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

Summary The hydrolysis constants of tetravalent uranium were determined by a solvent extraction method using thenoyltrifluoroacetone(TTA) and233U. The distribution ratio of U(IV) was measured as a function of the pHcvalue in the aqueous phase atI=0.1, 0.5 and 1.0, and was analyzed to obtain the hydrolysis constants (βm) 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 atI=0 were determined to beβ1°=13.71±0.31,β2°=26.12±0.21 andβ3°=36.85±0.36, together with the ion interaction coefficients of UOH3+, U(OH)22+and U(OH)3+. The solubility product (Ksp) for the reaction of UO2·xH2O=U4++4OH-+ (x-2)H2O was also calculated to be logKsp° =-53.93±0.20 by considering the hydrolysis constants.