled atmosphere chamber under an 

atmosphere of ultrapure argon. Solubility 

studies were conducted in initially deionized water which had been pH adjusted 

using HCL to cover a broad range of pH 

values extending from approximately 1 to 12 

depending upon the specific samples 

examined. Batch studies were conducted 

both in an atmospheric chamber in the 

absence of CO2 and on the bench top where 

CO2 was allowed into the samples. Deionized water was used in all batch studies. 

The bench top studies were conducted as 

both “long term” and “short term” 

experiments. In the “long term” studies the 

samples were kept lightly capped but there 

was no forced equilibration with 

atmospheric CO2. (pCO2 ~10-3.5 atm). In the 

“short term” studies the samples were 

vigorously bubbled with air over a three-day 

period to insure the equilibration with 

atmospheric CO2. The introduction of CO2

is potentially important owing to the 

possible formation of either Th(IV) 

carbonate complexes (Felmy et al. 1997) or 

U carbonate complexes (Grenthe et al. 

1992). All of the batch studies were 

conducted at the “natural” pH of the sample, 

which varied with reaction time, and 

conditions, as the samples dissolved. No pH 

adjustments were made by adding acid or 

base. Both fine and coarse material was used 

in the batch experiments. All of the fine 

batch and solubility suspensions were 

prepared in the following manner. For each 

site sample a solid/solution suspension was 

7
Methods and Materials 

prepared by placing approximately one gram

of fine material in 30ml of deionized water 

in each 50ml centrifuge tube. 

Approximately 24 such suspensions were 

prepared for each sample in the solubility 

studies. Each sample was independently 

adjusted to a different pH value within the 

prescribed range using reagent grade HCl or 

NaOH. The batch samples were prepared in 

the same manner but only two suspensions 

(duplicates) were prepared for each site 

sample. All suspensions were then placed on 

an orbital shaker and shaken until sampling. 

Sampling of the solubility and batch 

suspensions consisted of pH measurements 

followed by centrifugation at 2000 x g for 7 

to 10 min. A sample of the supernatant was 

then filtered through Amicon type F-25 

Centriflo membrane cones with effective 

2500-molecular-weight cutoffs and 

approximately 0.0018-μm pore sizes. The 

membrane were pretreated by washing with 

pH adjusted deionized water (to the 

approximate pH of the sample) followed by 

filtration of a 0.5 ml to 1.0 ml aliquot of 

sample to saturate any adsorption sites. The 

aliquot of the sample was then discarded. 

This pretreatment process was then followed 

by filtration of approximately 5ml of

sample. Approximately 1ml of this sample 

was then withdrawn and acidified for ICP or 

ICP-MS and radiological analysis. The 

remaining unacidified sample was retained 

for anion analysis by IC. 

The coarse batch studies were conducted in 

the identical manner to the fine batch studies 

except that approximately 6g of sample were 

added to 180ml of deionized water in 500ml

polypropylene bottles. This procedure 

maintained the same solid/solution ratio as 

in the fine batch but allowed more particles 

of the larger material to be included in each 

sample. 

3.4 Column Studies 

Flow through column experiments were 

conducted using 32ml Savelex® teflon 

columns, Figure 3-2, connected to 3M 

modular infusion pumps operating at a flow 

rate of 0.1 ml/hr. Each 32ml column was 

then packed with 30 to 40g of slag material 

depending upon the exact particle size. The 

final solution volume in each column (pore 

volume) was then approximately 16 to 

17mls. Porous frits were placed at the top 

and bottom of each column to prevent any 

fine suspended material from passing 

through the column. The solutions entered 

the columns through the bottom and passed 

out the top into a sealed collection bottle. 

Samples from the collection bottle were 

taken, pH measurements made, and filtered 

as described for solubility and batch studies. 

Filtrates were split into acidified and 

unacidified aliquots for analysis by ICP or 

ICP-MS and IC. Radiological analysis was 

also performed on acidified sample. 

8
Methods and Materials 

Figure 3-2. Schematic of Column Apparatus. The designation “soil” represents soil or slag 

depending upon the specific sample. The pH port, which was present on only a few 

columns, was not used. All pH measurements were made in the sample collecting 

vessel. 

9
Methods and Materials 

10
Results and Discussion 

4 RESULTS AND DISCUSSION 

4.1 Chemical Analysis 

The total chemical analysis of the soil and 

slag samples at all three sites, Tables 4-(1-

3), show a bulk composition dominated by 

Al, Si, and Ca characteristic of aluminosilicate minerals or calcium alumino-silicate 

minerals with significant amounts of Fe and 

significant amounts of Nb. These same

general chemical characteristics, with 

somewhat lower Fe content, have been 

reported elsewhere (Pickett et al. 1998) and 

have been correlated with the presence of 

several alumino-silicate minerals including 

gehlenite, wollastonite, and pervoskite 

(Table 4-4). The presence of high 

concentrations of Nb, and to a lesser extent 

Ta, at least Site C, being a clear indication 

of materials originating from the ferrocolumbium smelting process. Also, of 

interest is the presence of significant 

amounts of Zr which is correlated with the 

presence of zirconate minerals (calzirtite and 

zirconolite; Table 4-4) and a relatively high 

Mo content in slags from Site A. 

The element in highest concentration with 

radioactive isotopes is Th. Th occurs in 

significant concentration in all samples, as 

high as 1.4% in Site A samples. The 

concentration of U is fairly uniform in all 

samples averaging approximately 200ppm.

The mineral phases in which these 

radionuclides are incorporated in does vary 

somewhat between the sites. The major Th 

bearing phase is perovskite at sites A and C 

(Veblen et al. 2000). However, significant 

amounts of thorianite (ThO2) also present at 

site A (Table 4-4). At site B the Th and U 

are primarily contained in perovskite, 

calzirtite, and pyrochlore. 

Chemical analysis of well and surface 

waters were also conducted at Site C. The 

analyses are reported for filtered samples in 

Table 4-5 and unfiltered samples in Table 4-

6. Filtration was necessary since the 

samples as received at PNNL contained 

brownish to rust colored solids. The well 

waters are all predominately Na, Ca, Mg, 

SO4, HCO3 solutions at near neutral pH 

values. Well #8 contains the highest 

concentrations of these components and 

hence has the highest ionic strength. 

Dissolved Th and U concentrations were 

quite low in all samples with Th 

concentrations at or below the analytical 

detection limit. Dissolved U concentrations 

were detectable but quite low (~ 1ug/l). No 

other radionuclides were present at 

concentrations >1pCi/l in any water sample 

taken at the site. 

The analyses of the unfiltered samples 

showed the same trends as the filtered 

samples with the exception of significant 

concentrations of Fe, Si, and sometimes Al 

in the analyses. These components are 

indicative of the inclusion of solids in the 

analyses. The particulate material associate 

with well #10 is clearly aluminosilicate 

dominated from the high fractions of Al and 

Si as well as the enriched K concentration. 

The other samples are somewhat more 

difficult to distinguish owing to the 

relatively high detection limits for Al and Si. 

However, there does appear to be some

enrichment in Fe, most likely as the result of 

precipitation of iron oxide/hydroxides in the 

sample upon exposure to air. Such a 

conclusion is partially supported by the onsite dissolved oxygen (DO) readings (Table 

4-5), which show depressed values 

especially for well sample #9. Eh 

measurements of these samples taken at 

11
Results and Discussion 

PNNL all showed relatively high and 

oxidizing readings (~500mv vs SHE), 

indicating that the samples were initially 

oxidized or became oxidized during 

shipping and storage. 

The well water analyses shown in Table 4-5 

for Site C were also used as input for 

geochemical modeling calculations using the 

MINTEQA2 equilibrium model (Allison et 

al. 1991). These results showed that the 

soluble chemical species for U were 

dominated by aqueous carbonate complexes, 

principally by the dicarbonate species 

UO2(CO3)2

2- at the pH of the samples (6-7), 

Figure 4-1 Such anionic species can be 

highly mobile in groundwater systems, 

although the total species concentration was 

quite low as the data in Table 4-5 indicate. 

The chemical modeling calculations also 

indicated that the well waters are near 

saturation with the mineral calcite (CaCO3). 

If the laboratory pH values are used in these 

calculations calcite appears to be slightly 

supersaturated. However, if the lower field 

pH values are used in the calculations calcite 

appears to be in equilibrium or slightly 

undersaturated. No other mineral 

equilibrium was indicated in the modeling 

calculations. 

12
Results and Discussion 

Table 4-1. Chemical composition of slags at Site A. 

Element (ppm) Site A Slag 1 Site A Slag 2 Site A Slag 3 Site A Slag 4

Al 200000±17000 192000±17000 234000±19000 229000±1800

Si 88800±7400 928000±7900 86100±7500 90400±7600 

K 1110±160 1450±180 1050±170 1130±160 

Ca 75700±5300 85100±6000 85100±6000 82200±5800 

Mn 840±160 950±180 690±170 660±160 

Fe 27300±1900 31200±2200 26000±1900 26700±1900 

Ni <57±57 <64±64 <64±64 <57±57

Cu 218±34 250±39 223±36 436±47

Zn 66±20 84±23 <38±38 103±20

Ga <32±32 <34±34 <35±35 <32±32

Hg <23±23 <24±24 <21±21 <22±22

Se <35±35 <33±33 <35±35 <332±33

Br <18±18 <17±17 <17±17 <17±17

Rb <19±19 <18±18 <18±18 <18±18

U 248±22 218±20 230±21 262±23

Sr 169±28 330±25 382±28 372±28

Y 68±11 67.3±10 64±10 76±11

Nb 27500±1900 23600±1700 26900±1900 26800±1900 

Mo 2980±210 3530±250 2260±160 2460±170 

Th 13290±940 12060±850 14190±1000 13760±970

13
Results and Discussion 

Table 4-2. Chemical composition of samples collected at Site B. 

Element 

(ppm) 

Slag A 

(96T-C-9) 

Ore 

(96T-C-19) 

Soil B5 

(96T-C-20) 

Ore 

(96-T-C-21) 

Al 45000±3900 315000±23000 543000±5000 95200±7400 

Si 337000±24000 119400±8700 281000±20000 164000±1200 

P <1500±1500 <2900±2900 <2600±2600 

Cl <110±110 <250±250 <190±190 <260±260 

K 6500±460 3640±270 6200±450 1510±140 

Ca 26500±1900 137500±9600 98900±6900 217000±15000 

Ti 8270±580 19800±1400 25700±1800 66000±4600 

Mn 2420±180 2270±190 5600±410 5070±380 

Fe 59400±4200 26500±1900 91700±6400 13730±970 

Ni 71±15 82±24 77±32 <53±53 

Ta 1230±100 5070±360 7750±560 12130±860 

Pb 461±34 28100±2000 1600±110 <28±28 

As 280±22 1062±92 616±48 

U 75.8±6 243±18 213±16 371±27

Th 364±27 2240±160 1108±79 2380±170 

Sr 125±9 144±11 165±12 162±12

Y 274±19 1312±92 849±60 2460±190 

Zr 4070±290 15600±1100 11740±820 23600±1600 

Nb 3860±270 7120±500 13290±930 8320±580 

Mo <7.0±7 <16±16 <28.7±7.3 <18±18 

W 803±67 191±63 2330±190 1970±150 

S 1290±200 2060±610 1110±33 

Cd 26±10 66.9±9 <17±8.2 <8.7±8.7 

Sn 1059±76 1490±110 1970±140 205±12 

Sb <23±23 931±66 183±16 <11±11 

Ba 402±41 197±28 243±31 <48±48 

La 598±61 2690±200 1600±120 3220±170 

Ce 1540±130 6340±450 3970±290 7370±380 

14
Results and Discussion 

Table 4-3. Chemical composition of slag samples 1 and 2 at Site C. 

Element 

(ppm) 

Site C 

Slag 1 

Site C 

Slag 2 

Al 376000±27000 420000±30000 

Si 102600±8300 34700±4400 

K 4700±340 5110±370 

Ca 59200±4200 41700±2900 

Mn 5110±420 420±130 

Fe 23600±1700 17300±1200 

Ni 11320±800 230±30

As 250±20 1130±80 

U 260±20 280±20

Sr 1000±70 1550±110 

Y 660±50 450±30

Nb 42900±3000 63400±4400 

Mo 160±10 260±20

Zr 3490±240 3940±280 

Th 2130±150 10170±710

15
Results and Discussion 

Table 4-4. Minerals present at sites A, B, and C (Veblen et al. 2000). 

Phase Ideal formula Site where present 

Calzirtite* (Ca,U,Th)ZrTi2O7 all 

Zirconolite* (Ca,Th,Ce)Zr(Ti,Nb)2O7 all 

Perovskite* CaTiO3 all 

Perovskite (Loparite) (Ca,Ce,Th)(Ti,Nb)O3 Site A and B 

Zirconolite (Ca2.45Th0.03REE0.04)Zr0.34Al0.30Ti1.24 

Nb0.15Ta0.12O7 

Site B 

Zirconolite (Ca 1.18 Ce0.61Th0.11REE0.26) 

Zr0.02Al1.17Ti1.14Nb0.08O7

Site B 

Pyrochlore (Betafite) (Ca,U,Ce)2(Nb,Ti)2O6 Site A and B 

Pyrochlore (Ca,Th,Ce)2(Nb,Ti)2O6 all 

Glass Si,Al,Ca,Ti,U,Th all 

Hibonite (Ca,Ce)9(Ti,Al)12O19 Sites A and C 

Barium Aluminate* Ba,Ce(Ti,Al)12O19 Site A and Site B 

Spinel* AB2O4 A = Co, Fe, Mg, Mn, Ni 

 B = Al, Cr, Fe, Mg, Mn, V 

all 

Periclase MgO Site B 

Wustite FeO Site B 

Monticellite CaMgSiO4 Site B 

Gehlenite Ca2Al(AlSi)O7 all 

Melilite (Ca,Na)2(Mg,Fe,Al,Si)307 Site C 

Clinopyroxene Ca(Zr,Ti,Al)(Al,Si,Ti)2O6 Site C 

Feldspar CaAl2Si2O8 all 

Wollastonite CaSiO3 Site C 

Ce-Silicate Ce,Si Site C 

Ce-Aluminosilicate Ce,Si,Al Site C 

Barium Aluminosilicate BaAl2Si2O8 Site A 

Gypsum Ca(SO)4 Site A 

Tridymite SiO2 all 

Groundmass Ca,Ba,Al; Ca,Ba,S,Cl,Al Site A 

* indicates SYNROC phases

16
Results and Discussion 

Table 4-5. Chemical analysis of filtered water and well samples at Site C. Field data supplied 

by SCIENTECH Inc. DO represents dissolved oxygen. Concentrations in mg/l, pH 

in units. Inorganic carbon (IC) in mg/l as C. Alkalinity is reported as mg/l as CaCO3

with the value in parentheses converted to mg/l as C for comparison with the IC 

analysis. 

MW #1 MW #5 MW #6 MW #8 MW #9 MW #10 River 

pH (lab) 7.48 7.52 7.52 7.55 7.86 7.48 7.32

pH (field) - - - 6.38 6.97 6.80 - 

DO (field) - - - 4.2 0.60 6.8 - 

Na 16 45 32 101 34 45 10

K 2.0 11 5.6 27 2.1 8 2.0

Ca 135 48 99 293 201 120 24

Mg 23 22 22 49 49 60 5

Cl 18 14 20 24 80 25 18

F 0.2 1.2 0.9 0.7 0.1 0.6 0.1

IC* 75 30 57 66 65 59 16

Alkalinity 205 (49) 132

(32) 

248 

(59) 

240 

(58) 

- 182

(44) 

65

(16) 

SO4 131 156 120 815 400 287 0.2

Th (ug/l) < 0.25 <0.25 < 0.25 < 0.25 < 0.25 < 0.25 <0.25 

U (ug/l) 1.0 0.35 1.6 0.63 0.76 1.2 <0.25 

17
Results and Discussion 

Table 4-6. Chemical analysis of unfiltered water and well samples at Site C. Concentrations in 

mg/l, pH in units. Values in parentheses are the corresponding values for filtered 

samples to assist in distinguishing the chemical composition of the solids in the 

samples. 

MW #1 MW #5 MW #6 MW #8 MW #9 MW #10 

pH 7.42

(7.48) 

7.50

(7.52) 

7.49

(7.52) 

7.55

(7.55) 

- 

(7.86) 

7.46

(7.48) 

Al <135 <126 <165 <147 <132 221

K 2.6

(2.0) 

12 

(11) 

16 

(5.6) 

25 

(27) 

5.0 

(2.1) 

47 

(8) 

Ca 94 

(135)

40 

(48) 

89 

(99) 

208 

(293)

157 

(201)

107 

(120)

Mn 3.4 <0.048 0.9 0.28 0.38 2.1

Cl 24 

(18) 

19 

(14) 

27 

(20) 

36 

(24) 

87 

(80) 

30 

(25) 

Si <49 <49 188 <59 <53 860

Fe 16.6 1.9 34 1.5 2.2 102

SO4 134 

(131)

156 

(156)

127 

(120)

657 

(815)

344 

(400)

268 

(287)

Th (ug/l) < 0.1 < 0.09 < 0.1 < 0.1 < 0.08 < 0.1 

U (ug/l) < 0.1 < 0.08 < 0.1 < 0.1 < 0.07 < 0.1 

0

10

20

30

40

50

60

70

80

90

100

4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5

Percent

pH

UO2(CO3)

3

4-

UO2(OH)3

-

UO2(CO3)

2

2-

UO2CO3(aq)

UO2F+

 UO2

2+

UO2SO4(aq)

UO2F2(aq)

Figure 4-1. Calculated uranium species distribution for well #10 as a function of pH at site C. 

Anionic uranium complexes are the dominant species at the pH of the well sample, 6.8.

18
Results and Discussion 

4.2 Radiological Analysis 

Radiological analyses of site materials 

yields the isotopic composition of the 

radioactive elements. Such analyses are 

important not only for more detailed 

analyses of possible health effects but also 

the relative ratios of the various isotopes 

yields important information on isotopic 

separation processes that may have occurred 

at the site. This information is key to 

understanding the site history and waste 

disposal practices at the site. 

The ferrocolumbian slag at Site A contains 

about 1.3% Th-232 (Table 4-1 and 4-7) and 

is in secular equilibrium with all of its 

daughter products (see Table 4-7). The U238 appears to be in secular equilibrium

with Ra-226 but not with the Ra-226 

daughters, presumably as a result of the 

continuous escape of Rn-222 gas since 

disposal. These facts indicate the slags have 

a certain porous structure that allows escape 

of the Rn-222. This fact contrasts sharply 

with the results for Site B slags, described 

below, which do not show such a porous 

structure. 

In the case of Site B samples (Table 4-8), all 

four samples have Th-232 and U-238 in 

secular equilibrium with all their daughter 

products. Apparently the processing 

conditions at Site B did not result in the 

separation of the U-238 daughters. In 

addition, unlike at Site A, the Ra-226 

daughters are in secular equilibrium,

indicating only negligible escape of Rn-222 

has occurred since disposal. This is 

apparently related to the refractory nature 

and low permeability of Site B slag samples. 

In the case of Site C samples (Table 4-9) 

both samples show the slag samples to be in 

secular equilibrium with the U-238 

daughters. It is likely that Th-232 is also in 

secular equilibrium with its daughters, 

although this is clearly apparent only for 

slag 2. The radiological analysis of slag 1 

shows only about 65% of the Th-232 can be 

seen in the daughters. This is most likely a 

slight subsampling error since the same

effect is seen in subsample 1 of slag 2 but 

not subsample 2 of slag 2. 

The U and Th isotopic analyses (Table 4-10) 

support the above results based upon gamma 

spectroscopy. Th-232 and daughters are in 

secular equilibrium. In the case of U-238, 

the Th-230 daughter appears to be somewhat 

lower in activity than the parent U-238 but 

this lower activity is in proportion to the 

lower activities observed for the other Th 

isotopes, Th-232 and Th-228, relative to the 

gamma spectroscopy analyses. Apparently 

not all of the Th was dissolved in the KOHKNO3 fusion process before alpha 

spectroscopy and the presence of 

undissolved solids was noted for these 

samples. The undissolved solids apparently 

contained small quantities of insoluble Th. 

Examples of alpha spectroscopy analysis for 

sites A and B are shown in Figures 4-2 and 

4-3, respectively.

19
Results and Discussion 

Table 4-7. Radiological analysis of slags at Site A. All analyses represent the average of three 

subsamples of each slag. Values in pCi/g. 

Nuclide Site A 

Slag 1 

Site A 

Slag 2 

Site A 

Slag 3 

Site A 

Slag 4 

Th Series 

 Th-232 (1460) (1330) (1560) (1510)

 Ac-228 1,270 1,100 1,360 1,250 

 Th-228 1,190 980 1,200 1,200 

 Ra-224 1,440 1,300 1,500 1,390 

 Pb-212 1,390 1,200 1,490 1,370 

 Bi-212 1,530 1,310 1,610 1,510 

U-238 Series 

 U-238 (80) (70) (75) (85) 

 Ra-226 90 75 90 80 

 Pb-214 45 45 40 45 

 Bi-214 40 45 35 40 

U-235 Series ** 

** Uranium values are close to detection limit and because of interferences are hard to quantify with the counting

system. Values in parenthesis are calculated from the XRF data for thorium and uranium assuming all of the Th is 

Th-232 (1.1x10-7Ci/g) and all of the U is U-238 (3.3x10-7Ci/g). 

20
Results and Discussion 

Table 4-8. Radiological analysis of Site B samples. Slag A(96T-C-9),Grayish Green Ore(96TC-19), Soil Site B5(96T-C-20), and Ore (96T-C-21). Results in pCi/g. 

Nuclide Site B 

Slag A 

Site B 

Ore 

Site B 

Soil B5

Site B 

96T-C-21 Ore

Th Series 

 Th-232 (40) (246) (120) (262)

 Ac-228 43 176 97 246 

 Pb-212 42 160 100 238 

 Bi-212 49 197 112 266 

U-238 Series 

 U-238 (25) (80) (70) (123)

 Th-234 140 

 Ra-226 33 121 78 180 

 Pb-214 29 111 70 210 

 Bi-214 27 101 63 192 

U-235 Series ** 

** Uranium values are close to detection limit and because of interferences are hard to quantify with the 

counting system. Values in parenthesis are calculated from the XRF data for thorium and uranium

assuming all of the Th is Th-232 (1.1x10-7Ci/g) and all of the U is U-238 (3.3x10-7Ci/g). 

21
Results and Discussion 

Table 4-9. Radiological analysis of Site C samples. Results in pCi/g. 

Nuclide Site C 

Slag 1 

Site C 

Slag 2 

Th Series 

 Th-232 (230) (1120)

 Th-228 159 941 

 Ac-228 136 921 

 Pb-212 151 944 

 Bi-212 161 1060

 Tl-208 142 951 

U-238 Series 

 U-238 84 142 

 Pb-214 75 105 

 Bi-214 74 112 

U-235 Series

 U-235 5 6 

Values in parenthesis are calculated from the XRF data for thorium assuming all of the 

Th is Th-232 (1.1x10-7Ci/g). 

Table 4-10. Uranium and thorium isotopic analyses of selected samples. Results in pCi/g. 

Nuclide Site A 

Slag 1 

Site B 

Sample C-19 

Th Series 

 Th-232 946 64 

 Th-228 955 63 

U-238 Series 

 U-238 81 72 

 U-234 81 72 

 Th-230 59 38 

 U-235 3.8 3.4 

22
Results and Discussion 

60

40

20

0

3500 4000 4500 5000 5500 6000 6500 7000

Energy (keV)

Th-232

Th-230

Th-228

Ra-224

Bi-212

Rn-220

Po-216

60

40

20

0

3500 4000 4500 5000 5500 6000 6500 7000

Energy (keV)

Th-232

Th-230

Th-228

Ra-224

Bi-212

Rn-220

Po-216

Counts

Figure 4-2. Example Alpha Spectra of Site A samples. 

80

60

40

20

0

4000 5000 6000 7000 8000

Energy (keV)

Th-232

Th-230

Th-228

Ra-224

Bi-212

Rn-220

Po-216

Counts

Figure 4-3. Example Alpha Spectra of Site B samples. 

23
Results and Discussion 

4.3 Solubility and Leaching Studies 

4.3.1 Site A 

4.3.1.1 THORIUM

The solubility data for Th at Site A show 

very low solubilities except at low pH 

values (<5) where the solubilities increase 

rapidly (Figure 4-4). A comparison of these 

solubility data with the calculated 

solubilities for possible Th solid phases, 

solid and dashed lines in Figure 4-4, show 

that the aqueous Th concentrations are most 

likely controlled by thorianite (ThO2(c)) or 

possibly, at very low pH a Th-silicate 

(i.e.ThSiO4(gl)). Mineralogical analysis of 

these samples (Table 4-5), show the 

presence of some thorianite. The presence 

of this phase leads credence to the 

possibility that this phase is the primary 

solubility control. If a ThSiO4(gl) phase 

does form it is most likely a secondary phase 

precipitated as a result of the dissolution of 

large concentrations (> 200mg/l) of Si at 

low pH. The difference in observed 

solubility between the thorianite solubility at 

the somewhat higher observed solubilities 

between pH 4 and 5 also indicates the 

presence of a small amount of amorphous 

ThO2(am). In any event, the Th 

concentrations in Site A samples appear to 

be solubility limited, either by ThSiO4(gl) at 

very low pH, ThO2(c), or by trace amounts 

of ThO2(am), and show very low solubilities 

over a broad range of pH values. 

The batch leaching data for Site A samples 

show that the slag materials tend to buffer 

the solution pH values in the alkaline region 

(> 10, see Table 4-11). Although we cannot 

be sure, these high pH values are most likely 

related to the dissolution of alkaline earth 

compounds containing either Ca or Ba that 

are present in these samples. As seen from

the solubility data, these high pH values are 

expected to maintain the dissolved Th

concentrations at very low levels. The 

observed Th concentrations in the batch 

leaching studies, Figure 4-5, follow this 

expected trend. Th concentrations are 

uniformly low in both the coarse and fine 

material with maximum concentrations 

about 10-7.5M (3.2x10-8M). As expected, if a 

solubility controlling solid was present, 

there should be no clear differences between 

coarse and fine material (i.e. no surface area 

or particle size effect). The pH values for 

the “long term” samples exposed to CO2, 

Table 4-12, show very similar values to 

those in the absence of CO2 indicating that 

the light capping of these samples prevented 

influx of sufficient CO2 to equilibrate the 

solutions, with the possible exception of the 

longest term (45 day) samples. However, 

the “short term” studies with vigorous 

bubbling show much lower pH values more 

typical of equilibration with atmospheric 

CO2. However, even with this introduced 

CO2 the dissolved Th concentrations 

remained at or near the detection limit of 10-

8.5

M. This fact appears to result from the 

relatively low final inorganic carbon content 

(<0.002M) which was constrained either by 

the dilute nature of the solutions or the 

apparent precipitation of carbonate minerals 

owing to the high concentrations of alkaline 

earth cations in some samples. 

The pH values in the column experiments, 

Table 4-13, show a trend of much lower 

values than in the batch experiments. This 

results from the leakage of small amounts of 

atmospheric CO2 into the sampling bottle 

during the duration of the column study. 

However these pH values also fall in the low 

solubility region, see Figure 4-4. The 

observed Th concentrations in the column

24
Results and Discussion 

experiments, Figure 4-6, follow this 

expected trend with all of the Th 

concentrations all at or below the analytical 

detection limit of approximately 10-8.5M.

-9

-8

-7

-6

-5

-4

012 3 4567 8 9 10 11 12 13

log Th(M)

pH

 4 Days

31 Days

275 Days

ThO2(am)

ThO2(c) ThSiO4(gl)

Figure 4-4. Th concentrations in Site A Solubility Studies. 

igure 4-5. Th concentrations in Site A Batch Leaching Studies. 

-9

-8

-7

-6

-5

-4

0 5 10 15 20 25 30 35 40 45

log Th(M)

Days

Fine material

Coarse Material (Sample A)

Coarse Material (Sample B)

Detection Limit and Concentration in "Solubility" Studies.

F

25
Results and Discussion 

-9

-8

-7

-6

-5

-4

0 10 20 30 40 50 60 70 80 90 100

log Th or U(M)

Pore Volumes

Th U

Detection Limit

Approximate Uranium Concentration in Coarse Batch Study

Figure 4-6. Th and U concentrations in Site A Column Studies. 

Table 4-11. Measured pH values in batch leaching studies as a function of time. 

Leaching Time Site A 

Fine Material

Site A 

Coarse Material

2 hrs. 9.39 7.62 

6 hrs. CO2 9.75 

3 days 10.15 10.33 

7 days 10.45 10.33 

15 days 10.31 9.84 

37 days 10.23 

45 days 10.66 

26
Results and Discussion 

Table 4-12. pH values measured in batch studies exposed to atmospheric CO2. 

“Long Term” “Short Term” 

2 hrs. 3 days 7 days 14 days 45 days 0.75 days 3 days 

Site A 9.29 10.26 10.4 10.37 10.55 8.07 7.97

Site B(C-9) 8.41 9.44 9.48 9.38 9.34 7.76 8.03

Site B(C-19) 7.62 8.71 8.84 8.61 9.25 7.73 7.89

Site B(C-20) 7.39 8.56 8.36 8.10 7.74 7.73 7.83

Table 4-13. Measured pH values in column studies as a function of time. 

Leaching Time Site A Site B

4 days 7.96 

5 days 8.23 

8 days 8.21 

11 days 7.64 

30 days 8.22 8.43 

72 days 8.38 

78 days 8.29 

In summary, the aqueous Th concentrations 

in Site A samples are solubility controlled, 

either by ThO2(c), ThO2(am), or at very low 

pH, ThSiO4. The presence of a solubility 

limiting phase results in the leachable Th 

concentrations being independent of total 

sample particle size or surface area. The 

apparent rapid dissolution of the solubility 

limiting phase(s) results in consistent results 

between the solubility, batch, and column

studies. The solubility controlling solid 

phases for Th are all very insoluble at pH 

values > 5. 

4.3.1.2 URANIUM

Uranium, even if present as insoluble U(IV) 

solid phases, is easily oxidized in solution to 

U(VI). The majority of U(VI) containing 

solid phases (Krupka and Serne 1998) are 

highly soluble (>10-4M). One of the major 

exceptions to this rule of insoluble U(VI) 

phases is in solutions of high pH, low 

carbonate, and high concentrations of 

alkaline earth cations. These solutions result 

in the precipitation of insoluble alkaline 

earth uranates {i.e. strontium uranate 

(SrUO4(c)), or becquerelite 

(CaU6O19.

11H2O)}. These are precisely the 

conditions found for Site A samples, Table 

4-11 and Figure 4-7. As a result, such 

phases, particularly the calcium uranates 

could limit U (VI) solubilities at Site A. 

Unfortunately, experimental data on the 

solubility of these phases is very limited. As 

a result, in another task of this project, the 

solubility of becquerelite was measured over 

a broad range of pH values and dissolved Ca 

27
Results and Discussion 

concentrations (see Appendix C). A 

summary of the results is presented in 

Figure 4-8. Interestingly, these data show 

that solid phases such as bequerelite can 

maintain quite low (10-7M) dissolved U (VI) 

concentrations at the high pH and dissolved 

Ca concentrations that could occur at Site A. 

The actual solubility data for U in samples 

from Site A, Figure 4-9, show quite low 

solubilities across the entire pH range. 

Although these concentrations are obviously 

not limited by becquerelite at low pH values, 

the solubilities at higher pH (>8) could be 

limited by the solubility of such phases. 

The batch leaching data for U in the absence 

of CO2 also show low dissolved 

concentrations (Figure 4-10) with some

difference between fine and coarse material. 

The “solubility” data at the same pH 

appearing to be intermediate between the 

fine and coarse batch results. The 

differences do not appear to be due to 

differences in Ca concentrations, which are 

very consistent between the coarse batch, 

fine batch, and solubility studies (i.e. 100 - 

120mg/l as Ca). The results for the batch 

studies in the presence of CO2 all show U 

concentrations at or near the detection limit 

(~10-8.5 M), indicating no significant 

solubilization effect on U of introduced 

CO2. The results for the column studies, 

Figure 4-6, also show quite low solubilities 

and are in excellent agreement with the 

coarse batch studies. 

In summary, although the solubility 

controlling mechanism for U in Site A 

samples is not precisely known, the fact that 

the U concentrations are relatively low is not 

entirely unexpected for these high pH, low 

carbonate, high alkaline earth solutions. The 

solubilities can be limited by becquerelite at 

high pH values. The dissolved 

concentrations of U are consistent between 

the coarse batch and the column studies, 

which allows useful calculations to be made 

on solubility and leaching rates (see below).

-6

-5

-4

-3

-2

-1

012 3 4 56789 10 11 12 13

log C(M)

pH

Ca 

Sr

Ba

Figure 4-7. Alkaline Earth Cation Solubilities in Site A Samples. 

28
Results and Discussion 

Figure 4-8. Aqueous uranium concentrations contacting becquerelite suspensions in 0.1M CaCl2

and over a range of hydrogen ion concentrations (pCH+ values). The designation 

(mol/dm–3) is equivalent to moles/l. See Appendix C for a detailed explanation. 

-9

-8

-7

-6

-5

-4

0 123456 7 8 9 10 11 12 13

log U(M)

pH

 4 Days

31 Days

Becquerelite

(calculated)

Becquerelite

(experimental)

CaUO4(c)

Figure 4-9. U concentrations in Site A Solubility Studies. The calculated becquerilite values use 

thermodynamic data taken from Grenthe et al. (1992), see Appendix C. 

29
Results and Discussion 

-9

-8

-7

-6

-5

-4

0 5 10 15 20 25 30 35 40 45

log U(M)

Days

Fine material

Coarse Material (Sample A)

Coarse Material (Sample B)

Concentrations Observed in "Solubility" Studies

Figure 4-10. U concentrations in Site A Batch Leaching Studies. The area designated for the 

solubility study values represents the range of observed concentrations. 

4.3.1.3 OTHER RADIONUCLIDES 

Only very low concentrations of other 

radionuclides were detected in the solubility 

studies, batch studies or column studies. All 

Th-232 or U-238 daughters were either 

completely undetectable or found to be very 

low, typically <2pCi/ml. The only 

exceptions were the 14 pCi/ml of Bi-212 

and 11pCi/ml of Pb-212 were found in the 

most acid solubility point analyzed (pH = 

3.5) and Ra-226, which showed soluble 

concentrations in the solubility studies as 

high as 16pCi/ml. There was also evidence 

for some Pb-210, but the uncertainties of 

these analyses were so high as to prevent 

quantitiation, and Cs-137 from fallout at 

concentrations <2pCi/ml. 

4.3.2 Site B 

4.3.2.1 THORIUM 

The solubility data for Th in three samples 

from Site B, Figure 4-11, show a very 

consistent trend of very low solubilities, 

except at the very lowest pH values. Sample 

C-19, the greyish green slag showed the 

highest solubilities consistent with the total 

analyzed Th concentrations in these 

samples. Interestingly, the observed Th 

solubilities for Site C samples are in general 

even lower than for Site A slag, with only 

the solubility in the C-19 sample apparently 

limited by thorianite, ThO2(c). 

30
Results and Discussion 

-10

-9

-8

-7

-6

-5

-4

-3

0 1 2 3 4 5 6 7 8 9 10 11 12 13

log Th(M)

pH

C9 - 5 Days

C9 - 113 Days

ThO2(c)

(a)

-10

-9

-8

-7

-6

-5

-4

-3

0 1 234 5 6 7 8 9 10 11 12 13

log Th(M)

pH

 C19 - 5 Days

C19 - 113 Days

ThO2(am)

(b)

ThO2(c)

-10

-9

-8

-7

-6

-5

-4

-3

0 1 2 3 4 5 6 7 8 9 10 11 12 13

log Th(M)

pH

 5 Days

106 Days ThO2(c)

(c)

Figure 4-11. Th concentrations in Site B Solubility Studies. 

31
Results and Discussion 

In the case of the batch leaching 

experiments, the solution pH values were 

generally basic but highly variable, Table 4-

14. This variability is apparently related to 

the changing nature of the solutions as a 

result of a very slow dissolution rate. The 

slow dissolution rate is apparent from the 

dissolved Ca concentrations, the dominant 

cation, which increase only very slowly with 

time. The fact that the solutions are so

poorly buffered may also impact the pH 

meter readings. In any event, the pH values 

are in general between 8 and 10. The 

corresponding Th concentrations in the 

batch leaching samples in the absence of 

CO2, Figure 4-12, show quite low 

solubilities and bracket the range of Th 

concentrations expected from the solubility 

studies. The Th concentrations in the batch 

leaching studies exposed to CO2 were also 

very low and close to the analytical 

detection limit of 10-8.5M. 

The column studies, Figure 4-13, also show 

very low dissolved concentrations with the 

majority of the samples at the analytical 

detection limit of 10-8.5M. As was true in 

the previous column studies of Site A 

samples, the measured pH values varied 

only over a very narrow range (i.e. 7.9 to 

8.8).

Table 4-14. Measured pH values and Ca concentrations in batch leaching studies as a function 

of time for Site B samples. 

Leaching Time C-9 C-19 C-20

pH Ca(mg/l) pH Ca(mg/l) pH Ca(mg/l) 

2 hrs. 7.86 1.5 7.83 1.5 7.57 2.9 

3 days 9.97 4.7 10.5 5.1 9.90 6.3 

7 days 9.12 6.9 9.30 8.7 8.93 8.6 

14 days 8.37 14.4 8.70 11.8 8.03 9.9 

45 days 9.12 14.6 9.70 24.3 8.54 13.1 

4.3.2.2 URANIUM 

Uranium solubilities in Site B samples, 

Figure 4-14, show very low solubilities in a 

similar fashion to the slag samples at Site A. 

At very high pH values, the solubilities 

could become limited by becquerelite, 

although the Ca concentration in these 

samples is about an order of magnitude 

lower than in Site A samples (see Figure 4-

15). The observed U concentrations in the 

batch leaching studies in both the presence 

and absence of CO2, Figure 4-16, also show 

very low dissolved U concentrations, which 

are in good agreement with the U solubility 

studies. Similarly, the U concentrations in 

the column studies, Figure 4-13, correspond 

to the batch leaching studies. No particle 

size or surface area effect is seen. In 

summary, the concentration controlling 

mechanism for U in Site B samples is not 

precisely known. Becquerelite could limit 

the solubility at high pH values, but this is 

less likely than in Site A samples owing to 

the lower dissolved Ca concentrations. It is 

32
Results and Discussion 

possible that the U concentrations are simply 

controlled by slow dissolution of the solid 

phase material, but this also appears unlikely 

since the dissolved concentrations in the 

solubility studies, which used ground, very 

small particle size material yielded similar 

results to the batch and column studies with 

different particle sizes and higher 

solid/solution ratios (column studies). It 

appears more likely that the U is tightly 

bound in either a very insoluble or refractory 

phase.

-9

-8

-7

-6

-5

-4

0 5 10 15 20 25 30 35 40 45

log Th(M)

Days

C-9 Sample 1

C-9 Sample 2

C-19 Sample 1

C-19 Sample 2

C-20 Sample 1

C-20 Sample 2

Detection Limit

 Concentration

Range for

Solubility

Studies

Figure 4-12. Th concentrations in Site B Batch Leaching Studies. 

-9

-8

-7

-6

-5

-4

0 10 20 30 40 50 60 70 80

log C(M)

Pore Volumes

Th U

Detection Limit

Figure 4-13. Th and U concentrations in Site B Column Studies. 

33
Results and Discussion 

-10

-9

-8

-7

-6

-5

-4

-3

0 1 234 5 6 789 10 11 12 3

log U(M)

pH

C9 - 5 Days

C9 - 113 Days

 C19 - 5 Days

C19 - 113 Days

C20 - 5 Days

C20 - 106 Days

Becquerelite

1

igure 4-14. U concentrations in Site B Solubility Studies. 

igure 4-15. Calcium concentrations in Site A and Site B Solubility Studies. 

F

-6

-5

-4

-3

-2

0123 4567 8 9 10 11 12 13

log Ca(M)

pH

Site A

Site B (C-9)

-1

F

34
Results and Discussion 

-9

-8

-7

-6

-5

-4

0 5 10 15 20 25 30 35 40 45

log U(M)

Days

C-9 Sample 1

C-9 Sample 2

C-19 Sample 1

C-19 Sample 2

C-20 Sample 1

C-20 Sample 2

Detection Limit

Concentration

Range in

Solubility

Studies

Figure 4-16. U concentrations in Site B Batch Leaching Studies.

4.3.2.3 OTHER RADIONUCLIDES 

The very refractory nature of Site B samples 

was also reflected in the leaching of U-238 

or Th-232 daughters. As was true with Site 

A samples, no Th-232 or U-238 daughters 

were detected at significant concentration in 

the solubility, leaching, or column studies. 

Bi-212 and Pb-212 were detected in a few 

samples, but the concentrations were so low 

and the uncertainty of the analysis so high 

that any quantification of concentration was 

impossible. 

4.3.3 Site C

In the case of Site C only a limited number 

of solubility and column studies were 

performed to check of the results for these 

slag materials were consistent with the 

results from Sites A and B. 

4.3.3.1 THORIUM 

The solubility data for Th in two samples 

from Site C, Figure 4-17, show the same

consistent trend of very low solubilities, 

except at the very lowest pH values, 

observed for samples from sites A and B. 

Once again this is an indication of a 

solubility controlling phenomena for Th in 

the slag samples. Upper limits on dissolved 

concentrations most likely being set by 

amorphous or crystalline thorium oxide 

solubility.

35
Results and Discussion 

-10

-9

-8

-7

-6

-5

-4

-3

0 1 2 3 4 5 6 7 8 9 10 11 12 13

log Th(

M)

pH

Sample 1 - 4 days

Sample 1 - 13 days

Sample 2 - 4 days

Sample 2 - 13 days

ThO2(am)

ThO2(c)

Figure 4-17. Thorium concentrations in Site C Solubility Studies. 

These low solubilities are also reflected in 

the low dissolved concentrations seen for 

Site C column studies (Figure 4-18) which 

never exceeded the analytical detection limit 

of 10-8.5 M. Interestingly the pH values in 

the column studies showed significant 

variations between the two samples of slag 

material (Table 4-15). The higher pH values 

for slag sample two are consistent with the 

batch results for site A samples. The shorter 

analysis times for these samples, only 

approximately ten pore volumes, apparently 

prevented any significant introduction of 

atmospheric CO2 into the samples as 

happened with Site A samples in the column

study. The pH values are all higher than the 

influent river water, Table 4-5, used in the 

column studies. There was no correlation 

between the pH values and the dissolved Ca 

concentrations observed in the column 

effluents which ranged from 27 to 74 mg/l. 

The Ca concentrations were all as high or 

higher than the influent river water (Table 4-

5). 

36
Results and Discussion 

-9

-8

-7

-6

-5

-4

024 6 8 10 1

log Th or U (M)

Pore Volumes

2

Sample 1 - Th

Sample 2 - Th

Sample 1 - U

Sample 2 - U

Detection Limit

Figure 4-18. Thorium and uranium concentrations in Site C Column Studies.

Table 4-15. pH values in column studies from slags at Site C.

Pore Volumes Sample 1 Sample 2

4.09 10.67 

4.48 8.27 

7.42 9.88 

7.98 8.30 

10.4 10.85 

10.7 8.15 

4.3.3.2 URANIUM

Uranium solubilities in Site C samples, 

Figure 4-19, show very low solubilities in a 

similar fashion to the slag samples at Site B. 

In fact, the observed solubilities are even 

slightly lower than the values for either site 

A or site B (Figures 4-9 and 4-14 

respectively). Similarly, the U 

concentrations in the column studies, Figure 

4-18, correspond to the solubility studies. 

The uranium is most likely bound to the 

same type of refractory material as in Sites 

A or B (Table 4-4 and discussion). 

In summary, the solubility and column data 

for Site C show that the results for these 

slags show the same low solubilities for both 

Th and U observed for both Sites A and B.

37
Results and Discussion 

-10

-9

-8

-7

-6

-5

-4

-3

0 1 2 3 4 5 6 7 8 9 10 11 12 13

log U(M)

pH

Sample 1 - 4 days

Sample 1 - 13 days

Sample 2 - 4 days

Sample 2 - 13 days

Figure 4-19. Uranium concentrations in Site C Solubility Studies.

38
Calculations of Solubility Limits and Leaching Rates 

5 CALCULATIONS OF SOLUBILITY LIMITS AND LEACHING RATES 

This section presents calculations of the 

equilibration mass transfer (leaching) rates 

of Th and U from slags from Sites A, B, and 

C. These leaching rates were calculated 

using the highest observed dissolved 

concentration at the shortest equilibration 

time. This yielded the highest mass transfer 

rate for equilibration that can be calculated 

form the data. It is certainly possible that a 

higher transfer rate could have been 

calculated if samples were taken at earlier 

times (earliest times were 2hrs for batch 

data). Never the less, all of the samples 

reached equilibrium or at least steady state 

concentrations extremely rapidly since so 

little mass needed to be transfered to reach 

the steady state concentration. These 

calculations numerically demonstrate this 

fact. 

5.1 Site A 

Solubility controlled for both Th and U. Th 

- data from the coarse batch study were used 

(Figure 4-4), pH range (7-11). The highest 

solubility observed was 10-7.5M Th after 

2hrs contact time. The solution volume was 

30ml. This yields the following: 

- solubility = 3.2x10-8M 

- leaching rate = 1.1x10-7gTh/hr 1

U - data from the coarse batch study were 

used (Figure 4-9), pH range (7-11). The 

highest solubility observed was 10-7.6M U 

after 2hrs contact time. The solution volume 

was 30ml. This yields the following: 

 1

The leaching rates are calculated as 

follows: 

(3.2x10-8moles

Th/l)(.03l)(232gTh/mole)/2hrs.= 1.1x10-

7

gTh/hr. 

- solubility = 2.5x10-8M 

- leaching rate = 8.9x10-8gU/hr 2

5.2 Site B 

Solubility controlled for both Th and U. Th 

- data from the batch study were used 

(Figure 4-11), pH range (7-9). The highest 

solubility observed was 10-7.4M Th after 14 

days contact time. The solution volume was 

30ml. This yields the following: 

- solubility = 4x10-8M 

- leaching rate = 8.3x10-10

gTh/hr. 

U - data from the batch study were used 

(Figure 4-15), pH range (7-9). The highest 

solubility observed was 10-7.2M U after 7 

days contact time. The solution volume was 

30ml. This yields the following: 

- solubility = 6.3x10-8M 

- leaching rate = 2.7x10-9gU/hr. 

5.3 Site C 

Solubility controlled for Th. Th - data from

the solubility study were used (Figure 4-16). 

The highest solubility observed was 10-8.5M 

Th over the pH range (8-11). The shortest 

contact time was 4 days. The solution 

2

The leaching rates are calculated as 

follows: 

(2.5x10-8moles

U/l)(.03l)(238gU/mole)/2hrs.= 8.9x10-

8

gU/hr. 

39
Calculations of Solubility Limits and Leaching Rates 

volume was 30ml. This yields the 

following: 

- solubility = 3.2x10-9M 

- leaching rate = 2.3x10-10

gTh/hr. 

U - data from the solubility study were used 

(Figure 4-18), pH range (8-11). The highest 

solubility observed was 10-8.05 M U over the 

pH range (8-11). The shortest contact time 

was 4 days. The solution volume was 30ml. 

This yields the following: 

- solubility = 8.9x10-9M 

- leaching rate = 6.6x10-10

gU/hr. 

These results, converted to the units of g/cc 

for solubility limits and pCi/yr for release 

rate, are summarized in Table 5-1.

Table 5-1. Summary of Solubility and Leaching Rate Calculations at each Site. 

 Th U 

Site Solubility

Limit (g/cc)

Leaching Rate 

(pCi/yr)

Solubility 

Limit (g/cc)

Leaching Rate 

(pCi/yr)

Site A 7.4x10-9 100 6.0x10-9 260

Site B 9.3x10-8 1 1.5x10-8 8

Site C 7.4x10-10 0.2 2.0x10-9 2

40
Colloid Studies 

6 COLLOID STUDIES 

A comparison of filtered and unfiltered Th 

and U concentrations in the column studies 

at sites A and B (Table 6-1) did not show 

any evidence for the formation or transport 

of radiocolloids in any of the samples 

studied. 

Table 6-1. Filtered and unfiltered Th and U concentrations in column studies. UF - unfiltered, 

F - filtered. Pore size of filters approximately 0.0018um.

Site A 

 

 Site B

 (C-19) (C-21) 

Th - UF < 10-8.5

Analysis Site B

 < 10-8.5

Th - F < 10-8.5 < 10-8.5 < 10-8.5

U - UF < 10-8.5 < 10-8.5 10-8.2

U - F 10-8.5 10-8.3 10-8.1

 < 10-8.5

41
Colloid Studies 

42
Statistical Analysis 

7 STATISTICAL ANALYSIS 

Statistical analyses were performed on the 

batch, column, and solubility data for Th 

and U to better define the uncertainties 

involved in use of these data and for input to 

probabilistic site assessment models of 

radiological dose such as RESRAD (LePoire 

et al. 2000; Yu et al. 2000). Only the 

solubility data covering the range of 

expected pH values (7-10) were included in 

the analysis. For use of this data in 

probabilistic models, a known distribution 

and its parameters must be identified that 

best match the distribution of the actual 

values. In order to determine the nature of 

these distributions we began with the data 

from the batch studies 

7.1 Batch Studies (Sites A and B) 

The data sets from site B each comprised 30 

values, while the data from site A each had 

16. The behavior of the data is shown in 

Figure 7-1. 

0 2*10^-8 4*10^-8 6*10^-8 8*10^-8

0 2 4 6 8 10 12

Uranium

Frequency

0 2*10^-8 4*10^-8 6*10^-8

0 5 10 15 20

Thorium

Frequency

0 2*10^-7 4*10^-7 6*10^-7 8*10^-7

0 2 4 6 8 10 12

Uranium

Frequency

0 2*10^-7 4*10^-7 6*10^-7

0 2 4 6 8 10 12 14

Thorium

Frequency

Figure 7-1. Distributions of batch data for Th and U (moles/l). (a) Site B U. (b) Site B Th. (c) 

Site A U. (d) Site A Th.

43
Statistical Analysis 

As can be seen, much of the data fall in the 

area closer to zero. This is the expected 

behavior since many values were close to 

the analytical detection limit. Also, the data 

is quite sparse, so the task of defining a 

distribution and its parameters that best 

match the actual data becomes a somewhat 

difficult problem. There are several 

distributions from which to choose that this 

data could mimic. A Kolmogorov-Smirnoff 

(K-S) test was used to assess the data and its 

parameters for goodness of fit to the 

specified distribution. 

The K-S test assumes the hypothesis that the 

data in question is a certain distribution with 

specified parameters. The K-S statistic then 

collects the necessary information to

disprove the hypothesis by comparing the 

actual data to the hypothetical distribution. 

The K-S test can only show that the data is 

consistent with the proposed distribution. It 

cannot prove that the data fits this 

distribution. 

For the Site B data, a lognormal distribution 

was chosen with the following parameters: 

meanlog=-17.7 and sdlog=.57. The K-S 

statistic was K-S=.1667 and p-value=.808. 

Since the p-value is high (> .05), there is 

insufficient information to refute the claim

that the distribution is a lognormal with 

meanlog=-17.7 and sdlog=0.57. A plot of 

the actual data and the hypothetical data are 

shown in Figure 7-2.

0 2*10^-8 4*10^-8 6*10^-8 8*10^-8

0 2 468 10 12

Uranium

Frequency

0 2*10^-8 4*10^-8 6*10^-8 8*10^-8

024 6 8 10

Uranium

Frequency

Figure 7-2. Actual (a) and hypothesized (b) distributions of U concentrations (M) in batch 

experiments at site B. 

44
Statistical Analysis 

For the Site B thorium data, a lognormal 

distribution was also chosen with the 

following parameters: meanlog = -19.5 and 

sdlog=1.7. The K-S statistic was K-S = 0.2 

and p-value = 0.5941. This high p-value 

suggests there is not enough evidence to 

refute the claim of a lognormal distribution 

with meanlog=-19.5 and sdlog=1.7. A plot 

of the actual data and the hypothetical data 

are shown in Figure 7-3.

0 2*10^-8 4*10^-8 6*10^-8

0 5 10 15 20

Thorium

Frequency

0 2*10^-8 6*10^-8 10^-7 1.4*10^-7

0 5 10 15 20

Thorium

Frequency

Figure 7-3. Actual (a) and hypothesized (b) distributions of Th concentrations (M) in batch 

experiments at site B. 

For the Site A uranium data, a lognormal 

distribution was chosen with the same 

parameters as for site B (i.e. meanlog=-17.7 

and sdlog=.57). The K-S statistic was 0.375 

with a p-value of 0.2145. Since the p-value 

is high, there is insufficient information to 

refute the claim that the distribution is a 

lognormal with meanlog=-17.7 and 

sdlog=0.57. A plot of the actual data and 

the hypothetical data are shown in Figure 7-

4.

45
Statistical Analysis 

0 2*10^-7 4*10^-7 6*10^-7 8*10^-7

02468 10 12

Uranium

Frequency

0 2*10^-8 4*10^-8 6*10^-8

0 1 2345

Uranium

Frequency

Figure 7-4. Actual (a) and hypothesized (b) distributions of U (M) concentrations in batch 

experiments at site A. 

Similarily, for the Site A thorium data, a 

lognornal distribution was chosen with the 

same parameters as for site B (i.e. meanlog 

= -19.5 and sdlog=1.7. The K-S statistic 

was K-S = 0.25 and p-value = 0.7164. This 

p-value overwhelmingly suggests there is 

not enough evidence to refute the claim of a 

lognormal distribution with meanlog=-19.5 

and sdlog=1.7. This fact again supports the 

conclusion that the Th data are solubility 

controlled and the hence obey similar 

statistical distributions. A plot of the actual 

data and the hypothetical data is shown in 

Figure 7-5.

46
Statistical Analysis 

0 2*10^-7 4*10^-7 6*10^-7

0 2 4 6 8 10 12 14

Thorium

Frequency

0 5*10^-8 10^-7 1.5*10^-7

0 2 4 6 8

Thorium

Frequency

Figure 7-5. Actual (a) and hypothesized (b) distributions of Th concentrations (M) in batch 

experiments at site A. 

7.2 Column Studies (Sites A and B) 

1) Since the column study data had so 

few points, it is unreasonable to try 

to compare its distribution to a 

hypothetical one. Instead, a t-test 

was conducted to compare the means 

of each set of data (i.e. Site A and B, 

Th and U in the batch with the 

corresponding data for the columns) for 

a significant difference. 

All of these tests show a p-value above .05, 

which suggests there is not enough evidence 

to refute the claim that the data sets are 

equivalent. The graphs below (Figure 7-6) 

show each set of data on the same plot. 

47
Statistical Analysis 

Uranium

0 5 10 15 20 25 30

2*10^-8 6*10^-8

Thorium

0 5 10 15 20 25 30

0 2*10^-8 5*10^-8

Uranium

5 10 15

0 2*10^-7 6*10^-7

Thorium

5 10 15

0 2*10^-7 5*10^-7

Figure 7-6. Comparisons between site A and B batch and column data for Th and U. The 

darkened points are the column study data, while the clear points represent the batch 

data. (a) Site B uranium. (b) Site B thorium. (c) Site A uranium. (d) Site A thorium.

In summary, the distributional form of the 

batch data is the lognormal distribution, 

which can be input to probabilistic models 

of dose assessment. Furthermore, it appears 

the column study data are consistent with 

the measurements taken during the batch 

studies. 

7.3 Solubility Data (Sites A and B) 

Since the comparison of the column and 

batch data showed no significant 

differences, the data were combined and 

compared to the solubility data in the same

manner. All but one of these tests show a pvalue above .05, which suggests there is not 

enough evidence to refute the claim that the 

data sets are equivalent. Figure 7-7 shows 

each set of data on the same plot. 

48
Statistical Analysis 

Uranium

0 10 20 30 40 50

0 2*10^-8 6*10^-8

Thorium

0 10 20 30 40 50

0 2*10^-8 5*10^-8

Uranium

0 5 10 15 20 25 30

2*10^-8 6*10^-8 10^-7

Thorium

0 5 10 15 20 25 30

0 5*10^-9 1.5*10^-8

Figure 7-7. Comparisons between site A and B combined batch and column data with solubility 

data (pH 7-10) for Th and U. The darkened points are the batch and column study 

data, while the clear points represent the solubility data. (a) Site B uranium. (b) Site 

B thorium. (c) Site A uranium. (d) Site A thorium.

For the last test (site A thorium) , the pvalue=0.059, which is very close to being 

significant at the .05 level. From the plot, 

the darkened points look much more 

scattered than the clear points, which is 

probably why the t-test showed near 

significant differences between the data. 

Upon further investigation, the batch data 

contained the points causing the high scatter 

(see Figure 4-4). Never the less, these are 

the types of errors to be expected when 

measuring samples at such low 

concentrations even when the same

chemical phenomena (solubility) is probably 

responsible for the observed behavior. 

Hence, the need for probabilistic treatments 

of the data. 

7.4 Site C Comparison 

The solubility and column data from Site C 

samples were more limited than for Sites A 

or B. The Site C solubility data comprised 

29 values (pH range 7 –11 only included), 

while the column data comprised 6. As a 

result, only a t-test was done on these data. 

The results showed that these data could be 

explained by the same statistical parameters 

as the Th and U data at Sites A and B. A 

comparison between the column and 

solubility data is presented below.(Figures 

7-8, 7-9). 

49
Statistical Analysis 

0 2*10^-9 6*10^-9 10^-8

0 5 10 15

E

Thorium

Frequency

5*10^-11 1.5*10^-10 2.5*10^-10 3.5*10^-10

0.0 0.5 1.0 1.5 2.0

F

Thorium

Frequency

0 10^-8 2*10^-8 3*10^-8 4*10^-8

0 5 10 15 20 25

G

Uranium

Frequency

0 10^-8 2*10^-8 3*10^-8 4*10^-8

0 1 2 3 4

H

Uranium

Frequency

Figure 7-8. Comparisons between solubility and column data at Site C. (E) Thorium solubility 

data, (F) Thorium column data, (G) Uranium solubility data, (H) Uranium column

data. 

These tests show a p-value above .05, which 

suggests there is not enough evidence to 

refute the claim that the data sets are

equivalent. Each graph below (Figure 7-9) 

shows both sets of data on the same plot 

(thorium and uranium). The darkened points 

are the column study data, while the clear 

points represent the batch data. As can be 

seen, the number of column points is much 

less that that of the solubility data, which 

makes a thorough comparison more 

difficult. A visual inspection of these graphs 

show that the column data could easily be 

combined with the solubility data. 

50
Statistical Analysis 

EF

Thorium

0 5 10 15 20 25 30

0 2*10^-9 4*10^-9 6*10^-9 8*10^-9 10^-8

GH

Uranium

0 5 10 15 20 25 30

0 10^-8 2*10^-8 3*10^-8

Figure 7-9. Comparisons between the column and solubility data at Site C. (EF) Thorium data, 

(GH) column data. 

In summary, statistical analysis of the batch, 

column, and solubility data showed that the 

uncertainties in the dissolved Th and U 

concentrations can be described using a 

lognormal distribution with a meanlog of –

17.7 and a sdlog of 0.57 for U and a 

meanlog of –19.5 and an sdlog of 1.7 for Th. 

These parameters are valid for all three sites. 

51
Statistical Analysis 

52
References 

8 REFERENCES 

Allison, J.D., D.S. Brown, and K.J. NovoGradac (1991). MINTEQA2/PRODEFA2, 

A Geochemical Assessment Model for 

Environmental Systems (Version 3). 

UESPA, Environmental Research 

Laboratory, Athens GA (EPA/600/3-

91/021). 

Felmy, A.R., D. Rai, S.M. Sterner, M.J. 

Mason, N.J. Hess, and S.D. Conradson 

(1997). Thermodynamic Models for Highly 

Charged Aqueous Species: Solubility of 

Th(IV) Hydrous Oxide in Concentrated 

NaHCO3 and Na2CO3 Solutions. J. Solution 

Chem., 26(3), 233-248. 

Grenthe, I., J. Fuger, R.J.M. Konings, R.J. 

LeMire, A.B. Muller, C. Nguyen-Trung and 

H. Wanner (1992). Chemical 

thermodynamics of uranium, North-Holland, 

Elsevier Science Publishers, Amsterdam,

The Netherlands. 

Krupka, K.M. and R.J. Serne (1998). Effects 

on Radionuclide Concentrations by 

Cement/ground-Water Interactions in 

Support of Performance Assessment of 

Low-Level Radioactive Waste Disposal 

Facilities. NUREG/CR-6377. 

LePoire D., J. Arnish, E. Gnanapragasam, S. 

Kamboj, B.M. Biwer, J.-J. Cheng, C. Yu, 

and S.Y. Chen (2000). Probabilistic 

Modules for the RESRAD and RESRADBUILD Computer Codes – User Guide. 

NUREG/CR-6692 (ANL/EAD/TM-91). 

U.S. Nuclear Regulatory Commission, 

Washington, D.C. 

McKinley, J.P., J.M. Zachara, S.C. Smith, 

and G.D. Turner (1995). The Influence of 

Uranyl Hydrolysis and Multiple SiteBinding Reactions on Adsorption of U(VI) 

to Montmorillonite. Clays and Clay 

Minerals, 43(5), 586-598. 

Pickett, D.A., J.D. Prikryl, D.R. Turner, and 

J.L. Russell (1998). Evaluation of Leach 

Tests for Estimating Release from Slag Sites 

Subject to Decommissioning: Final Report. 

Center for Nuclear Waste Regulatory 

Analysis, San Antonio, TX. 

U.S. Nuclear Regulatory Commission 

(1995). Site Decommissioning Management 

Plan. NUREG-1444, Supplement 1. 

Washington, DC: Nuclear Regulatory 

Commission. 

Veblen, L.A., D.J. Farthing, K.J.T. Livi, 

D.R. Veblen, and E. O’Donnell (2001). 

Long Term Performance of Radioactive 

Slags - Characterization and Leach Rates. 

DRAFT NUREG/CR 1703, March 2001, 

U.S. Nuclear Regulatory Commission, 

Washington, D.C. 

Yu, C., D. LePoire, E. Gnanapragasam, J. 

Arnish, S. Kamboj, B.M. Biwer, J.-J. Cheng, 

and S.Y. Chen (2000). Probabilistic 

Modules for the RESRAD 6.0 and 

RESRAD-BUILD 3.0 Computer Codes. 

NUREG/CR-6697 (ANL/EAD/TM-98). 

U.S. Nuclear Regulatory Commission, 

Washington, D.C. 

53
References 

54
Appendix A 

APPENDIX A: EARLIER STUDIES OF SITE C SAMPLES 

Two sets of samples were sent to PNNL by 

staff at the Center for Nuclear Waste 

Regulatory Analyses (CNWRA), San 

Antonio TX. The first set containing six 

samples was received in December 1997 and 

the second set, consisting of two samples, 

was received in June 1998. The samples 

were scanned with a GM counter and the 

radioactive samples were analyzed by

gamma spectroscopy. 

A summary of the physical characteristics of 

the samples received in December 1997 is 

given in Table A1. Only two of the 

samples, WH-4 and WH-6, showed 

detectable radioactivity on the GM counter. 

Sample WH-6 was comprised of two types 

of material, an asphalt like material with 

embedded grayish white particles (sample 

A) and a pure grayish white material 

(sample B). These materials were separated 

and analyzed by gamma spectroscopy, Table 

A2. The grayish white material (sample B) 

proved to be essentially non-radioactive. 

All of the radioactivity apparently being 

concentrated in the asphalt like sample (A). 

Interestingly all of the radioactivity in the 

asphalt like material is due to Th-232 or its 

daughters. This is in contrast to sample 

WH-4 which also shows U-238 daughters. 

The materials also appear to be reasonably 

homogeneous as different sub samples of the 

materials give similar radiological analyses. 

A alpha spectra for sample WH-4 is shown 

in Figure A-1. 

Radiological analyses of the sample 

received in June 1998, Table A3, show these 

materials to be essentially non-radioactive.

Table A1. Physical characteristics of samples received in December 1997. 

Sample Weight (Kg) Description GM Activity(dpm) 

WH-1 1.976 Black/green or grayish slag none 

WH-2 1.150 Blue/green to dark green slag none 

WH-3 0.743 2 pieces of 

blackish/gray/green slag, one 

piece of gray slag 

none 

WH-4 0.823 Dark black ash 2,500 

WH-5 1.312 Numerous small pieces, 

grayish brown rock – light 

white/gray material 

none 

WH-6 0.909 Two types of material, 

asphalt like with embedded 

gray/white particles (A), pure 

grayish white material (B) 

10,000 

A-1
Appendix A 

Table A2. Radiological analysis of slags at Site C (December 1997). Values in parentheses 

under the sample designation represent counts of different subsamples. Values in pCi/g. 

WH-4

(1) 

WH-4

(2) 

WH-6 (A) 

(1) 

WH-6 (A) 

(2) 

WH-6 (A) 

(3) 

WH-6 (B) 

(1) 

WH-6 (B) 

(2) 

Th-232 

Series 

Ac-228 27 30 146 151 167 nd nd

Bi-212 31 33 152 nd 180 nd nd

Pb-212 27 30 149 160 167 <1 <1

Ra-224 nd nd nd 166 170 nd 2

U-238 

Series 

Ra-226 16 17 nd nd nd 1 <1

Bi-214 12 14 nd nd nd <1 <1

Pb-214 14 15 nd nd nd <1 <1

Table A3. Radiological analysis of slags at Site C (June 1998). Values in pCi/g. 

W2 W3a 

Th Series 

Ac-228 1 <1

Bi-212 3 <1

Pb-212 2 <1

Ra-224 nd 1

U-238 

Series 

Ra-226 3 nd

Bi-214 3 <1

Pb-214 3 <1

A-2
Appendix A 

 

 

Th-230 

Po-216 

Rn-220 

Ra-224 

Th-228 

Th-232 

Figure A-1. Alpha spectra for sample WH-4. 

A-3
Appendix A 

A-4
Appendix B 

APPENDIX B: TABLES OF EXPERIMENTAL DATA. 

Table B1. Data Supporting Figure 4-4. 

pH 

log Th 

4 days 

log Th 

31 days 

log Th 

275 days 

0.75 -4.93

1.24 -5

1.7 -5.44

2.27 -6.38

3.14 -7.56

3.18 -7.13

3.31 -7.36

3.55 -7.64

3.57 -7.88

3.61 -7.94

4.1 -8.13

4.31 -7.56

4.54 -8.32

4.78 -8.5

5.52 -8.5

6.19 -8.5

6.37 -8.17

6.66 -8.5

6.88 -8.5

7.19 -8.5

7.77 -8.5

8.01 -8.5

8.11 -8.5

8.49 -8.5

8.56 -8.5

8.66 -8.5

9 -8.5

9.01 -8.12

9.24 -8.5

9.53 -8.5

9.65 -8.5

9.76 -8.5

10.11 -8.5

10.16 -8.5

10.19 -8.5

10.64 -8.5

10.78 -8.5

11.02 -8.5

11.45 -8.5

11.56 -8.5

12.01 -8.5

12.12 -8.5

12.24 -8.5

B-1
Appendix B 

Table B2. Data Supporting Figure 4-5. 

Days

log Th 

4 days 

Fine Material 

log Th 

31 days 

Coarse Material 

(Sample A)

log Th 

275 days 

Coarse Material 

(Sample B) 

0.08 -6.9 -8.08 -7.53

0.25 -7.86

3 -8.5 -7.48 -7.87

7 -8.5 -7.71 -7.52

14 -7.45

15 -7.83

37 -7.6

45 -7.8 -7.82

Table B3. Data Supporting Figure 4-6. 

Days

Th 

Log(moles/L)

U 

Log(moles/L)

4 -8.5 -8.03

11 -8.5 -8.12

30 -8.5 -7.88

Table B4. Data Supporting Figure 4-7. 

pH

log Ca(M) 

4 days 

log Sr(M) 

31 days 

log Ba(M) 

275 days 

1.57 -1.4 -4.16 -2.28

3.49 -1.41 -4.15 -2.29

3.84 -1.37 -4.1 -2.24

5.87 -1.45 -4.28 -2.39

7.54 -1.39 -4.19 -2.45

8.02 -1.7 -4.48 -2.78

8.93 -2.06 -4.59 -2.97

9.41 -2.23 -4.66 -3.09

10 -2.34 -4.74 -3.38

10.4 -2.52 -4.9 -3.66

11.14 -2.93 -5.24 -4.18

12.12 -4.21 -6.16 -5.01

B-2
Appendix B 

Table B5. Data Supporting Figure 4-9. 

pH

log U 

4 days 

log U 

31 days 

0.75 -6.08

1.24 -6.05

1.7 -6.03

2.27 -6.19

3.14 -6.23

3.18 -6.2

3.55 -6.7

3.57 -6.34

4.1 -6.54

4.31 -6.88

4.78 -7.31

5.52 -6.87

6.19 -7.04

6.37 -7.13

6.66 -7.05

6.88 -7.12

7.77 -7.04

8.11 -7.19

8.49 -7.22

8.66 -7.28

9 -7.37

9.01 -7.14

9.53 -7.49

9.76 -7.32

10.11 -6.93

10.19 -7.1

10.64 -7.11

11.02 -6.97

11.45 -7.14

12.01 -7.27

12.24 -7.08

 

Table B6. Data Supporting Figure 4-10. 

Days

log U(T)

Fine Material 

4 days 

log U(T)

Coarse Material 

(Sample A)

31 days 

log U(T)

Coarse Material 

(Sample B) 

275 days 

0.08 -6.73 -7.81 -7.5

0.25 -6.11

3 -6.44 -7.7 -7.68

7 -6.72 -7.7 -7.6

14 -7.63 -7.63

15 -6.87

37 -6.55

45 -7.66 -7.77

B-3
Appendix B 

Table B7. Data Supporting Figure 4-11. 

pH

log Th 

C9 - 5 Days 

log Th 

C9 - 113 Days 

log Th 

C19 - 5 Days 

log Th 

C19 - 113 Days 

log Th 

C1000 - 5 Days 

log Th 

C1000 - 106 Days

0.7 -4.52

0.75 -4.31

0.86 -4.18

1.15 -6.39 -5.74

1.8 -6.51

2.12 -4.85

 2.23 -7.33 

2.32 -7.4

2.97 -5.79

3.05 -8.15

3.11 -8.5

3.55 -7.83

3.7 -6.96

3.78 -7.53

3.98 -6.46

4.03 -7.39

4.08 -6.7

4.33 -8.56

4.44 -8.5

4.61 -7.69

4.82 -7.48

4.86 -8.21

5.02 -8

5.03 -8.21

5.11 -8.5

5.51 -8.5

5.62 -8.03

5.63 -7.92

5.69 -8.5

5.84 -8.29

5.98 -8.31

6.1 -8.54 -6.54

6.2 -8.5

6.25 -7.96

6.33 -8.5

6.44 -7.76

6.54 -7.62

6.65 -8.01

6.85 -8.5

6.92 -8.29

6.95 -8.42

6.99 -8.5

7.01 -8.27

7.03 -8.07

7.13 -8.52

7.16 -8.5

7.21 -8.14

7.47 -7.74

7.6 -8.5

7.62 -7.73

7.72 -8.36

8 -8.04

8.04 -8.53

8.08 -8.41

8.11 -8.23

8.19 -8.05

8.28 8.5

8.48 -8.5

8.5 -8.5

8.57 -8.5

8.66 -8.5

B-4
Appendix B 

Table B7 (Continued). Data Supporting Figure 4-11. 

pH

log Th 

C9 - 5 Days 

log Th 

C9 - 113 Days 

log Th 

C19 - 5 Days 

log Th 

C19 - 113 Days 

log Th 

C1000 - 5 Days 

log Th 

C1000 - 106 Days

8.75 -8.26

8.77 -8.5

8.83 -8.01 8.5

8.93 -7.97

8.96 -8.5

8.98 -8.5

9.14 -7.83

9.33 -8.5

9.59 -8.5

9.63 -8.5

9.66 -7.84

9.68 -8.5

9.72 -8.5

10.03 -8.01

10.14 -8.5

10.31 -8.5

10.37 -8.06

11.48 -8.5

10.65 -7.56

10.72 -8.45

10.96 -8.5

11.01 -7.97

11.29 -8.5

11.39 -7.2

11.44 -7.97

11.46 -8.5

11.49 -7.74

11.57 -8.5

12 -8.5

12.05 -8.5

12.1 -8.02

12.13 -8.5

Table B8. Data Supporting Figure 4-12. 

Days

log Th 

C9 Sample 1 

log Th 

C9 Sample 2 

log Th 

C19 Sample 1 

log Th 

C19 Sample 2 

log Th 

C20 Sample 1 

log Th 

C20 Sample 2 

0.08 -8.44 -8.38 -8.48 -8.5 -8.5 -8.5

3 -8.28 -8.5 -8.5 -8.33 -8.5 -8.5

7 -8.13 -8.5 -7.75 -8.2 -8.13 -7.46

14 -7.22 -8.02 -8.41 -7.49 -8.34 -8.48

45 -8.1 -8.03 -7.7 -7.24 -8.5 -7.51

Table B9. Data Supporting Figure 4-13. 

Pore Volumes

Th 

Log(moles/L)

U 

Log(moles/L)

10.29 -8.5 -8.23

14.95 -8.5 -7.24

70.92 -8.5 -8.0

B-5
Appendix B 

Table B10. Data Supporting Figure 4-14. 

pH

log U(T)

C9 - 5 Days 

log U(T)

C9 - 113 Days 

log U(T)

C19 - 5 Days 

log U(T)

C19 - 113 Days 

log U(T)

C20 - 5 Days 

log U(T)

C20 - 106 Days 

0.7 -4.89

0.75 -4.76

0.86 -5.47

1.15 -5.27 -5.28

1.8 -5.72

2.12 -6.46

 2.23 -6.33 

2.32 -5.94

2.97 -7.22

3.05 -6.71

3.11 -6.02

3.55 -7.2

3.7 -7.08

3.78 -7.06

3.98 -7.3

4.03 -7.56

4.08 -6.99

4.33 -7.08 -7.08

4.44 -7.29

4.61 -7.26

4.82 -7.33

4.86 -7.71

5.02 -7.49

5.03 -7.57

5.11 -7.78

5.51 -8.36

5.62 -7.29

5.63 -7.23

5.69 -8.5

5.84 -7.28

5.98 -8.36

6.1 -7.77 -8.5

6.2 -7.97

6.25 -7.41

6.33 -7.99

6.44 -7.27

6.54 -7.52

6.65 -7.59

6.92 -7.36

6.95 -8.03

6.99 -8.04

7.01 -7.83

7.03 -7.18

7.13 -8.62

7.16 -8.5

7.21 -7.92

7.47 -7.32

7.6 -8.33

7.62 -7.45

7.72 -7.38

8 -7.23

8.04 -7.33

8.08 -7.89

8.11 -8.5

8.19 -8.19

8.28 -7.4

8.48 -8.54

8.5 -8.03

8.57 -8.44

8.66 -8.5

8.75 -8.12

8.77 -8.29

B-6
Appendix B 

Table B10 (Continued). Data Supporting Figure 4-14. 

pH

log U(T)

C9 - 5 Days 

log U(T)

C9 - 113 Days 

log U(T)

C19 - 5 Days 

log U(T)

C19 - 113 Days 

log U(T)

C20 - 5 Days 

log U(T)

C20 - 106 Days 

8.83 -7.24 -7.26

8.93 -7.06

8.96 -8.47

8.98 -7.52

9.14 -7.65

9.33 -8.38

9.59 -8.51

9.63 -8.17

9.66 -8.01

9.68 -8.37

9.72 -7.5

10.03 -8.09

10.14 -7.89

10.31 -7.68

10.37 -8.1

11.48 -8.5

10.65 -8.19

10.72 -7.4

10.96 -8.15

11.01 -8.08

11.29 -7.34

11.39 -7.34

11.44 -7.99

11.46 -8.37

11.49 -8.35

11.57 -7.9

12 -8.18

12.1 -7.84

12.13 -7.36

Table B11. Data Supporting Figure 4-15. 

pH

log Ca(T) 

Site A 

log Ca(T) 

Site C(C-9)

1.15 -1.72

1.57 -1.4

1.8 -1.76

3.49 -1.41

3.84 -1.37

4.03 -2.18

5.02 -2.37

5.84 -2.62

5.87 -1.45

7.47 -2.87

7.54 -1.39

8.02 -1.7

8.93 -2.06

9.41 -2.23

9.66 -4.08

10 -2.34

10.4 -2.52

10.65 -4.4

11.14 -2.93

12.12 -4.21

B-7
Appendix B 

Table B12. Data Supporting Figure 4-16. 

Days

log U(T)

C-9 Sample 

1 

log U(T)

C-9 

Sample 2 

log U(T)

C-19 

Sample 1 

log U(T)

C-19 

Sample 2 

log U(T)

C-20 

Sample 1 

log U(T)

C-20 Sample 

2 

log U(T)

C-9 

(CO2) 

log U(T)

C-20 

(CO2) 

0.08 -7.6 -8.02 -7.68 -7.7 -7.78 -7.86 -8.5 -8.5

3 -7.84 -7.94 -7.86 -7.7 -7.77 -7.52 -7.87 -8.5

7 -7.4 -7.99 -7.11 -7.26 -7.32 -7.46 -7.6 -8.1

14 -7.21 -7.73 -7.68 -7.53 -7.53 -7.12 -7.5 -8.4

45 -7 .6 -7.55 -7.71 -7.76 -8.03 -7.87 -7.5 -8.1

Table B13. Data Supporting Figure 4-17.

pH 

Sample 1 - 4 days pH Sample 1 - 13 days pH Sample 2 - 4 days pH Sample 2 - 13 days 

5.09 -8.5 6.01 -8.5 1.12 -5.09 1.89 -5.03

3.99 -8.5 4.14 -8.5 3.42 -6.8 4.32 -7.43

5.01 -8.5 5.72 -8.5 4.08 -7.64 5.62 -8.13

5.61 -8.5 6.53 -8.5 5.67 -8.16 9.15 -8.5

5.91 -8.5 7.05 -8.5 8.19 -8.37 9.94 -8.5

6.72 -8.5 6.99 -8.5 8.85 -8.5 10.24 -8.5

7.21 -8.5 7.4 -8.39 9.22 -8.5 9.85 -8.5

7.58 -8.5 7.44 -8.41 9.85 -8.5 10.21 -8.5

7.65 -8.48 7.6 -8.3 10.23 -8.5 10.73 -8.5

9.32 -8.5 8.17 -8.37 10.42 -8.5 10.36 -8.5

10.55 -8.47 8.84 -7.99 10.78 -8.5 10.78 -8.5

11.93 -8.5 12 -7.78 11.72 -8.5 11.69 -8.5

1.32 -5.98 1.32 -5.86 4.92 -7.47 7.21 -8.5

6.29 -8.5 7.2 -8.5 6.47 -7.99 9.07 -8.5

Table B14. Data Supporting Figure 4-18.

Pore Volumes 

Th 

Log(moles/L)

Sample 1 

Th 

Log(moles/L)

Sample 2 

U 

Log(moles/L)

Sample 1 

U 

Log(moles/L)

Sample 2 

4.48 -8.5 -7.47

7.98 -8.5 -8.5

10.7 -8.5 -8.05

4.09 -8.5 -8.5

7.42 -8.5 -7.85

10.4 -8.5 -8.5

Table B15. Data Supporting Figure 4-19.

pH Sample 1 - 4 days pH Sample 1 - 13 days pH Sample 2 - 4 days pH Sample 2 - 13 days 

5.09 -8.5 6.01 -8.5 1.12 -6.12 1.89 -6.04

3.99 -7.63 4.14 -8.18 3.42 -7.14 4.32 -7.56

5.01 -8.5 5.72 -8.5 4.08 -7.62 5.62 -8.5

5.61 -8.5 6.53 -8.5 5.67 -8.5 9.15 -8.5

5.91 -8.5 7.05 -8.5 8.19 -8.5 9.94 -8.5

6.72 -8.5 6.99 -8.5 8.85 -8.5 10.24 -8.5

7.21 -8.5 7.4 -8.48 9.22 -8.5 9.85 -8.5

7.58 -8.5 7.44 -8.49 9.85 -8.5 10.21 -8.5

7.65 -8.47 7.6 -8.38 10.23 -8.5 10.73 -8.5

9.32 -8.35 8.17 -8.05 10.42 -8.5 10.36 -8.5

10.55 -8.05 8.84 -7.43 10.78 -8.5 10.78 -8.5

11.93 -7.31 12 -7.22 11.72 -8.5 11.69 -8.5

1.32 -6.05 1.32 -5.99 4.92 -7.96 7.21 -8.5

6.29 -9.3 7.2 -8.5 6.47 -8.5 9.07 -8.5

B-8
Appendix C 

APPENDIX C: 

Thermodynamics of the U(VI)-Ca2+-Cl-

-OH--H2O 

System: Solubility Product of Becquerelite 

Dhanpat Rai 

Andrew R. Felmy 

Nancy J. Hess 

Virginia L. LeGore 

David E. McCready 

Pacific Northwest National Laboratory 

Richland, WA 99352 USA 

C-1
Appendix C 

Thermodynamics of the U(VI)-Ca2+-Cl-

-OH--H2O System: 

Solubility Product of Becquerelite 

Dhanpat Rai, Andrew R. Felmy, Nancy J. Hess, Virginia L. LeGore, and 

David E. McCready 

Pacific Northwest National Laboratory, Richland, WA 99352

Summary 

The solubility of synthetic becquerelite (Ca(UO2)6O4(OH)6•8H2O) was determined in 0.02, 0.1, 

and 0.5 M CaCl2 solutions and at pCH+ values ranging from approximately 4 to 11. The 

presence of becquerelite in equilibrated samples was confirmed by a combination of techniques 

involving X-ray diffraction, total chemical composition, and analyses of solubility data. The 

solubility data were interpreted using Pitzer’s aqueous thermodynamic model and the 

thermodynamic data for U(VI) species available in the literature. The log of the solubility 

product for becquerelite [Ca(UO2)6O4(OH)6•8H2O + 14H+

 = Ca2+ + 6UO2

2+ + 18H2O] was 

determined to be 41.4±0.2. This value is similar to the values previously reported for other 

synthetic becquerelite samples, but is drastically different than a value reported for a natural 

sample. These data were used to interpret the observed U(VI) concentrations in solutions 

obtained from suspensions in water of U contaminated soils and slags collected from SDMP 

sites as discussed in the previous sections. 

Key Words: Thermodynamics, becquerelite, solubility, solubility product, hexavalent 

uranium, uranium

C-2
Appendix C 

Introduction 

Uranium is one of the important constituents in the nuclear fuel cycle, in nuclear wastes, and in 

decommissioned nuclear facilities. In geologic environments, U exists primarily in the 

tetravalent and hexavalent states. Uranium in the tetravalent state readily forms hydrous oxide 

that has low solubility [1-3] and thus is not readily transported in subsurface groundwater. 

However, hexavalent U compounds (e.g., schoepites) are very soluble, and U(VI) forms strong 

complexes with hydroxide and carbonates [4], the most common ligands in geologic 

environments, making the hexavalent form the most mobile state in groundwater. However, in 

the presence of alkali and alkaline earth cations, common groundwater ions, U(VI) can 

precipitate as relatively insoluble compounds, making U(VI) far less soluble and potentially 

less mobile [4]. A recent review of the thermodynamic data [4] shows that reliable data for 

most of these compounds are not available. One of the reasons for this lack of reliable data is 

that a large number of compounds could possibly form with a given cation, making 

identification of the solubility-controlling phase difficult. For example, several of the 

compounds that could form in the presence of Ca, a ubiquitous cation in groundwater, are 

Ca(UO2)6O4(OH)6•8H2O, Ca2UO5(H2O)1.3-1.7, CaUO4, Ca3UO6, CaU2O7 [5]. 

Members of the becquerelite structural group [becquerelite, Ca(UO2)6O4(OH)6•8H2O; and 

compreignacite, K2(UO2)6O4(OH)6•8H2O] have been identified in uraninite alteration products 

[6] and in oxidative corrosion of synthetic UO2(s) [7,8a], and becquerelite itself is known to form

from schoepite in nature. Becquerelite also appears to be an important phase in cementicious 

environments [5]. Uranium dioxide alteration phases including becquerelite may also form

C-3
Appendix C 

during spent fuel alteration [8b]. Even though becquerelite appears to be a geologically 

important mineral, only limited experimental data have been reported for this phase [5, 9-11], 

and the reported solubility products vary over 12 orders of magnitude. To obtain reliable 

thermodynamic data for becquerelite that is applicable to a wide range in environmental 

conditions, experimental solubility data are required over a wide range of pH values and Ca 

concentrations. However, the available data lack these attributes. Examples include Atkins et al.

[5], who reported solubilities of becquerelite in distilled water or in 0.5 M NaOH; they do not 

report pH or Ca concentrations, and thus no thermodynamic data can be obtained from their 

study. Vochten and Van Haverbeke [9] reported a solubility product of this compound based on 

a limited number of samples equilibrated only in water; they do not report Ca concentrations. 

Sandino and Grambow [10] studied the solubility of becquerelite (Ca(UO2)6O4(OH)6•8H2O) at 

only one Ca concentration (1.0 M CaCl2) and three groups of selected pH values, and their 

reported ranges in solubility product values vary by about three orders of magnitude. Casas et al.

[11] based their study on a naturally occurring becquerelite suspended in water and adjusted to 

four different pH values at different times. They calculated log K0

 of 29±1 for 

(Ca(UO2)6O4(OH)6•8H2O + 14H+

 = Ca2+ + 6UO2

2+ + 18H2O), which differed by over 12 orders 

of magnitude from the values (41.89 to 43.6) determined by Vochten and Van Haverbeke [9] 

and by Sandino and Grambow [10]. Clearly, reliable thermodynamic data for becquerelite are 

not available. Therefore, this study was undertaken and we determined solubilities of 

becquerelite in 0.02, 0.1, or 0.5 M CaCl2 solutions ranging in pCH+ values from 4.4 to 11.4 using 

numerous samples that were analyzed at several equilibration periods. The data obtained in this 

study were then used to interpret U(VI) behavior in U contaminated soils and slags from selected 

SDMP sites (see main body of this report for these details). 

C-4
Appendix C 

Methods and materials 

Reagents 

All solutions were prepared with deionized water that was degassed by boiling and cooling in 

an N2 (99.99%) atmosphere. 

For precipitating becquerelite, a 0.1 M stock solution of Ca was prepared from Ca(NO3)•4H2O 

(Aldrich Products) and a solution of U(VI) from UO2(NO3)2 (Mallinckrodt). Stock solutions 

(0.02, 0.1, and 0.5 M) of Ca for equilibrium solubility studies were prepared from CaCl2

(Aldrich). Tetraethyl ammonium hydroxide (25%) was obtained from Kodak Chemicals and 

was used for adjusting pH values to avoid introduction of other alkali or alkaline earth cations 

into the equilibrating solutions. 

Becquerelite [Ca(UO2)6O4(OH)6•8H2O, or stoichiometrically represented as CaU6O19•11H2O] 

was prepared in a fashion similar to that described by Sandino and Grambow [10]. Briefly, 

uranyl and calcium nitrate stock solutions were mixed together in 50-mL plastic tubes in 

stoichiometric proportions (1:6 molar concentrations of Ca and U, respectively) at room 

temperature to obtain becquerelite solid containing approximately 107 mg of U(VI) in each 

tube. The pH value of the mixture was adjusted to about 4.5 with tetraethylammonium

hydroxide to precipitate the solid. The precipitates were aged in mother liquor for 21 days. At 

the end of this period, the suspensions were centrifuged, and the supernatant was discarded. 

The precipitates were then washed with deionized-degassed water. 

C-5
Appendix C 

Experimental procedures 

 

All experiments were conducted in an atmosphere-controlled chamber with a prepurified N2

atmosphere (99.99% N2, with <10 ppm O2) and at 22±2°C. The solubility in all experiments 

was approached from the undersaturation direction. Three sets of experiments were conducted 

with the washed precipitates. These sets contained 0.02, 0.1, or 0.5 M CaCl2. A 30-mL volume 

of appropriate solution was added to the washed precipitates in centrifuge tubes. The pH 

values of these samples were adjusted to a range between 4.4 and 11.4 using HNO3 or 

tetraethylammonium hydroxide. The tubes were capped tightly and placed on a shaker.

Periodically, the pH values of the suspensions were measured with an Orion-Ross combination 

glass electrode calibrated against pH buffers. The pH meter readings were converted to 

hydrogen ion concentrations using a modified Gran titration procedure [12]. In the Gran 

titration method, the observed/measured pH [pH(obs)] is related to the concentration of 

hydrogen ions by the equation (pCH+ = pH(obs) + A), where pCH+ is the negative logarithm of

hydrogen ion concentration in molarity units, and A is a constant. The values of A for 0.02, 

0.1, and 0.5 M CaCl2 solutions were determined to be 0.134, 0.161, and 0.283, respectively, 

using the procedure described by Rai et al. [12]. 

At different equilibration periods, the suspensions were centrifuged at 2000 g for 10 to 15 

minutes. The supernatant was filtered through Amicon Centriflo cones (Amicon Corp.) with a 

25,000 molecular-weight cutoff and approximately 0.0018-μm pore size. Prior to use, the 

filters were washed with deionized water followed by deionized water adjusted to the pH value 

C-6
Appendix C 

of a given sample. A 2.0-mL sample solution was passed through the filters and the filtrate 

discarded before the actual sample solution was filtered. The filtrate was acidified with HNO3, 

and the concentrations of U were determined by inductively coupled plasma mass 

spectroscopy. All of the solubility data are reported in the Appendix (Tables A.1 through 

A.3). At the end of the study, the solid samples were separated and analyzed for crystallinity 

by X-ray diffraction using Cu Kα radiation. 

X-ray absorption spectroscopy experiments were conducted at Stanford Synchrotron Radiation 

Laboratory (beamline 4-2). Spectra were collected at the U LIII -edge in fluorescence mode 

using a 13-element Ge detector. All spectra were measured to a photoelectron wave vector of 

13 Å-1. Energy calibration was based on assigning the first inflection point of the absorption 

edge of a Zr standard to 17999.35 eV. Normalization of the absorption spectrum and 

extraction of the extended X-ray absorption fine structure were performed following standard 

procedures described in Rai et al. [13]. 

Thermodynamic model 

The ion-interaction model of Pitzer and co-workers [14, 15] was used to interpret solubility 

data. This aqueous thermodynamic model emphasizes a detailed description of the specific ion 

interactions in solution. The effects of specific ion interactions on the excess solution free 

energy are contained in the expressions for the activity coefficients. The activity coefficients 

can be expressed in a virial-type expansion as 

C-7
Appendix C 

ln = ln + (I)m + C m m + ... (1) ijk j k

j k

ij j

j

DH γi γi ∑ β ∑ ∑

where m is the molality, γi

DH is a modified Debye-Hückel activity coefficient that is a universal 

function of ionic strength, and βij(I) and Cijk are specific for each ion interaction and are 

functions of ionic strength. The third virial coefficient, C, is understood to be independent of 

ionic strength. A detailed description of the exact form of Eq. (1) is published in Felmy and 

Weare [16] and Felmy et al. [17] and is contained in the nonlinear least-squares program

(NONLIN, developed by A. R. Felmy) for estimating activity coefficients and calculating 

chemical equilibria involving multiple solid and aqueous species. NONLIN has been used 

extensively for interpreting data similar to those obtained in this study [17-20]. For 

interpreting the present solubility data, no attempt was made to convert molarity units to the 

molality units needed for modeling because even at the highest CaCl2 concentrations used in 

these experiments (0.5 M) the error introduced by neglecting this conversion is almost 

negligible (1.2%), and it would be even more negligible at the lower CaCl2 concentrations. 

In terms of evaluating the aqueous species present in solution, we used the standard state 

equilibrium constants for the U(VI) species recently summarized by Grenthe et al. [4]. 

C-8
Appendix C 

Results and Discussion 

Observed Solubility 

The observed aqueous U concentrations plotted as a function of pCH+, CaCl2 concentrations, 

and equilibration period (Figures 1 through 3) in general indicate that the U concentrations: 1) 

decrease approximately two orders of magnitude with one unit increase in pCH+ at all CaCl2

concentrations below pCH+ of ~7 and appear to be nearly constant between pCH+ 7 and 12, 2) 

are similar at different equilibration periods for different CaCl2 concentrations, indicating that 

steady-state concentrations are reached rapidly (<4 days), and 3) appear to be similar in 

different CaCl2 concentrations (Figure 4). 

Characterization of Solubility-Controlling Phase 

A combination of techniques including preparation of the solid phase using a procedure 

recommended by Sandino and Grambow [10], X-ray diffraction (XRD), X-ray absorption 

spectroscopy (XAS), total chemical composition, and thermodynamic modeling of the 

solubility data were used to identify the solubility-controlling phase in these experiments. It 

was necessary to use a combination of techniques because of the difficulties involved in 

characterizing the phase when only one characterization technique was used. These difficulties 

arise from the fact that most alkali metal and alkaline earth hydrated U(VI) solids have similar 

chemical compositions and structures, making it difficult to unequivocally state the presence of 

only one phase. 

C-9
Appendix C 

X-ray Diffraction and Total Chemical Composition Analyses 

Sandino and Grambow [10] have shown that, in the presence of Ca and at pCH+ ~4, uranyl 

hydroxide transforms quickly to becquerelite at room temperature. Therefore, we followed 

their procedure to prepare the solid phase used in this study. Atkins et al. [5] showed that in 

highly alkaline systems (pH ~12), in the presence of Ca(OH)2, two Ca phases are expected, 

Ca(UO2)6O4(OH)6•8H2O and Ca2UO5(H2O)1.3 -1.7, with the latter being favored. X-ray 

diffraction analyses of the equilibrated phases at pCH+ between 4.3 and 8.0 (Table 1, Figure 5) 

show the presence of becquerelite as the major phase, along with the presence of other minor 

unaccounted peaks for solids that appear to increase in concentration with the increase in pCH+. 

These results are similar to the total chemical analyses of the solid phases (Table 2), showing 

molar U/Ca ratios at pCH+ values <8 that are similar to the theoretical values for becquerelite 

(6:1), but the ratios decrease to around 2 at pCH+ >8. We also noted that the color of the 

precipitate changed noticeably at pCH+ values around 11, indicating a significant change in the 

dominant solid phase at higher pCH+ values consistent with the XRD analyses, which did not 

detect the presence of becquerelite. Nevertheless, these total chemical composition data 

suggest that the dominant phase is becquerelite at pCH+ <~8, but the presence of other minor 

phases cannot be ruled out. 

Sandino and Grambow [10] showed that alkali and alkaline earth compounds are readily 

formed from uranyl hydroxide at room temperature. Although a number of U(VI)-Ca phases 

(e.g., Ca(UO2)6O4(OH)6•8H2O, Ca2UO5(H2O)1.3-1.7, CaUO4, Ca3UO6, and CaU2O7) can form in 

the alkaline environment, the data of Atkins et al. [5] show that Ca(UO2)6O4(OH)6•8H2O and 

C-10
Appendix C 

Ca2UO5(H2O)1.3-1.7 are the most likely phases. It can be noted that all of the other possible 

U(VI)-Ca solids have lower U/Ca ratios than becquerelite. The U/Ca molar ratio for CaUO4 is 

1:1 and for Ca2UO5(H2O)1.3-1.7 is 1:2 as compared with 6:1 for becquerelite. The observed 

lower U/Ca molar ratios (Table 2) at pH >8 are consistent with the formation of such 

compounds. 

X-ray Absorption Spectroscopic Analyses 

Definitive identification of the solubility-limiting phase using analysis of the XAS spectra was 

not possible because of the structural similarity of hydrated Ca-U(VI) phases. All samples 

analyzed (pCH+ 5.93, 0.02 M CaCl2; pCH+ 6.18, 0.5 M CaCl2; and pCH+ 7.56, 0.1 M CaCl2) 

displayed virtually identical X-ray absorption near edge structure (XANES) indicative of a 

U(VI) oxidation state and similar features in the Fourier analysis of the extended x-ray 

absorption fine structure (EXAFS) shown in Figure 6. Fits to the EXAFS reveal the number of 

atoms and the interatomic distances to about 4.0 Å, which varied from sample to sample, but 

could not be used to unequivocally identify the predominant hydrated Ca-U(VI) phase. 

Solubility Data Analyses

Although becquerelite is clearly the primary phase present in our samples (XRD and total 

chemical composition) at pCH+ values <8, this does not mean that it is the solubility-controlling 

solid. To better assess this situation we turn to an initial analysis of the solubility data. 

C-11
Appendix C 

Reliable thermodynamic data for calculating the solubility of Ca uranates are available only for 

CaUO4. Comparison of the predicted CaUO4(c) solubility in 0.1 M CaCl2 using the 

thermodynamic data reported in Grenthe et al. [4] indicates that this compound cannot be the 

solubility-controlling phase (Figure 4) across the entire pCH+ range investigated. Although 

reliable data for other phases are not available, one can compare the observed with the

expected changes in U concentrations as a function of H+

 and Ca2+ concentrations (Table 3) to 

ascertain the nature of the solubility-controlling phase. First, the observed U concentrations at 

pCH+ <~7 increase by about two orders of magnitude with an order of magnitude increase in H+

concentration (one unit decrease in pCH+). This is similar to the 2.33 orders of magnitude 

increase expected in equilibrium with becquerelite, but drastically different than the expected 

increases (3 to 8 orders of magnitude per unit decrease in pCH+) in equilibrium with other Ca 

uranates (e.g., Ca2UO5(H2O)1.3-1.7, CaUO4, Ca3UO6, and CaU2O7). Second, the observed U 

concentrations at pCH+ >~7 are essentially independent of pCH+. Assuming UO2(OH)2(aq) is 

the dominant aqueous species at pCH+ >~7, the observed U concentrations are close to 0.33 

orders of magnitude increase in U per unit decrease in pCH+ as expected in equilibrium with 

becquerelite, but drastically different than expected increases (2 to 6 orders of magnitude per 

unit decrease in pCH+) in equilibrium with other Ca uranates. Third, at all pCH+ values, there is 

no clearly observable dependence on Ca2+ concentrations. This is also close to -0.17 orders of 

magnitude change with one order of magnitude increase in Ca

2+ concentrations, as expected in 

equilibrium with becquerelite, but significantly different than the expected changes (-0.5 to –

3.0 orders of magnitude) in equilibrium with other Ca uranates. Finally, the expected changes 

in U concentrations differ by many orders of magnitude (Table 3) as a function of H+

 and Ca2+

in equilibrium with becquerelite and Ca2UO5•xH2O, the only two expected solid phases [5] in 

C-12
Appendix C 

the high Ca and alkaline environments, indicating that Ca2UO5•xH2O could not possibly the 

solubility-controlling phase. Therefore, these solubility data suggest that becquerelite must be 

the solubility-controlling phase in most of the experimental range investigated. 

In summary, although we cannot rule out the formation of minor amounts of other phases in 

some of our samples, the vast preponderance of the data (i.e., XRD, total chemical 

composition, and solubility) indicates becquerelite is the solubility-controlling solid phase at 

least at pCH+ values <8. 

Thermodynamic Analysis of Data 

The solubility data at the lowest ionic strength (i.e., 0.02 M CaCl2) and in the low pH region, 

where the U(VI) hydrolysis is minimal, are best suited for determining the solubility product 

of becquerelite. As a first attempt to interpret these data, we used the standard state 

equilibrium constants for the formation of U(VI) aqueous species in the hydroxide system

proposed by Grenthe et al. [4], along with Pitzer’s [15] ion-interaction parameters for UO2

2+

with Cl-

, the bulk electrolyte used in this study. In addition, the ion-interaction parameters for 

UO2

2+ with Cl-

 were used as analogs for all of the divalent U(VI)-hydroxide species with Cl-, 

because these values are not available. With these parameters and in relatively acidic 

conditions, where the UO2

2+ species is dominant, the log of the equilibrium constant for the 

becquerelite solubility reaction 

Ca(UO2)6O4(OH)6•8H2O + 14H+

 = Ca2+ + 6UO2

2+ + 18H2O 

C-13
Appendix C 

was calculated to be 41.4±0.2. A close agreement, at all pCH+ values, between the observed 

aqueous U concentrations contacting becquerelite in 0.02 M CaCl2 solutions and those 

predicted using the above model (Figure 1) indicates that the model can be used to reliably 

predict becquerelite behavior under these conditions. 

This model was then used to predict the U(VI) concentrations in equilibrium with becquerelite 

in 0.1 M CaCl2 solutions. Model predictions showed close agreement with the observed 

concentrations in solutions of pCH+ values < 6.1 , but were up to about two orders of magnitude 

higher at the higher pCH+ values (Figure 2). The concentrations at the higher pCH+ values are 

primarily due to the dominance of UO2(OH)2(aq) in the pCH+ region 6.1 to ~9.0 and of 

UO2(OH)3

-

 at pCH+ > ~9.0. These results suggest that the formation constants of these species 

may not be correct. In the case of UO2(OH)2(aq) species, the formation constant is based on an 

upper limit for the equilibrium constant for the formation of these species (UO2

2+ + 2H2O = 

UO2(OH)2(aq) + 2H+; log K0 = ≤-10.3) reported by Grenthe et al. [4] and is very likely in error. 

In fact Silva [21], and Choppin and Mathur [22] report the log of the equilibrium constants for 

the formation of UO2(OH)2(aq) as -11.5 and -12.0, respectively. The formation constant that 

best describes our solubility data in 0.1 M CaCl2 is ~ -11.3 (because of the large variability in 

solubility data for the pCH+ where this species is dominant, an uncertainty of ±1 is associated 

with this number) and is very near the values previously proposed/used for this reaction [11, 

21]. The limiting formation constant value of UO2(OH)3

-

 (UO2

2+ + 3H2O = UO2(OH)3-

 + 3H+) 

that we calculate from our data is ≤-21.5. This species is not important in the pCH+ region <9.0 

where most of the solubility data were obtained and where becquerelite is likely to be the 

equilibrium phase. 

C-14
Appendix C 

The constants and ion-interaction parameters used in the final model are reported in Tables 4 

and 5. There is close agreement between the observed and predicted U concentrations in 

equilibrium with becquerelite in 0.02, 0.1, and 0.5 M CaCl2 solutions and as a function of pCH+ 

(Figures 1 through 3), indicating that the selected modeling parameters provide reliable 

predictions of the solubility behavior of becquerelite over a wide range of pCH+ values and Ca 

concentrations. 

It is also of interest to determine how closely this model predicts the observed solubility 

behavior of becquerelite in 1.0 M CaCl2 in the limited range of pH values reported by Sandino 

and Grambow [10]. To interpret these data, values of H+ concentrations are required. 

Although Sandino and Grambow [10] report pH values, they refer to the procedures used in 

Torrero et al. [23], which indicates that their reported pH values are really pCH+. With these 

considerations, the U concentrations observed by Sandino and Grambow [10] are compared 

with the predictions using our model (Figure 7). A very close agreement between the observed 

and predicted concentrations indicates that our model is also consistent with the data presented 

by Sandino and Grambow [10]. Our value for becquerelite solubility product is identical to the 

value calculated from the Vochten and Van Haverbeke [9] data by Casas et al. [11] (Table 4) 

using the aqueous phase model reported by Grenthe et al. [4]. However, the log of the 

solubility product value (29±1) for natural becquerelite reported by Casas et al. [11] is 

drastically different than the values (41.4 to 43.7) obtained in this study or previously reported 

for synthetic becquerelite (Table 4). In supporting their value, Casas et al. [11] state that the 

differences might be due to small particle sizes or large surface areas of synthetic samples as 

compared with the natural bacquerelite samples. Such a large variability is noted between the 

C-15
Appendix C 

amorphous and crystalline tetravalent oxides. However, such variability is not expected for 

solid phases that tend to initially precipitate as crystalline solids as is the case with 

becquerelite. Casas et al. [11] calculate their solubility product based on only one sample that 

was adjusted to four different pH values at different times. Two of their data points are for pH 

values 7.4 and 8.4 where the aqueous phase model is not reliable and our study indicates 

difficulty in maintaining becquerelite under highly alkaline conditions. Although, Casas et al.

[11] took precautions to exclude impurities from the becquerelite samples, their equilibrated 

sample contained evidence of the presence of <5% soddyite and uranophane. The presence of 

small percentages of impurities that are difficult to exclude and identify in natural samples can 

have a significant effect on solubility. In addition, they did not investigate solubility as a 

function of Ca, which is necessary to 1) obtain reliable data because Ca is one of the solid 

phase components and 2) convert schoepite-type phases, which may be present as impurities 

and have been shown to transform to becquerelite at room temperature in the presence of Ca, 

so that reliable thermodynamic constants for becquerelite can be determined. We can only 

point out the difficulties in the study, but the specific reasons for the drastically different 

solubility product observed by Casas et al. [11] are not known. Further insights into this 

problem can only be gained through extensive studies, hitherto lacking, with the natural 

becquerelites. 

In summary, the solubility product of synthetic becquerelite was determined through extensive 

studies on solubility as a function of wide ranges in pCH+ and Ca concentrations. The observed 

solubilities were similar to those previously reported for synthetic becquerelites (Table 4). An 

unexpected reported differences of over 12 orders of magnitude [11] between the solubility 

C-16
Appendix C 

products of natural and synthetic becquerelites can only be resolved through additional 

extensive studies with natural becquerelites. 

Acknowledgements 

This research was conducted at the Pacific Northwest National Laboratory, operated by 

Battelle for the U. S. Department of Energy (DOE) under contract DE-AC06-76RL0 1830. 

The research was funded by the U. S. Nuclear Regulatory Commission under project W6409. 

We thank Dr. Phillip R. Reed of the U. S. Nuclear Regulatory Commission for programmatic 

support and technical discussions. We thank Ms. Debra M. Hinton for text processing of this 

document (Becquerelite 20reportA081401.doc). 

C-17
Appendix C 

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Wanner, H.: Chemical Thermodynamics of Uranium, North-Holland, Elsevier Science 

Publishers, Amsterdam, The Netherlands (1992). 

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Environment and its Specific Interactions with Uranium and Iodine. Radiochim. Acta 

44/45, 225-261 (1988). 

6 Deliens, M., Piret, P., Comblain, G.: In: Les minéraux secondaires d’uranium du Zaire, 

Musee Royal de l’Afrique centrale, Tervuren, Belgique, D/1981/0254/7 (1981). (quoted by 

Sandino and Grambow 1994). 

C-18
Appendix C 

7 Bates, J. K., Tani, B. S., Veleckis, E., Wronkiewicz D. J.: Identification of Secondary 

Phases Formed During Unsaturated Reaction of UO2 with EJ-13 Water. Mat. Res. Soc. 

Symp. Proc. 176, 499-506 (1990). 

8a Wronkiewicz, D. J., Bates, J. K., Gerding, T. J., Veleckis, E., Tani, B. S.: Uranium Release 

and Secondary Phase Formation During Unsaturated Testing of UO2 at 90°C. J. Nuc. Mat. 

190, 107-127 (1992). 

8b Wronkiewicz, D.J. and Buck, E.C.: Uranium Mineralogy and the Geologic Disposal of 

Spent Nuclear Fuel. In, URANIUM: Mineralogy, Geochemistry and the Environment, 

Reviews in Mineralogy, Volume 38, 475-497 (1999), P.C. Burns and R. Finch, eds. The 

MINERALOGICAL SOCIETY OF AMERICA, Washington, DC 20036. 

9 Vochten, R., Van Haverbeke, l.: Transformation of Schoepite into the Uranyl Oxide 

Hydrates: Becquerelite, Billietite and Wolsendorfite. Mineralogy and Petrology 43, 65-72 

(1990). 

10 Sandino, M. C. A., Grambow, B.: Solubility Equilibria in the U(VI)-Ca-K-Cl-H2O System: 

Transformation of Schoepite into Becquerelite and Compreignacite. Radiochim. Acta 

66/67, 37-43 (1994). 

11 Casas, I., Bruno, J., Cera, E., Finch, R. J., Ewing, R. C.: Characterization and Dissolution 

Behavior of a Becquerelite from Shinkolobwe, Zaire. Geochimica et Cosmochim. Acta 

C-19
Appendix C 

61/18, 3879-3884 (1997). 

12 Rai, D., Felmy, A. R., Juracich, S. P., Rao, L.: Estimating the Hydrogen Ion Concentration 

in Concentrated NaCl and Na2SO4 Electrolytes. SAND94-1949, Sandia National 

Laboratories, Albuquerque, New Mexico (1995). 

13 Rai, D., Hess, N. J., Felmy, A. R., Moore, D. A., Yui, M., Vitorge, P.: A Thermodynamic 

Model for the Solubility of PuO2(am) in the Aqueous K+

-HCO3

-

 -CO3

2- -OH-

 -H2O System. 

Radiochim. Acta 86, 89-99 (1999). 

14 Pitzer, K. S.: Mayorga, G.: Thermodynamics of Electrolytes. II. Activity and Osmotic 

Coefficients for Strong Electrolytes with One or Both Ions Univalent. J. Phys. Chem. 77, 

2300-2308 (1973). 

15 Pitzer, K. S.: “Ion Interaction Approach: Theory and Data Correlation.” Chapter 3, pp. 

75-153, Activity Coefficients in Electrolyte Solutions. K. S. Pitzer, ed.; CRC Press, Boca 

Ratan, Florida (1991). 

16 Felmy, A. R., Weare, J. H.: The Prediction of Borate Mineral Equilibria in Natural Waters: 

Application to Searles Lake, California. Geochim. Cosmochim. Acta 50, 2771-1783 

(1986). 

17 Felmy, A. R., Rai, D., Schramke, J. A., Ryan, J. L.: The Solubility of Plutonium

C-20
Appendix C 

Hydroxide in Dilute Solution and in High-Ionic-Strength Chloride Brines. Radiochim. 

Acta 48, 29-35 (1989). 

18 Felmy, A. R., and D. Rai.: An Aqueous Thermodynamic Model for a High-Valence 4:2 

Electrolyte Th4+-SO4

2- in the System Na+

-K+-Li+-NH4

+

-Th4+-SO4

2--HSO4-

-H2O to High 

Concentration. J. Solution Chem. 21, 407-423 (1992). 

19 Rai, D., Felmy, A. R., Moore, D. A.: Thermodynamic Model for Aqueous Cd2+-CO3

2- Ionic 

Interactions in High-Ionic-Strength Carbonate Solutions, and the Solubility Product of 

Crystalline CdCO3. J. Solution Chem. 20, 1169-1187 (1991). 

20 Rai, D., Felmy, A. R., Fulton, R. W.: The Nd3+ and Am3+ Ion Interactions With Sulfate Ion 

and Their Influence on NdPO4(c) Solubility. J. Solution Chem. 24, 79-895 (1995). 

21 Silva, R. J.: Mechanisms for the Retardation of Uranium (VI) Migration. Mat. Res. Soc. 

Symp. Proc. 257, 323-330 (1992). 

22 Choppin, G. R., Mathur, J. N.: Hydrolysis of Actinyl (VI) Cations. Radiochim. Acta 52/53,

25-28 (1992). 

23 Torrero, M. E., Casas, I., De Pablo, J., Sandino, M. C. A., Grambow, B.: A Comparison 

Between Unirradiated UO2(s) and Schoepite Solubilities in 1 M NaCl Medium. 

Radiochim. Acta 66/67: 29-35 (1994). 

C-21
Appendix C 

24 Harvie, C. E., Moller, N., Weare, J. H.: The Prediction of Mineral Solubilities in Natural 

Waters: The Na-K-Mg-Ca-H-CL-SO4-OH-HCO3-CO2-H2O System to High Ionic 

Strengths at 25°C. Geochim. Cosmochim. Acta 48, 723-751 (1984). 

C-22
Appendix C 

Figure Captions 

Figure 1. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.02 M CaCl2 and a range in pCH+ values that were equilibrated for different periods. 

Solid line represents model predictions based on the thermodynamic data reported in 

Tables 4 and 5. 

Figure 2. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.1 M CaCl2 and a range in pCH+ values that were equilibrated for different periods. 

The presence of becquerelite at pCH+ > 8 is uncertain, see text for details. The lines 

represent predictions based on thermodynamic data reported in Tables 4 and 5 with 

the exception that the dashed line incorporates values of formation constants for 

UO2(OH)2

0

 and UO2(OH)3

-

 from Grenthe et al. [4]. 

Figure 3. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.5 M CaCl2 and a range in pCH+ values that were equilibrated for different periods. 

Solid line represents model predictions based on thermodynamic data reported in 

Tables 4 and 5.

C-23
Appendix C 

Figure 4. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.02, 0.1, or 0.5 M CaCl2 and a range in pCH+ values. Solid line represents a 

reference slope of -2. Dashed line represents predicted uranium concentrations in 

equilibrium with CaUO4(c) at 0.1 M CaCl2 based on thermodynamic data reported in 

Grenthe et al. [4]. 

Figure 5. A representative X-ray diffraction pattern of the solid phase equilibrated in 0.1 M 

CaCl2 at pCH+ of about 8. See Table 1 for details about XRD analyses of samples at 

other pCH+ values. 

Figure 6. Comparison of the Fourier transforms of the EXAFS spectra of solids equilibrated in 

different molarities of CaCl2 solutions (U65, 0.02 M CaCl2, pCH+ 5.9; Ul08, 0.1 M 

CaCl2, pCH+ 7.6; U209, 0.5 M CaCl2, pCH+ 6.2). The thin lines are the Fourier 

transforms of the experimental EXAFS; the thick lines are the Fourier transforms of

the fit to EXAFS. Transforms were calculated over the range from 3.5 to 12.5 ∆-1 and 

are offset by 0.15 units for ease of comparison. 

Figure 7. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

1.0 M CaCl2. The symbols representing experimental data points are from Sandino 

and Grambow [10] (labeled as S&G 1994). The solid line represents model 

predictions based on thermodynamic data reported in Tables 4 and 5. 

C-24
Appendix C 

Figure 1. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.02 M CaCl2 and a range in pCH+ values that were equilibrated for different periods. 

Solid line represents model predictions based on the thermodynamic data reported in 

Tables 4 and 5. 

C-25
Appendix C 

Figure 2. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.1 M CaCl2 and a range in pCH+ values that were equilibrated for different periods. 

The presence of becquerelite at pCH+ > 8 is uncertain, see text for details. The lines 

represent predictions based on thermodynamic data reported in Tables 4 and 5 with 

the exception that the dashed line incorporates values of formation constants for 

UO2(OH)2

0

 and UO2(OH)3

-

 from Grenthe et al. [4]. 

C-26
Appendix C 

Figure 3. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.5 M CaCl2 and a range in pCH+ values that were equilibrated for different periods. 

Solid line represents model predictions based on thermodynamic data reported in 

Tables 4 and 5. 

C-27
Appendix C 

Figure 4. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

0.02, 0.1, or 0.5 M CaCl2 and a range in pCH+ values. Solid line represents a 

reference slope of –2. Dashed line represents predicted uranium concentrations in 

equilibrium with CaUO4(c) at 0.1 M CaCl2 based on thermodynamic data reported in 

Grenthe et al. [4]. 

C-28
Appendix C 

Figure 5. A representative X-ray diffraction pattern of the solid phase equilibrated in 0.1 M 

CaCl2 at pCH+ of about 8. See Table 1 for details about XRD analyses of samples at 

other pCH+ values. 

C-29
Appendix C 

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 678 9 10

Radial distance (A)

Fourier transform amplitude

data fit

U209

U108

U65

Figure 6. Comparison of the Fourier transforms of the EXAFS spectra of solids equilibrated in 

different molarities of CaCl2 solutions (U65, 0.02 M CaCl2, pCH+ 5.9; Ul08, 0.1 M 

CaCl2, pCH+ 7.6; U209, 0.5 M CaCl2, pCH+ 6.2). The thin lines are the Fourier 

transforms of the experimental EXAFS; the thick lines are the Fourier transforms of

the fit to EXAFS. Transforms were calculated over the range from 3.5 to 12.5 ∆-1 and 

are offset by 0.15 units for ease of comparison. 

C-30
Appendix C 

Figure 7. Aqueous uranium concentrations in solutions contacting becquerelite suspensions in 

1.0 M CaCl2. The symbols representing experimental data points are from Sandino 

and Grambow [10] (labeled as S&G 1994). The solid line represents model 

predictions based on thermodynamic data reported in Tables 4 and 5. 

C-31
Appendix C 

Table 1. X-ray diffraction analyses of solid samples contacting 0.1 M CaCl2

pCH+ Major Phase 

4.3 Becquerelite a,b

6.3 Becquerelite a

8.0 Becquerelite a

11.0 Inconclusive c

a Becquerelite (Ca (UO2)6O4(OH)6•8H2O) was found to be the major phase in 

the samples. There were some low-intensity, unaccounted peaks 

corresponding to unknown minor phase. 

b The major phase in this sample was highly preferentially oriented along (00L). 

c The experimental pattern was vaguely similar to reference powder data for 

bacquerelite, but the quality of the match was not conclusive.

C-32
Appendix C 

Table 2. Molar U to calcium ratios in washed solids 

that were equilibrated in different CaCl2

solutions

CU/mol dm-3

CCaCl2/mol dm-3

pCH+

CCa/mol dm-3

0.1 4.30 5.6

0.1 7.99 5.4

0.1 8.84 3.7

0.1 11.00 1.6

0.02 11.36 2.2

0.5 11.42 2.1

C-33
Appendix C 

Table 3. Expected changes in uranium concentrations with the changes in H+

 and Ca2+

concentration in equilibrium with different Ca-U(VI) solids.

Changes in log (CU/mol dm-3) 

with one log unit increase in Reaction 

CH+/mol dm-3 CCa

2+/mol dm-3

Reactions Involving UO2

2+

Ca(UO2)6O4(OH)6Χ8H2O + 14H+ ≡ Ca2+ + 6UO2

2+ + 18H2O 2.33 -0.17

Ca2UO5ΧxH2O + 6H+ ≡ 2Ca2+ + UO2

2+ + (x + 3) H2O 6.0 -2.0

CaUO4(c) + 4H+ ≡ Ca2+ + UO2

2+ + 2H2O 4.0 -1.0

Ca3UO6 + 8H+ ≡ 3Ca2+ + UO2

2+ + 4H2O 8.0 -3.0

CaU2O7 + 6H+ ≡ Ca2+ + 2UO2

2+ + 3H2O 3.0 -0.5

Reactions Involving UO2(OH)2

0

Ca(UO2)6O4(OH)6Χ8H2O + 2H+ ≡ Ca2+ + 6UO2(OH)2

0

 + 6 H2O 0.33 -0.17

Ca2UO5ΧxH2O + 4H+ ≡ 2Ca2+ + UO2(OH) 2

0

 + (x + 1) H2O 4.0 -2.0

CaUO4(c) + 2H+ ≡ Ca2+ + UO2(OH) 2

0 2.0 -1.0

Ca3UO6 + 6H+ ≡ 3Ca2+ + UO2(OH) 2

0

 + 2H2O 6.0 -3.0

CaU2O7 + 2H+ ≡ Ca2+ + 2UO2(OH) 2

0

 1.0 -0.5

C-34
Appendix C 

Table 4. Thermodynamic data for reactions involving uranium species used in this study.

Reaction log K0 Reference

UO2

2+ + H2O ≡ UO2OH+

+ H+ -5.2 [4]

UO2

2++ 2H2O ≡ UO2(OH)20 + 2H+ ~ -11.3a This study

UO2

2+ + 3H2O ≡ UO2(OH)3- + 3H+ ≤ -21.5a This study

UO2

2+ + 4H2O ≡ UO2(OH)42- + 4H+ -33.0 [4]

2UO2

2+ + 2H2O ≡ (UO2)2(OH)22+ + 2H+ -5.62 [4]

3UO2

2+ + 4H2O ≡ (UO2)3(OH)42+ + 4H+ -11.9 [4]

3UO2

2+ + 5H2O ≡ (UO2)3(OH)5+ + 5H+ -15.55 [4]

3UO2

2+ + 7H2O ≡ (UO2)3(OH)7

- 

+ 7H+ -31.0 [4]

Ca(UO2)6O4(OH)6•8H2O(c) + 14H+ ≡ Ca2+ + 6UO2

2+ + 18H2O 41.4±0.2b This study

41.89±0.5c [10]

43.7±0.47c [10]

43.6±0.3c [9]

41.4 c,d Calculated

29±1c [11]

a The value quoted by Grenthe et al. [4] for the formation of UO2(OH) 0

2 and UO2(OH)3

-

 are 

<–10.3 and –19.2±0.4, respectively. 

b This value was calculated based on the data at relatively low pCH+ values and is not 

significantly impacted by the choice of constants for the formation of UO2(OH) 0

2 and 

UO2(OH)3

-

, because these species are not dominant in the low pCH+ region. 

c The values are based on a few experiments conducted in a very narrow range of pH values 

and Ca concentrations. See text for details. 

d Value calculated by Casas et al. [11] from the data reported by Vochten and Van Haverbeke 

[9] and using the aqueous thermodynamic model of Grenthe et al. [4].

C-35
Appendix C 

Table 5. Pitzer ion-interaction parameters used in this study.

Binary Parameters 

Species β(0) β(1) β(2) Cφ source 

H+, Cl- 0.1775 0.2945 0.0 0.00080 [24]

Ca2+, Cl- 0.3159 1.6140 0.0 -0.00034 [24]

UO2

2+, Cl- 0.4270 1.6440 0.0 -0.03690 [15]

(UO2)2(OH)2

2+, Cl- 0.4270 1.6440 0.0 -0.03690 This study a

(UO2)3(OH)2

2+, Cl- 0.4270 1.6440 0.0 -0.03690 This study a

Common-Ion Ternary Parameters (all values from Harvie et al. [24]) 

H+, Ca2+ 0.092

H+, Ca2+, Cl- -0.015

Cl

-

, OH- -0.050

Ca

2+,Cl-

, OH- -0.025

a Assumed to be identical to UO22+, Cl- parameters reported by Pitzer [15].

C-36
Appendix C 

Appendix 

Complete sets of becquerelite solubility in different solutions presented in Figures 1 

through 4 are reported in the following tables (Tables A.1, A.2, and A.3). 

C-37
Appendix C 

Table A.1 Solubility of becquerelite in 0.02 M CaCl2 solutions at different 

equilibration periods.

4 days 9 days 32 days 

pCH+a log CU/mol dm-3pCH+a log CU/mol dm-3pCH+a log CU/mol dm-3

4.579 -3.052 4.623 -2.996 4.582 -2.863

4.869 -3.336 4.892 -3.338 5.386 -4.120

5.087 -3.577 5.084 -3.510 6.164 -5.469

5.353 -4.008 5.306 -3.893 11.359 -6.405 

5.651 -4.492 5.367 -4.054

5.730 -4.666 5.586 -4.362

5.965 -5.161 5.638 -4.483

6.153 -5.283 5.861 -4.812

6.463 -5.754 5.964 -4.928

6.660 -6.073 6.250 -5.462

6.922 -6.463 6.426 -5.678

11.561 -6.642 6.617 -5.959

11.482 -6.857

a pCH+ = pH(obs) + 0.134 

 

C-38
Appendix C 

Table A.2 Solubility of becquerelite in 0.01 M CaCl2 solutions at different 

equilibration periods. 

7 days 24 days 70 days 

pCH+a log CU/mol dm-3pCH+a log CU/mol dm-3pCH+a log CU/mol dm-3

4.497 -2.189 4.470 -2.218 4.296 -2.700

4.620 -2.355 4.619 -2.348 7.986 -6.560

4.896 -2.785 4.799 -3.030 8.838 -7.010

5.207 -3.301 4.821 -2.654 10.998 -6.750

5.629 -4.128 4.839 -3.034

5.758 -4.277 4.889 -3.032

6.180 -5.015 4.924 -3.217

6.479 -5.664 5.161 -3.260

6.499 -5.510 5.943 -4.664

6.636 -5.772 6.113 -4.975

6.770 -5.839 6.372 -5.442

6.965 -6.206 6.588 -5.866

7.860 -6.670 7.479 -6.845

8.257 -7.263 7.613 -7.055

8.284 -6.644 7.638 -6.996

8.413 -7.146 7.708 -6.613

8.603 -7.377 8.096 -6.810

8.921 -6.963 8.186 -7.201

9.442 -7.146 8.458 -7.055

9.601 -7.201 9.128 -6.764

9.839 -7.121 9.234 -6.873

10.087 -7.900 9.287 -7.423

10.442 -7.532 10.070 -7.474

11.355 -7.173

a pCH+ = pH(obs) + 0.161 

C-39
Appendix C 

Table A.3 Solubility of becquerelite in 0.5 M CaCl2

solutions at different equilibration periods. 

4 days 18 days 

pCH+a log CU/mol dm-3pCH+ a log CU/mol dm-3

4.738 -2.701 4.762 -2.676 

5.039 -3.243 5.026 -3.218 

5.236 -3.724 5.259 -3.570 

6.079 -5.265 5.445 -4.007 

6.150 -5.481 5.649 -4.395

6.260 -5.593 5.698 -4.474

6.550 -6.031 5.879 -4.879 

11.433 -6.449 6.011 -5.032 

6.225 -5.350

6.229 -5.452

6.599 -6.007

11.422 -6.719

a pCH+ = pH(obs) + 0.283 

C-40