The Effect of Solvents on the Adduct Formation of Uranyl Thenoyltrifluoroacetonate with Tributyl Phosphate

Addition compound formation between uranyl bis-thenoyltrifluoroacetonate (UO2A2) and tributyl phosphate(S) was studied by a partition method, using uranium-237 as the tracer. The formula of the adduct complex was shown to be UO2A2·S. The solvent effect on the adduct formation constant was taken into account in connection with the activity; the activity coefficients of each species in various solutions were calculated from the molar volume and the solubility parameter. The formation constants based on the molar fraction, Kx, in a number of solvents were pre-estimated, employing logKx=7.08 in carbon tetrachloride as a reference. They are in agreement with the observed values. The formation constant in terms of activity was found to be constant logKS°=5.77±0.30. A correlation between the formation constants of the two adducts, UO2A2·S and ZnA2·S, was demonstrated.