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Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Kitamura A.,Japan Atomic Energy Agency | Yoshikawa H.,Japan Atomic Energy Agency | Felmy A.R.,Pacific Northwest National Laboratory
Journal of Solution Chemistry | Year: 2013

The major objective of this study, based on critical review and experimental studies, was to develop a reliable thermodynamic model for the Nd-F system at 25 C. The SIT model was used to convert concentration constants reported in the literature to constants at zero ionic strengths for cross comparison and selection of reliable values. The critically evaluated thermodynamic constants for the formation of NdF2+ and NdF 2 + were then used to interpret the extensive NdF 3(cr) solubility data in NaF and NH4F solutions, ranging in concentrations from extremely low values to as high as 1.0 mol·kg -1, equilibrated for different periods ranging up to as long as 72 days. These efforts have resulted in 10 βn 0 for the reaction [Nd3+ + nF- ⇌ NdF n 3-n ] of (3.81 ± 0.10), (5.89 ± 0.77), and <12.48 for n values of 1-3, respectively. The 10 K sp 0 for the solubility of NdF3(cr) (NdF3(cr) ⇌ Nd3+ + 3F-) was determined to be (-20.49 ± 0.37). Because (1) Nd is an excellent analog for trivalent actinides - An(III) (i.e.; Pu(III), Am(III), and Cm(III)), and (2) the available data for the An(III)-F system, especially the solubility products of AnF3(cr), are of extremely poor quality, the critical literature review in combination with the experimental Nd-F system data have been used to assign thermodynamic constants for the An(III)-F reactions until good quality specific data for them becomes available. © 2013 Springer Science+Business Media New York.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Moore D.A.,Pacific Northwest National Laboratory
Journal of Solution Chemistry | Year: 2012

Prior to this study there were no thermodynamic data for isosaccharinate (ISA) complexes of Fe(III) in the environmental range of pH (>~4.5). This study was undertaken to obtain such data in order to predict Fe(III) behavior in the presence of ISA. The solubility of Fe(OH)3(2-line ferrihydrite), referred to as Fe(OH)3(s), was studied at 22 ± 2 C in: (1) very acidic (0.01 mol·dm-3 H+) to highly alkaline conditions (3 mol·dm-3 NaOH) as a function of time (11-421 days), and fixed concentrations of 0.01 or 0.001 mol·dm-3 NaISA; and (2) as a function of NaISA concentrations ranging from approximately 0.0001 to 0.256 mol·dm-3 and at fixed pH values of approximately 4.5 and 11.6 to determine the ISA complexes of Fe(III). The data were interpreted using the SIT model that included previously reported stability constants for Fe(ISA)n 3-n (with n varying from 1 to 4) and Fe(III)-OH complexes, and the solubility product for Fe(OH)3(s) along with the values for two additional complexes (Fe(OH)2(ISA)(aq) and Fe(OH)3(ISA)2 2- determined in this study. These extensive data provided a log10 K 0 value of 1.55 ± 0.38 for the reaction Fe3++ ISA- + 2H 2O ⇄ Fe(OH)2(ISA(aq) + 2H+) $$ and a value of -3.27 ± 0.32 for the reaction (Fe 3++ 2ISA- + 3H2O ⇄ Fe(OH) 3(ISA)2 2-+ 3H+ and show that ISA forms strong complexes with Fe(III) which significantly increase the Fe(OH) 3(s) solubility at pH <∼12. Thermodynamic calculations show that competition of Fe(III) with tetravalent ions for ISA does not significantly affect the solubilities of tetravalent hydrous oxides (e.g.; Th and Np(IV)) in ISA solutions. © 2012 Springer Science+Business Media New York.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Schaef H.T.,Pacific Northwest National Laboratory | Kitamura A.,Japan Atomic Energy Agency
Journal of Solution Chemistry | Year: 2011

The solubility of SnO2(cassiterite) was studied at 23 ± 2 °C as a function of time (7 to 49 days) and pH (0 to 14.5). Steady state concentrations were reached in <7 days. The data were interpreted using the SIT model. The data show that SnO2(cassiterite) is the stable phase at pH values of <∼11.7. These extensive data provided a log 10K0 value of -64.39 ± 0.30 for the reaction (SnO2(cassiterite) +2H2O ⇄ Sn4+ + 4OH-) and values of 1.86 ± 0.30, ≤-0.62, -9.20 ± 0.34, and -20.28 ± 0.34 for the reaction (Sn4+ + nH2O ⇄ Sn(OH)4-n n + nH+) with values of "n" equal to 1, 4, 5, and 6 respectively. These thermodynamic hydrolysis constants were used to reinterpret the extensive literature data for SnO2(am) solubility, which provided a log10K0 value of -61.80 ± 0.29 for the reaction (SnO2(am) + 2H2O ⇄ Sn4+ + 4OH-). SnO2(cassiterite) is unstable under highly alkaline conditions (NaOH concentrations >0.003 mol·dm-3) and transforms to a double salt of SnO2 and NaOH. Although additional well-focused studies will be required for confirmation, the experimental data in the highly alkaline region (0.003 to 3.5 mol · dm-3 NaOH) can be well described with log10K0 of -5.29 ± 0.35 for the reaction Na2Sn(OH)6(s) ⇄Na2Sn(OH)6(aq). © Springer Science+Business Media, LLC 2011.


Rai D.,Rai Enviro Chemical LLC | Yui M.,Japan Atomic Energy Agency | Schaef H.T.,Pacific Northwest National Laboratory | Kitamura A.,Japan Atomic Energy Agency
Journal of Solution Chemistry | Year: 2010

Prior to this study no data for the solubility product of BiPO 4(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO4(cr) was studied at 23 ± 2 °C from both the over- and under-saturation directions as functions of a wide range in time (6-309 days), pH values (0-15), and phosphate concentrations (reaching as high as 1.0 mol.kg-1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in <6 days. The data were interpreted using the SIT model. These extensive data provided a solubility product value for BiPO4(cr) and an upper limit value for the formation of BiPO4(aq). Because the aqueous system in this study involved relatively high concentrations of chloride, reliable values for the complexation constants of Bi with chloride were required to accurately interpret the solubility data. Therefore as a part of this investigation, existing Bi-Cl data were critically reviewed and used to obtain values of equilibrium constants for various Bi-Cl complexes at zero ionic strength along with the values for various SIT ion interaction parameters. Predictions based on these thermodynamic quantities agreed closely with our experimental data, the chloride concentrations of which ranged as high as 0.7 mol.kg-1. The study showed that BiPO4(cr) is stable at pH values <9.0. At pH values >9.0, Bi(OH)3(am) is the solubility controlling phase. Reliable values for the Bi(OH)3(am) solubility reactions involving Bi(OH) 3(aq) and Bi(OH)- 4 and the formation constants of these aqueous species are also reported. © Springer Science+Business Media, LLC 2010.


Rai D.,Rai Enviro Chemical LLC | Felmy A.R.,Pacific Northwest National Laboratory | Moore D.A.,Pacific Northwest National Laboratory | Kitamura A.,Japan Atomic Energy Agency | And 3 more authors.
Radiochimica Acta | Year: 2014

The aqueous solubility of BaSeO 4 (cr) was studied at 23 ± 2 °C as a function of Na 2 SeO 4 concentrations (0.0001 to 4.1mol kg -1) and equilibration periods (3 to 596 d). The equilibrium, approached fromboth the underand over-saturation directions, in this systemwas reached rather rapidly (=3 d). The SIT and Pitzer's ion-interaction models were used to interpret these data and the predictions based on both of these models agreed closely with the experimental data. Thermodynamic analyses of the data show that BaSeO 4 (cr) is the solubility-controlling phase for Na 2 SeO 4 concentrations <0.59mol kg -1. The log 10 t0 value for the BaSeO 4 (cr) solubility product (BaSeO 4 (cr) → Ba 2+ + SeO 4 2-) calculated by the SIT and Pitzer models were very similar (-7.32 ± 0.07 with Pitzer and -7.25 ± 0.11 with SIT). Although the BaSeO 4 (cr) solubility product and Ba concentrations as a function of Na 2 SeO 4 concentrations predicted by both the SIT and Pitzer models are similar, the models required different sets of fitting parameters. For examples, 1) interpretations using the SITmodel required the inclusion of Ba(SeO 4 ) 2 2- species with log 10 t 0 = 3.44±0.12 for the reaction (Ba 2+ + 2SeO 4 2- → Ba(SeO 4 ) 2 2-), whereas these species are not needed for Pitzer model, and 2) at Na 2 SeO 4 concentrations >0.59mol kg-1 it was also possible to calculate the value for log 10 → 0 for the solubility product of a proposed double salt (Na 2 Ba(SeO 4 ) 2 (s) → 2Na+ +Ba2+ +2SeO 4 2-) which for the SIT model is -(8.70 ± 0.29) whereas for the Pitzer model it is -(9.19 ± 0.19). The ion-interaction/ionassociation parameters hitherto unavailable for both the SIT and Pitzer models required to fit these extensive data extending to as high ionic strengths as 12.3mol kg-1 were determined. The model developed in this study is consistent with all of the reliable literature data, which was also used to extend themodel to bariumconcentrations as high as 0.22 mol kg-1 and pH ranging from 1.4 to 13.8, in addition to selenium concentrations as high as 4.1mol kg -1. © 2014 Oldenbourg Wissenschaftsverlag GmbH, Munchen.

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