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Variation of stability constants of thorium citrate complexes and of thorium hydrolysis constants with ionic strength

Choppin, G.R.

Citrate is among the organic anions that are expected to be present in the wastes planned for deposition in the Waste Isolation Pilot Plant repository. In this study, a solvent extraction method has been used to measure the stability constants of Thorium(IV)[Th(IV)] with citrate anions in aqueous solutions with (a) NaClO{sub 4} and (b) NaCl as the background electrolytes. The ionic strengths were varied up to 5 m (NaCl) and 14 m (NaClO{sub 4}). The data from the NaClO{sub 4} solutions at varying pH values were used to calculate the hydrolysis constants for formation of Th(OH){sup 3+} at the different ionic strengths.