Separations for the Nuclear Fuel Cycle in the 21st Century - American

Chapter 20

Downloaded by UNIV MASSACHUSETTS AMHERST on August 9, 2012 | http://pubs.acs.org Publication Date: June 9, 2006 | doi: 10.1021/bk-2006-0933.ch020

Speciation and Solubility Modeling of Actinides in the Waste Isolation Pilot Plant Donald E. Wall, Nathalie A. Wall, and Laurence H. Brush Carlsbad Programs Group, Sandia National Laboratories, Carlsbad, N M 88220

The WIPP geochemical model uses the Pitzer equations coupled to a thermodynamic database to carry out speciation and solubility calculations for the actinides in the +III, +IV, and +V oxidation states in aqueous systems composed of N a K -Mg -Ca -SO -OH -CO -HCO -H O-acetate-citrate-oxalate-EDTA. The WIPP database incorporates results for actinide speciation and complexation work carried out primarily at Pacific Northwest National Laboratory, Forschungszentrum Karlsruhe (Germany) and Florida State University. Calculations are performed at Sandia National Laboratories with the code F M T , using the Harvie-MøllerWeare database, and parameters that were developed specifically for actinides in high ionic strength aqueous solutions. This paper describes derivation of the thermodynamic database, and provides normalized standard chemical potentials and Pitzer parameters for modeling An(III, IV, and V ) speciation and solubility in brines. +

+

2 +

2 +

2 -

4

-

2-

3

-

3

2

© 2006 American Chemical Society

In Separations for the Nuclear Fuel Cycle in the 21st Century; Lumetta, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

313

314

Introduction The Waste Isolation Pilot Plant, located 42 km east of Carlsbad, New Mexico has been accepting defense related transuranic waste since March 1999. The repository is located approximately 655 meters below the surface in the Salado Formation, a bedded salt formation. The salt formation is primarily halite (NaCl), but also contains clay seams, anhydrite (CaS0 ), gypsum (CaS0 *2H 0), polyhalite ( K M g C a ( S 0 V 2 H 0 ) and magnesite ( M g C 0 ) . In the undisturbed state, reconsolidation of the host rock will establish a postclosure environment that will prevent the movement of radionuclides due to the low porosity and permeability of the halite of the Salado Formation. Brine from the Salado enters the repository through dewatering of the disturbed rock zone whereas brine may also enter from the Castile Formation i f exploratory drilling for natural resources intersects a disposal area and an underlying brine pocket. Radionuclides may, under certain conditions, move to the accessible environment as dissolved, suspended, or colloidal material, with the magnitude of a direct brine release (DBR) proportional to the radionuclide solubility. Brine solution chemistry will be controlled by emplacement of MgO, which will buffer the brines at mildly basic pH about 9 and act as a sink for C 0 " that could form as a result of C 0 production by microbes that act upon the cellulosic, plastic, and rubber materials in the waste. 4


4

2

2

2

4

2

3

2

3

2

239>240

2 4 l

The radionuclides of greatest concern in the WIPP are P u and A m , which account for more than 99% of the total radioactivity for most of the 10,000 year regulatory period. Iron will be emplaced within the repository as part of the waste and waste drums, and will maintain a chemically reducing condition. As a result, Pu is expected to exist as Pu(III) or Pu(IV) and A m as Am(III). U is modeled as U(IV) in half of the performance assessment vectors and as U(VI) in the other half; likewise, Np is modeled as Np(IV) in half of the vectors and as Np(V) in the other half. Speciation and solubility calculations are carried out for three oxidation states, An(III, IV, and V ) but not for An(VI) due to the propensity of U(VI) to form polynuclear species, for which the thermodynamic database for modeling at high ionic strengths is inadequate. The solubility values for U(VI) have been determined based upon a literature survey of the most relevant solubility studies (/). +

+

+

2 +

2+

Ions of importance in Salado and Castile brines are H , N a , K , M g , C a , OH", CI", C 0 " , and S0 ". Representative compositions of the Salado and Castile brines are given in Table I (2,3). Actinide solubilities may also be influenced by the predominant organic ligands present in the waste: acetate, citrate, oxalate, and E D T A . The semi-empirical Pitzer equations are used to calculate the ionic activity coefficients for the actinides, and inorganic and organic complexing agents in the WIPP inventory. Solubilities are calculated with the Fracture Matrix Transport (FMT) code, which determines the minimum Gibbs free 2

3

2

4


315 Table I. Composition of the W I P P Brines Component B(III)° Br" Ca CI' K Mg Na SQ " 2+

+

2 +


+

2

4

b

Castile Fm. (mM) 63 11 12 4800 97 19 4870 170

c

Salado Fm.(mM) 156 27 14 5610 467 1020 3570 178

#

B is added to the synthetic brines as N a B O 1 0 H O Described by Popielak et al. (5) Described by Snider (2) 2

4

7

2

energy for an input array of possible system components. The speciation and solubility of each oxidation state are determined separately, without accounting for redox interchanges among the available oxidation states. The Pitzer parameters that describe the ionic activity coefficients were either taken directly from the literature or calculated with the code N O N L I N , which was developed by A . Felmy at P N N L . The N O N L I N calculations were applied to results of studies of the variation of stability constants of actinides with organic ligands as functions of ionic strength. Much of the F M T database, including standard chemical potentials and Pitzer parameters, was developed during the 1990's to carry out speciation and solubility calculations for actinides in high NaCl content brines. Most of the early work focused on the influence of inorganic ligands, such as C 0 " , OH", and S0 ", with additional focus on organic ligands as more data became available on the composition of the wastes destined for the WIPP. Compilation of the database is described in a series of S N L memoranda written by C.F. Novak and E.R. Giambalvo; the memoranda are available from the WIPP records center (4-10). This paper lists the normalized standard chemical potentials (j!°/RT) and the Pitzer parameters for the species used in speciation and solubility calculations for the WIPP. The \x°/RT values for the WIPP modeling were based upon a review of relevant literature reports, and research programs funded by the WIPP project. Some values from the N E A database were incorporated in the WIPP calculations, and are also included in the present data tables (//). The symbols used to denote binary Pitzer parameters are very similar to those commonly used to represent stability constants. The binary Pitzer parameters are indicated by (J , p , (J and C ° with superscript numerals in parentheses for the P terms. Stability constants that use the P symbol may include a superscript zero without parentheses when standard state conditions 2

3

2

4

(0)

(1)

(2)


316 are indicated, and may include a subscript index of the form p ; the indices p,q,r respectively indicate the number of metal ions, protons, and ligands involved in complex formation. The subscript index is omitted i f the context is clear. The p terms for Pitzer parameters always use superscript numbers in parentheses, the p terms for stability constants never use the parentheses either in superscript or subscript.


pqr

The An(III) Model Most of the work on An(III) complexation has been performed with Am(III) or Cm(III). These data have been used to generate a model for An(III) speciation and solubility. Due to the similarity of the chemical behavior of Pu(III), Am(III), and Cm(III), the chemical potentials, stability constants, and Pitzer parameters that were determined for Am(III) and Cm(III) have been applied to modeling of the Pu(III) solution behavior. The reactions with inorganic species that are used to model the speciation and solubility for Am(III) and Pu(III) are given below.

2

+ 2C0 3

An

3 +

An

3 +

2

+ 3C0 2

3 +

3 +

An

An

+

3 +

~ AnOH

3 +

3 +

2 +

3 +

+ 2

* An(OH) (aq) 3

+ 30H"

An

An

5

4

+ 20H" ~ An(OH)

An

An

3

3

+ OH"

3 +

2

~ An(C0 ) "

+ 30rT

3 +

3

3

+ 4C0 " 3 +

-' A n ( C 0 ) 3

3

An

3

- An(C0 ) -

3

An

An

2

3

3 +

An

+

+ C 0 - ^* A n C 0

3 +

An

An(OH) (s) 3

+ Cr

~ AnCl

+ 2Cr 2

+ S0 4

2 +

-• A n C I

+ 2

* An(S0 )

+

4

2

+ 2S0 ' ~ An(S0 ) ' 4

4

2

2

+ OH" + C 0 " '* A n C 0 O H ( s ) 3

3 +

3

2

N a + A n + 2 C 0 " + 6 H 0 •» N a A n ( C 0 ) « 6 H 0 ( s ) 3

An

3 +

2

3

+ P0 ' 4

3

2

2

AnP0 (cr) 4

FanghSnel et al. {12) used peak deconvolution of time resolved laser fluorescence spectra (TRLFS) to measure the stability constants of formation of the carbonate complexes Cm(C0 ) " " in 0-6 m NaCl solution at 25 °C. The 3

3

2

n


317 Table II. Normalized Standard Chemical Potentials for An(III) Species An AnC0 An(C0 ) An(C0 ) An(C0 ) " AnS0 An(S0 ) ' AnOH An(OH) An(OH) (aq) AnCl AnCl AnC0 OH(cr) AnCO OH«0.5H O(cr) AnC0 OH(am,hyd) An(OH) (s) NaAn(C0 ) «6H 0 AnP0 (cr)

fi"/Rr -241.511 ± 1.918 -472.882 ± 2 . 1 3 4 -697.116 ± 2 . 3 8 4 -914.903 ±3.034 Not available -549.235 ± 1.956 -850.282 ± 1.978 -320.593 ±2.237 -398.063 ± 2.505 -468.165 ± 2 . 2 3 8 -294.995 ± 1.920 -345.671 ± 1.924 Not available -617.291 ± 5.560 -564.396 -492.572 ± 2.364 Not available Not available

AnP0 (am, hyd)

-712.268 ± 1.382

i+

+

3

3

2

3

3

3

5

3

4

+

4


4

2

2 +

+

2

3

2 +

+

2

3

3

2

3

3

3

2

2

4

4

a

-241.694 -473.29 ± 0 . 6 9 -697.52 ± 1.38 -915.53 ± 0 . 9 2 - U 2 3 . 4 0 ± 1.15 -549.56 -850.99 -319.96 ± 0 . 2 1 -396.89 ± 0.46 -469.53 -295.20 ± 0 . 0 7 -345.90 ± 0 . 1 2 -570.34 c

c

Ref. 32 12 12 12 12 16 16 17 17 19,34 19 19 12, 13

19,33 35 21

-495.32 -1396.468 -709.75

N E A database values; uncertainties are the 95% confidence limit (7/)

b

WIPP values based on referenced work, derivation of the uncertainties are

not

described in some of the references c

based on non-published work that was cited in the reference

standard chemical potentials for the carbonate complexes are listed in Table II; the Pitzer parameters are given in Tables III through V . Fanghanel et al. (12) reported standard state complexation constants for C m ( C 0 ) " at zero ionic strength of log p°,oi = 8.1 ± 0.3, log p ° = 13.0 ± 0.6, log p ° = 15.2 ± 0.4, log P° 4 = 13.0 ± 0.5; a description of the derivation of error limits was not provided. The authors also noted that there was no indication of formation of mixed hydroxide-carbonate complexes. Finally, the authors compared published solubility data to model predictions using their stability constant values, Pitzer parameters, and a log K° = -22.7 for AmC0 OH(s). The fit of the model to the experimental data of Felmy et al. (13), Bernhopf (14) and Giffaut (15) was good, especially in the log [C0 "] range of 10" to 10" M , which is particularly relevant for WIPP conditions. Fanghanel and K i m (16) published a review of Cm(III) complexation with CI', S0 ", C 0 " and OH". The authors describe examination of the fluorescence of Cm(III) with various S 0 " concentrations, and plot the variation 3

3

102

2n

n

103

10

sp

3

2

6

7

3

2

4

2

3

2

4


318 Table III. Binary Pitzer Parameters for An(III) Cation Na Na Na AnC0 An AnS0 Na An An An AnOH An(OH) AnCl AnCl

-0.24 0.125 2.022 -0.072 1.792 -0.091 -0.354 0 0.8 0.5856 -0.055 -0.616 0.593 0.516

2

3

+

3

+

3

3

3

4

5

+

cr so cr

3

2

3+

4

+

4

+


f

Anion An(C0 ) " An(C0 ) An(C0 ) "

+

2

An(S0 ) H P0 4

3+

2

2

4

cio cr cr cr cr cr

3+

4

3+

2+

+ 2

2+

+

2

0.224 4.73 19.22 0.403 15.04 -0.39 0.4 0 5.35 5.60 1.60 -0.45 3.15 1.75

0 0 0 0 0 0 0 -93 0 0 0 0 0 0

C*

Ref

0.0284 0.0007 -0.305 0.0388 0.600 0.048 0.051 0 -0.0048 -0.016 0.050 0.050 -0.006 0.010

12 12 12 12 16 16 16 36 13 19 19 19 19 19

Table IV. Neutral Ion Interaction Parameters for An(III) Species An(OH) (aq) An(OH) (aq) 3

Ion Na

3

cr

X -0.2 -0.2

+

Ref. 19 19

Table V . Ternary Interaction Parameters (0,i|/) for An(III) Ion i Ca Ca Ca Na

Ionj An AnCl AnCl An An(C0 ) -

5 +

3 +

2 +

2 +

2+

+

2

+

3 +

cr so '

3

3

2

9

^

Ref

cr cr cr cr

0.2 -0.014 -0.196 0.1 0 0

0 0 0 0 0 0

19 19 19 19 12 36

Na Na

3

CIO4"

4

Ion k

+

+

U

in the log p | i and log p values as a function of NaCl concentration over a range of 0 to 6 m. The authors state that the data were used to develop parameters for the SIT model. The An(III)-S0 ' stability constant and Pitzer parameters used in WIPP modeling are based on work with Cm(III), presented in Table 1 of a report by Fanghanel and Kim (16), which references unpublished data from their laboratory as the source of the parameter values. As of the date of this writing, detailed results of the study describing the measurement of the Cm(III)-S0 " stability constants and Pitzer parameter data have not been published. As a result, we have not attempted to evaluate the uncertainty associated with the An(III)-S0 " parameters. 0

102

2

4

2

4

2

4


319 Pitzer parameters and stability constants of formation for the An(III) hydroxides were reported by Fanghanel et al. (17). The stability constants were determined in 1,2, and 4 m NaCl solutions by examination of the Cm spectra using T R L F S . Varying the pH from 4 to 10, the investigators report the existence of three Cm species: C m , Cm(OH) , and Cm(OH) . The authors used the data to determine the binary Pitzer parameters P(0), P (1) and C ° for the Cm(III) hydrolysis species, and using the Pitzer equations, they extrapolated the stability constants to zero ionic strength, and determined log P°i i 6.44 ± 0.09 and log p°io2 = 12.3 ± 0.2; a description of the derivation of error limits was not provided. As a test of the suitability of the parameters, the authors compared the predicted values with experimental solubilities of Am(OH) in 5.61 m NaCl solution over a pH range of 5 to 12, and found good agreement. Additionally, the authors note that the thermodynamic model predicts a solubility for Am(OH) at pH = 9 to be about four orders of magnitude greater in saturated NaCl solution than in deionized water. The reported stability constants were used to calculate the standard chemical potentials of formation of the hydroxide complexes. Fanghanel et al. (18) reported results of a study of inner sphere CI" complexation of Cm(III) in a p H = 2 solution, varying the CI' concentration from 2 < [CaCl ] < 6.5 m by addition of C a C l . The authors reported difficulty extrapolating to zero ionic strength due to a lack of data at lower CI" concentrations, although a further analysis reported later by the same research group (19) provides the Pitzer parameters and values of log P°ioi 0.24 ± 0.03 and P°io2 -0.74 ± 0.05, for 25 °C and zero ionic strength; a description of the derivation of error limits was not provided. Harvie et al. (20) stated that the behavior of complexes of the metal ion of interest with the anion in the bulk electrolyte is sufficiently described in the P(0), p , and C ° parameters as ionic strength effects when complexation constants are less than log p = 1.3 in dilute solution. Complexation by CI" of An(III) has much less effect on the solubility under WIPP conditions than the ionic strength effect exerted by the presence of large amounts of CI". 3+

2+

+

2

=


0

3

3

2

2

=

=

(l)

3

The anions P 0 " and C10 " are not important components in the WIPP inventory, but were included in the database to accommodate possible future changes. Neither component is currently included in the WIPP geochemical model. The N E A database (77) provides a chemical potential for AmP0 (am,hyd), while a similar value is quoted by Rai et al. (21) for a crystalline phase. Both values are reproduced in Table II. The solubilitylimiting solid phase that is used in WIPP speciation and solubility calculations for trivalent actinides is Am(OH) with a log K ° = -27.5 at 25 °C and zero ionic strength. Consequently, Am(OH) is less soluble under WIPP conditions (pH s 9 and [C0 "] s 10" m) than AmC0 OH(cr), as described by Fanghanel et al. (72), based on work of Felmy et al. (75). The log K° and standard 4

4

4

3

sp

3

2

3

5

3

sp


320 chemical potential values for AmC0 OH(cr) are -22.7 and -570.34, respectively. The N E A database (//) does not provide data for AmC0 OH(cr), but includes values for AmCO OH«0.5H O(cr) and AmC0 OH(am,hyd). 3

3

3

2

3


The An(IV) Model The actinides that can exist in the +IV oxidation state that are also in the WIPP inventory include Th(IV), U(IV), Np(IV) and Pu(IV). Much of the data used as input into the An(IV) model was developed using Th as the An(IV) analog, with application of the results to U(IV), Np(IV) and Pu(IV). Th is considered to be a conservative analog in WIPP solubility calculations because the solubility-limiting solid phases of Th(IV) are more soluble than the analogous U(IV), Np(IV) or Pu(IV) phases (22). Th(IV) forms weaker complexes with ligands than the other An(IV) ions, however performance assessment calculations seek to establish boundary conditions of solubility rather than more accurately representative but less easily defensible sets of speciation conditions. The reactions that are used in the modeling of Th(IV), U(IV), Np(IV) and Pu(IV) with inorganic species are given below:

An0 (am) + 2 H 0 =* An(OH) (aq) 2

An An

4 +

3

4 +

2

+ 5C0 3

4 +

AnC0 (OH) 3

3

6

- An(C0 ) 3

5

2

+ 2 S 0 - ~ An(S0 ) (aq) 4

An

4

2

2

+ 3 S 0 - 10 values. The normalized standard chemical potentials and Pitzer parameters used for modeling speciation and solubility of Np(V) are provided in Tables X through XIII. 2

4

2

3

2

2

+

2

2

3

2

3

+

l n

2

n

2

3


2

3

2

3

+

2

+

5

2

3

+

3

+

5

2

2 +

3

3

l n

2

3

n

2

3

2

3

2

+

2 +

5

2

+

3

3

+

2

2

Additional Modeling Considerations Normalized standard chemical potentials for the WIPP brine components H 0 , H \ N a , K , M g , C a , CI", S0 ", HS0 ", OH", H C 0 " and C 0 " are provided in Table X I V . During the course of a speciation and solubility calculation, the F M T code adjusts brine composition to account for changes in chemistry, such as depletion of M g content in Salado brine as a result of increasing pH due to reaction of M g O with water. Binary and ternary ion interaction parameters for M g * with actinide complexes are not included in the WIPP geochemical model. In general, the impact of the ternary parameters is small, but not negligible. Omission of the binary and ternary parameters for M g has not been viewed as a significant issue due to precipitation of M g at the mildly basic pH of the repository brines. The experimental work of measuring stability constants for actinide-organic ligand interactions at various ionic strengths was carried out at Florida State University by Choppin and coworkers (57). Stability constants of acetate, citrate, oxalate, and E D T A with +

+

2 +

2+

2

2

4

2

4

3

3

2 +

2

2 +

2 +


325 Table X . Normalized Standard Chemical Potentials for Np(V) V

H /RT" Species ft"/RT -369.105 Np0 -366.186 ±2.270 -593.601 -590.563 ± 2.280 Np0 C0 ' -809.832 Np0 (C0 ) -807.134 ±2.293 -1020.214 Np0 (C0 ) ' -1017.704 ±2.313 Np0 OH(aq) -438.730 -435.828 ± 2.784 Np0 (OH) -503.167 ±2.546 -506.238 Np0 OH(am,aged) -454.369 -451.025 ±2.545 Np0 OH(am) -449.643 ±2.317 -452.757 -1048.058 NaNp0 C0 «3.5H 0 -1044.948 ±2.343 -1144.597 Na Np0 (C0 ) (s) -1141.841 ±2.568 -727.330 KNp0 C0 (s) -723.379 ±2.318 -1173.546 K Np0 (C0 ) (s) -1169.574 ±2.326 NEA database values; uncertainties are at 95% confidence limit (77) WIPP values based on referenced work a

Ref. 32 29 29 29 29 29 40 40 40 40 30 30

+

2

2

3

3

2

3

2

3

2

5

3

2

2

2


2

2

2

3

2

3

a b

3

2

+

+

+

+

+

+

+

+

2 +

2 +

2 +

2 +

+

2

+

2

2

3

2

Cation Na Na Na Na K K K K Mg Mg Mg Mg Np0 Np0

2

3

3

2

Table X L Binary Pitzer Parameters for Np(V) 00) 02) C* 0 0 0 0 0.34 0 0.1 0 4.4 0 0.48 0 0 1.8 22.7 0 0 0 0 0 0.34 0 0 0.1 0 4.4 0 0.48 -96 -0.22 2.34 22.7 0 0 0 0 0.34 0 0.1 0 4.4 0 0.48 0 -0.11 -48 2.07 22.7 0.281 0 0.1415 0 cr 0.18 0.0081 0.257 0 C10 "

Anion Np0 (OH) Np0 C0 " Np0 (C0 ) " Np0 (C0 ) Np0 (OH) Np0 C0 ' Np0 (C0 ) " Np0 (C0 ) Np0 (OH) Np0 C0 Np0 (C0 ) " Np0 (C0 ) " 2

Ref 29 29 29 29

2

2

3

3

2

3

2

2

3

3

5

2

2

2

30 30 30

3

3

2

3

2

2

3

3

5

2

2

2

41 41 41 40 40

3

3

2

3

2

2

3

3

5

4

Table X I I . Neutral Ion Interaction Parameter (X) for Np(V) Neutral Species Np0 OH(aq) Np0 OH(aq) Np0 OH(aq) 2

Ion Na

2

CIO4'

2

+

cr

X

0 0

-0.19

Ref 29 29 29


326 Table XIII. Ternary Interaction Parameters for Np(V) ion i

ionj Np0 (OH) " Np0 C0 Np0 (C0 ) Np0 (C0 ) Np0 (C0 ) "

el

2

d

2

er cr co -

3

3

2

3

2

5

2

2

3

3

5

2

3


2

3

3

ion k Na Na Na Na K

e -0.24 -0.21 -0.26 -0.26 -1.9 H

+

+

+

+

+

0 0 0 0 0

Ref. 29 29 29 29 41

Table X I V . Normalized Standard Chemical Potentials of W I P P Brine Components Species H 0 H Na K Mg Ca 2

+

+

+

2 +

2 +

cr so 2

4

HSO4OH-

HC0 3

2

co 3

M°/RT" -95.6635 0 -105.651 -113.957 -183.468 -223.30 -52.955 -300.386 -304.942 -63.435 -236.751 -212.944

ob

AiG -237.14010.041 0 -261.953 ±0.096 -282.510 ± 0 . 1 1 6 -455.375 ± 1.335 -552.806 ± 1.050 -131.217 ± 0.117 -744.004 ±0.418 -755.315 ± 1.342 -157.220 ±0.072 -586.845 ±0.251 -527.900 ± 0.390 m

V°/RT " -95.660610.017 0 -105.67010.039 -113.96310.047 -183.69510.539 -222.99810.424 -52.932 10.047 -300.12610.169 -304.68910.541 -63.42210.029 -236.72910.101 -212.95110.157

a

Reference 19 * Reference 11. NEA database values; the uncertainties are at the 95% confidence limit

+

Th(IV), Np(V) and Am(III) were determined by solvent extraction; M g stability constants with the same ligands were measured by potentiometric titration. Interactions of the organic ligands with M g were added to the database to account for the competitive effect of M g in WIPP brines, especially the Salado brine. The normalized standard chemical potentials for the species that are included in the WIPP geochemical model are reproduced in Tables X V through XVIII. The Pitzer parameters are presented in Tables X I X to X X I . The inclusion of organic ligands does not have a significant effect on the solubility of An(III) and An(IV) under WIPP conditions due to the extensive competition with hydrolysis and carbonate complexation. However, due to the absence of hydrolysis of Np(V) and Pu(V) at pH = 9, it may be anticipated that organic ligand complexation will both enhance the solubility of these species, and enlarge the stability field for the An(V) oxidation state with respect to both pH and Eh. 2 +

2 +


327

Table XV. Normalized Standard Chemical Potentials for Acetate Complexes Species HAc(aq) Ac AmAc ThAc ThAc Np0 Ac(aq) MgAc


2 +

3+

2+

2

2

+

jf/RT -158.300 -147.347 -395.356 -448.525 -604.800 -519.615 -333.346

Ref. 31 31 9 31 42 10 9

Table XVI. Normalized Standard Chemical Potentials for Citrate Complexes Species H Cit(aq) H Cif HCit Cit " AmCit(aq) ThCit NpOzCit MgCif 3

2

2

3

+

2

ff/RT 0 7.476 18.620 33.410 -228.687 -285.898 -343.747 -162.261

Ref_ 31,43 31,43 31,43 31,43 31 31 31 9

Table XVII. Normalized Standard Chemical Potentials for Oxalate Complexes Species H Ox(aq) HOx Ox AmOx' ThOx Np0 Ox MgOx(aq) 2

2

2+

2

lf/RT 0 3.209 13.017 -242.853 -297.428 -365.851 -179.185

Ref 31,43 31,43 31,43 31,44 31,44 31,44 9


328 Table XVIII. Normalized Standard Chemical Potentials for EDTA Complexes Species H EDTA(aq) H EDTA' H EDTA HEDTA EDTA AmEDTA" ThEDTA(aq) Np0 EDTA " MgEDTA ' Np0 H(EDTA) ' Np0 H (EDTA)' 3

2

2

3


4-

3

2

2

2

2

2

Ref 31,43 31,43 31,43 31,43 31,43 31 9 31,45 9 31,45 31,45

ff/RT 0 5.761 12.870 28.710 53.050 -232.977 -285.419 -335.708 -153.734 -351.852 -364.098

4

2

Table XIX. Neutral-Ion Interaction Parameter (k) Neutral Species" HAc H Cit H EDTA H Ox AmCit ThEDTA Np0 Ac MgOx 3

4

2

2

a

Ion cr cr cr cr cr cr cr cr

X 0 0 0 0 -0.406 0.1111 -0.104 0.0189

Ref 31,46 31,43 31,43 31,43 31 9 10 9

all species are aqueous solution species

A speciation and solubility model for An(VI) has not been explicitly developed as it has for An(III), An(IV) and An(V). The only two radionuclides that could reasonably be expected to exist in the hexavalent oxidation state are U and Pu. The current solubility model for U(VI) is based upon a literature survey by Hobart and Moore (/). Studies designed to elucidate thermodynamics of interactions between U(VI) and both inorganic and organic ligands are considerably complicated by the tendency of U(VI) to form polynuclear species. Fortunately, the radioactive inventory of U in the WIPP is small, and U is not an important component in calculating releases from the repository. Additionally, Pu is not expected to persist as Pu(V) or Pu(VI) due to the large amount of metallic Fe that will be present within the WIPP, mitigating the necessity to develop a speciation and solubility model for Pu(VI).


329 Table XX. Ternary Pitzer Parameters Anion i Ac"

Anion j CI'

Cation k Na*

0y -0.09

¥ 0.01029 Utk

Ref. 42,46

Table XXI. Binary Pitzer Parameters for Actinides and Organic Ligands 00) Cation Anion cf Ref. Na Ac0.1426 0.22 0 -0.00629 29, 46 47 Ac 0.1587 0.3251 0 -0.0066 r H 0 0 46 Ac" 0 0 MgAc cr -0.0833 0 0.0987 9 0.29 42 0.4671 1.74 0 0.143 cr ThAc AmAc -0.132 0.309 1.74 0 9 cr Na H Cit" 0.013 31,43 -0.1296 0.29 0 31,43 Na HCit -0.0989 1.74 0 0.027 Na Cit " 0 0.047 31,43 0.0887 5.22 Na MgCif 0.1742 -0.06923 9 0.29 0 ThCit -0.7467 0.29 0 0.319 31 cr Na Np0 Cit ' -0.4226 1.75 0 0.142 31 Na HOx" -0.2448 0 0.068 31,43 0.29 Na Ox -0.2176 1.74 0 0.122 31,43 31,44 ThOx 1.74 0 0.5 -0.343 cr AmOx 31,44 -0.9374 0.29 0 0.248 cr 31,44 Na Np0 Ox" -0.5418 0 0.095 0.29 31,43 Na H EDTA-0.2345 0 0.059 0.29 Na -0.1262 0 0.054 31,43 H EDTA ' 1.74 HEDTA ' 31,43 Na 0.5458 5.22 0 -0.048 Na EDTA " 0 0.001 31,43 1.016 11.6 0.2134 0.00869 9 Na MgEDTA ' 1.74 0 Np0 EDTA 0 31,45 Na 5.911 0 0.683 45 Na Np0 H(EDTA) " 0.4733 -1.504 0 0 45 Na N p 0 H ( E D T A ) " -0.8285 0.2575 0 0.256 Na AmEDTA0.002 31 -0.2239 0.29 0


+

+

+

2+

2

2 +

+

2

+

2

+

3

+

+

+

2

2

+

+

2

2+

+

+

2

+

3

+

2

2

3

+

+

4

+

2

3

+

2

+

2

2

+

2

2

+

Conclusions Normalized standard chemical potentials and Pitzer parameters for the F M T database used in the WIPP geochemical model have been taken from a literature review or programs funded by the WIPP project. The database used in An(III,IV, and V ) speciation and solubility calculations have been reproduced in the present work.


330


Acknowledgments Compilation of the WIPP thermodynamic database is the result of a long term effort with the involvement of numerous individuals; however, three people deserve special recognition: Craig Novak and Emily Giambalvo, both formerly of Sandia National Laboratories and Robert Moore, currently with SNL, carried out a great deal of the work on the database compilation. This research is funded by WIPP programs administered by the U.S. Department of Energy. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy supported this research under contract DE-AC0494AL85000.

References 1.

2.

3.

4.

5.

6.

Hobart, D.E.; Moore, R.C. Analysis of Uranium(VI) Solubility Data for WIPP Performance Assessment: Implementation of Analysis Plan AP-028; Sandia National Laboratories: Albuquerque, N M , Unpublished report on file in the Sandia WIPP Records Center, Carlsbad, N M , as WPO#36488, 1996. Snider, A . C . Verification of the Definition of Generic Weep Brine and the Development of a Recipe for This Brine. Sandia National Laboratories: Carlsbad, N M , Unpublished report on file in the Sandia WIPP Records Center, Carlsbad, N M , as ERMS# 527505, 2003. Popielak, R.S.; Beauheim, R.L.; Black, S.R.; Coons, W.E.; Ellingson, C.T.; Olsen, R . L . Brine Reservoirs in the Castile Formation, Waste Isolation Pilot Plant Project (WIPP), Southeastern New Mexico. T M E 3153. U.S. Department of Energy, Waste Isolation Pilot Plant: Carlsbad, N M , 1983. Novak, C.F. 1996. Predictions of +III, +IV, and +V Actinide Solubilities in WIPP Salado and Castile Brine Using the Revised Thermodynamic Database HMW_Am3Pu3Th4Np5_960823.CHEMDAT. Sandia National Laboratories: Albuquerque, N M , Unpublished memorandum to R . V . Bynum, November 04, 1996. Copy on file in the Sandia WIPP Records Center, Carlsbad, N M , as ERMS# 537331. Novak, C.F.; Moore, R.C. Estimates of Dissolved Concentrations for +III, +IV, +V, and +VI Actinides in a Salado and a Castile Brine under Anticipated Repository Conditions. Sandia National Laboratories: Albuquerque, N M . Unpublished memorandum to M . D . Siegel, March 28, 1996. Copy on file in the Sandia WIPP Records Center, Carlsbad, N M , as ERMS# 236207. Giambalvo, E.R. Recommended Parameter Values for Modeling An(III) Solubility in WIPP Brines. Sandia National Laboratories: Carlsbad, N M .


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Unpublished memorandum to L . H . Brush, July 25, 2002. Copy on file in the Sandia WIPP Records Center, Carlsbad, N M as ERMS# 522982. Giambalvo, E.R. Recommended Parameter Values for Modeling An(IV) Solubility in WIPP Brines. Sandia National Laboratories: Carlsbad, N M . Unpublished memorandum to L . H . Brush, July 26, 2002. Copy on file in the Sandia WIPP Records Center, Carlsbad, N M , as ERMS# 522986. Giambalvo, E.R. Recommended Parameter Values for Modeling An(V) Solubility in WIPP Brines. Sandia National Laboratories: Carlsbad, N M , Unpublished memorandum to L . H . Brush, July 26, 2002. Copy on file in the Sandia WIPP Records Center, Carlsbad, N M as ERMS# 522990. Giambalvo, E.R. Recommended Parameter Values for Modeling Organic Ligands in WIPP Brines. Sandia National Laboratories: Carlsbad, N M , Unpublished memorandum to L . H . Brush, July 25, 2002. Copy on file in the Sandia WIPP Records Center, Carlsbad, N M , as ERMS# 522981. Giambalvo, E.R. Release of FMT Database FMT_021120.CHEMDAT. Unpublished memorandum to L . H . Brush, March 10, 2003. Sandia National Laboratories, Carlsbad, N M . Copy on file in the Sandia WIPP Records Center, Carlsbad, N M , as ERMS# 526372. Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium, and Technetium; Mompean, F., Illemassene, M . , Domenech-Orti, C., Ben Said, K . , Eds. Chemical Thermodynamics Series; V o l . 5, Elsevier: Amsterdam, Netherlands, 2003. Fanghanel, T.; Könnecke, T.; Weger, H.T.; Paviet-Hartmann, P.; Neck, V . ; Kim, J.I. Thermodynamics of Cm(III) in Concentrated Salt Solutions: Carbonate Complexation in NaCl Solutions at 25 °C. J. Solution Chem. 1999, 28 (4), 447-462. Felmy, A.R.; Rai, D.; Fulton, R.W. The Solubility of A m O H C 0 ( c ) and the Aqueous Thermodynamics of the System N a - A m - H C O - C O - O H H O . Radiochim. Acta. 1990, 50 (4), 193-204. Bernkopf, M.F.; Kim, J.I. Hydrolysereaktionen und Karbonatkomplexierung von Dreiwertigem Americium im Naturlichen Aquatischen System; Report RCM-02884; München, Germany, Institut fur Radiochemie Technischen Universitat München, 1984. Giffaut, E. Influence des Ions Chlorure sur la Chimie des Actinides. Effets de la Radiolyse et de la Température. PhD Thesis. Université de Paris-Sud U.F.R. Scientifique D'Orsay, Paris, France, 1994. Fanghänel, T.; Kim, J.I. Spectroscopic Evaluation of Thermodynamics of Trivalent Actinides in Brines. J. Alloys Compd. 1998, 271, 728-737. Fanghänel, T.; K i m , J.I.; Paviet, P.; Klenze, R.; Hauser, W. Thermodynamics of Radioactive Trace Elements in Concentrated Electrolyte Solutions: Hydrolysis of C m in NaCl Solutions. Radiochim. Acta. 1994, 66/67, 81-87. 3

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332 18. Fanghänel, T.; K i m , J.I.; Klenze, R.; Kato, Y . Formation of Cm(III) Chloride Complexes in C a C l Solutions. J. Alloys Compd. 1995, 225, 308311. 19. Könnecke, T.; Fanghänel, T.; K i m , J.I. Thermodynamics of Trivalent Actinides in Concentrated Electrolyte Solutions: Modeling the Chloride Complexation of Cm(III). Radiochim. Acta. 1997,76 (3), 131-135. 20. Harvie, C.E.; Moller, N . ; Weare, J.H. The Prediction of Mineral Solubilities in Natural Waters: The Na-K-Mg-Ca-H-Cl-SO -OH-HCO C O - C O - H O System to High Ionic Strengths at 25 °C. Geochim. Cosmochim. Acta. 1984, 48 (4), 723-751. 21. Rai, D.; Felmy, A.R.; Fulton, R.W. Solubility and Ion Activity Product of AmPO •xH O(am). Radiochim. Acta. 1992, 56 (1), 7-14. 22. Neck, V . ; K i m , J.I. Solubility and Hydrolysis of Tetravalent Actinides. Radiochim. Acta. 2001, 89 (1), 1-16. 23. Östhols, E.; Bruno, J.; Grenthe, I. On the Influence of Carbonate on Mineral Dissolution: III. The Solubility of Microcrystalline ThO in C O H O Media. Geochim. Cosmochim. Acta. 1994, 58 (2), 613-623. 24. Rai, D.; Felmy, A.R.; Moore, D.A.; Mason, M.J. The Solubility of Th(IV) and U(IV) Hydrous Oxides in Concentrated N a H C O and N a C O Solutions. Scientific Basis for Nuclear Waste Management XVIII, Materials Research Society Symposium, Vol. 353, October 23-27, 1994, Kyoto, Japan. Eds. T. Murakami and R.C. Ewing. 1143-1150. 1995 25. Felmy, A.R.; Rai, D.; Sterner, S.M.; Mason, M.J.; Hess, N.J.; Conradson S.D. Thermodynamic Models for Highly Charged Aqueous Species: Solubility of Th(IV) Hydrous Oxide in Concentrated N a H C O and N a C O Solutions. J. Solution Chem. 1997, 26 (3), 233-248. 26. Felmy, A . R . ; Rai, D. A n Aqueous Thermodynamic Model for a High Valence 4:2 Electrolyte T h - S O in the System N a - K - L i - N H - T h S O - H S O - H O . J. Solution Chem. 1992, 21 (5), 407-423. 27. Roy, R.N.; Vogel, K . M . ; Good, C.E.; Davis, W.B.; Roy, L . N . ; Johnson, D.A.; Felmy, A . R . ; Pitzer, K . S . Activity Coefficients in Electrolyte Mixtures: HCl + T h C l + H O for 5-55 °C. J. Phys. Chem. 1992, 96 (26), 11065-11072 28. Felmy, A.R.; Rai, D.; Mason, M.J. The Solubility of Hydrous Thorium(IV) Oxide in Chloride Media: Development of an Aqueous Ion-Interaction Model. Radiochim. Acta. 1991, 55 (4), 177-185. 29. Fanghänel, T.; Neck, V . ; K i m , J.I. Thermodynamics of Neptunium(V) in Concentrated Salt Solutions: II. Ion Interaction (Pitzer) Parameters for Np(V) Hydrolysis Species and Carbonate Complexes. Radiochim. Acta. 1995, 69 (3), 169-176. 30. Novak, C.F.; A l Mahamid, I.; Becraft, K . A . ; Carpenter, S.A.; Hakem, N . ; Prussin, T. Measurement and Thermodynamic Modeling of Np(V) 2

4


3

2

3

2

4

2

2

2

2

3

3

4+

2-

+

+

+

4

2-

4

-

4

2

4

2


+

4

2

3

2

3

4+

333 Solubility in Aqueous K C O Solutions to High Concentrations. J. Solution Chem. 1997, 26 (7), 681-697. Choppin, G.R.; Bond, A . H . ; Borkowski, M . ; Bronikowski, M . G . ; Chen, J.F.; Wall, N . A . ; Lis, S.; Mizera, J.; Moore, R.C. Pokrovsky, O.; Xia, Y . X . Waste Isolation Pilot Plant Actinide Source Term Test Program: Solubility Studies and Development of Modeling Parameters; SAND99-0943; Sandia National Laboratories: Albuquerque, N M , 2001. Fuger, J.; Oetting, F.L. The Chemical Thermodynamics of Actinide Elements and Compounds. Part 2. The Actinide Aqueous Ions. International Atomic Energy Agency, Vienna, Austria, 1976. Morss, L.R.; Williams, C.W. Synthesis of Crystalline Americium Hydroxide, Am(OH) , and Determination of its Enthalpy of Formation; Estimation of the Solubility-Product Constants of Actinide(III) Hydroxides. Radiochim. Acta. 1994, 66/67, 89-93. Chemical Thermodynamics of Americium. Silva, R.J., Bidoglio, G., Rand, M . H . , Robouch, P.B., Wanner, H . , Puigdomenech, I., Eds. Chemical Thermodynamics Series, V o l . 2, Elsevier: Amsterdam, Netherlands, 1995. Rao, L . ; Rai, D.; Felmy, A.R.; Fulton, R.W.; Novak, C.F. Solubility of NaNd(CO ) •6H O in Concentrated N a C O and N a H C O Solutions. Radiochim. Acta. 1996, 75 (3), 141-147. Rai, D.; Felmy, A.; Fulton, R. N d and A m Ion Interactions with Sulfate Ion and Their Influence on NdPO (c) Solubility. J. Solution Chem. 1995, 24 (9), 879-895. Ryan, J.L.; Rai, D. Thorium(IV) Hydrous Oxide Solubility. Inorg. Chem. 1987, 26 (24), 4140-4142. Rai, D.; Felmy, A.R.; Sterner, M.S.; Moore, D.A.; Mason, M.J.; Novak, C.F. The Solubility of Th(IV) and U(IV) Hydrous Oxides in Concentrated NaCl and M g C l Solutions. Radiochim. Acta. 1997, 79 (4), 239-247. Felmy, A.R.; Rai; D. Application of Pitzer's Equations for Modeling the Aqueous Thermodynamics of Actinide Species in Natural Waters: A Review. J. Solution Chem. 1999, 28 (5), 533-553. Neck, V . ; Fanghänel, T.; Rudolph, G.; K i m , J.I. Thermodynamics of Neptunium(V) in Concentrated Salt Solutions: Chloride Complexation and Ion Interaction (Pitzer) Parameters for the N p O Ion. Radiochim. Acta. 1995, 69 (1), 39-47. A l Mahamid, I.; Novak, C.F.; Becraft, K . A . ; Carpenter, S.A.; Hakem, N . Solubility of Np(V) in K - C l - C O and N a - K - C l - C O Solutions to High Concentrations: Measurements and Thermodynamic Model Predictions. Radiochim. Acta. 1998, 81 (2), 93-101. Moore, R.C.; Borkowski, M . ; Bronikowski, M . G . ; Chen, J.; Pokrovsky, O.S.; X i a , Y . ; Choppin, G.R. Thermodynamic Modeling of Actinide Complexation with Acetate and Lactate at High Ionic Strength. J. Solution Chem. 1999, 28 (5), 521-531 2

31.


32.

33.

3

3

34.

35.

3

36.

2

2

2

3 +

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3

3 +

4

37. 38.

2

39.

40.

+

2

41.

3

42.

3



334 43. Mizera, J.; Bond, A . H . ; Choppin, G.R.; Moore, R.C. Dissociation Constants of Carboxylic Acids at High Ionic Strengths. In Actinide Speciation in High Ionic Strength Medi; Reed, D.T., Ed.; Kluwer Academic/Plenum Publishers: New York, N Y , 1999;113-124. 44. Borkowski, M . ; Moore, R.C.; Bronikowski, M . ; Chen, J.F.; Pokrovsky, O.S.; X i a , Y . X . ; Choppin, G.R. Thermodynamic Modeling of Actinide Complexation with Oxalate at High Ionic Strength. J. Radioanal Nucl. Chem. 2001, 248 (2), 467-471. 45. Pokrovsky, O.S.; Bronikowski, M . ; Moore, R.C.; Choppin, G.R. Interaction of Neptunyl(V) and Uranyl(VI) with E D T A in NaCl Media: Experimental Study and Pitzer Modeling. Radiochim. Acta. 1998, 80 (1), 23-29. 46. Novak, C.; Borkowski, M . ; Choppin, G . Thermodynamic Modeling of Neptunium(V)-Acetate Complexation in Concentrated NaCl Media. Radiochim. Acta. 1996, 74, 111-116. 47. Pitzer, K . Ion Interaction Approach: Theory and Data Correlation. In Activity Coefficients in Electrolyte Solutions, 2nd Edition; Pitzer, K . , Ed.; C R C Press: Boca Raton, FL, 1991; pp 75-153


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