No abstract available

[en] 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 CO₂(g) (0.003 or 0.03 atm.), and as functions of K₂CO₃ concentrations (0.01 to 5.8 mol · kg^-1) in the presence of 0.01 mol · dm^-3 KOH and KHCO₃ concentrations (0.001 to 0.826 mol · kg^-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)(CO₃)₂^2- and Cr(OH)₄CO₃^3-] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO₂(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log₁₀ K^o values of reactions involving these species [{Cr(OH)₃(am) + 2CO₂(g) (r_equilibrium) Cr(OH)(CO₃)₂^2- + 2H⁺} and {Cr(OH)₃(am) + OH^- + CO₃^2- (r_equilibrium) Cr(OH)₄CO₃^3-] 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