Chromium(III) hydroxide solubility in the aqueous K{sup +}-H{sup +}-OH{sup_}-CO{sub 2}-HCO{sub 3}{sup -}CO{sub 3}{sup 2-}-H{sub 2}O system : a thermodynamic model.
Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3-13) at two different fixed partial pressures of CO{sub 2}(g) (0.003 or 0.03 atm.), and as functions of K{sub 2}CO{sub 3} concentrations (0.01 to 5.8 mol {center_dot} kg{sup -1}) in the presence of 0.01 mol {center_dot} dm{sup -3} KOH and KHCO{sub 3} concentrations (0.001 to 0.826 mol {center_dot} kg{sup -1}) at room temperature (22 {+-} 2 C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO{sub 3}){sub 2}{sup 2-} and Cr(OH){sub 4}CO{sub 3}{sup 3-}] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO{sub 2}(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log{sub 10} K{sup o} values of reactions involving these species [{l_brace}Cr(OH){sub 3}(am) + 2CO{sub 2}(g) {r_equilibrium} Cr(OH)(CO{sub 3}){sub 2}{sup 2-} + 2H{sup +}{r_brace} and {l_brace}Cr(OH){sub 3}(am) + OH{sup -} + CO{sub 3}{sup 2-} {r_equilibrium} Cr(OH){sub 4}CO{sub 3}{sup 3-}] were found to be ?(19.07 {+-} 0.41) and ?(4.19 {+-} 0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); EM
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 929239
- Report Number(s):
- ANL/XSD/JA-58743; JSLCAG; TRN: US0804087
- Journal Information:
- J. Solution Chem., Vol. 36, Issue 10 ; Oct. 2007; ISSN 0095-9782
- Country of Publication:
- United States
- Language:
- ENGLISH
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