Determination of uranium(IV) hydrolysis constants and solubility product of UO2•xH2O

The hydrolysis constants of tetravalent uranium were determined by a solvent extraction method using thenoyltrifluoroacetone(TTA) and U-233. The distribution ratio of U(IV) was measured as a function of the pH, value in the aqueous phase at I = 0.1, 0.5 and 1.0, and was analyzed to obtain the hydrolysis constants (beta(m)) of U(OH)(m)((4-m)+) at the standard state (I = 0). By taking the specific ion interaction theory (SIT) for ionic strength corrections, the hydrolysis constants at I = 0 were determined to be beta(1)degrees = 13.71 +/- 0.31, beta(2)degrees = 26.12 +/- 0.21 and beta(3)degrees = 36.85 +/- 0.36, together with the ion interaction coefficients of UOH3+, U(OH)(2)(2+) and U(OH)(3)(+). The solubility product (K-sp) for the reaction of UO2.XH2O = U4+ + 4OH(-) + (x - 2)H2O was also calculated to be log K(sp)degrees = -53.93 +/- 0.20 by considering the hydrolysis constants.