A CRITICAL REVIEW OF THERMODYNAMIC DATA FOR INORGANIC TIN SPECIES

Abstract

The accuracy of published inorganic tin thermodynamic data was evaluated to obtain a reliable basis for modeling Sn migration in a deep repository of radioactive waste. Hydrolysis, complexation with halide ions or other inorganic compounds, and precipitation reactions of Sn(II) and Sn(IV) were studied. The Guggenheim-Scatchard Specific Interaction Theory was used to correct equilibrium constant to zero ionic strength.Tin(II) can be hydrolysed into SnOH+, Sn(OH)20 and Sn(OH)3- at low concentration. For higher tin levels, the Sn2(OH)22+ and Sn(OH)42+ polynuclear species are predominant. Stability constants of these equilibria at the standard state were evaluated from data available in the literature and recommended values are proposed. Complexation reactions between tin(II) and halide ions are well known, but the complex species formed are only present in solution when halide concentration is > 10-3 mol L-1 and at pH values < 4. In the presence of sulphides, selenides, or tellurides, the stannous ions form very stable solid phases. Because of the very low solubility of SnO2(s), little information is available in the literature about Sn(IV) hydrolysis, complexation, or precipitation reactions.