Uranium(IV) Solubility and Hydrolysis Constants Under Reduced Conditions

Abstract

AbstractThe solubility of UO2 (s) was examined in dilute NaCl solutions at room temperature and in the pH range from 2 to 12. Dissolution equilibrium showed good agreements between the data obtained by oversaturation and undersaturation experiments.The dissolution reactions that control the solubility of U[IV] are estimated as UO2 (s) + 4H+ → U4+ + 2H2O and UO2 (s) + 2H2O → U(OH)4°. The log K at zero ionic strength are yielded 0.34 ± 0.4 and −8.7 ± 0. 4, respectively. The hydrolysis constant (log β14) is calculated −9.0 ± 0.5 for the hydrolysis reaction of U4+ + 4H2) → U(OH)4° + 4H+. Contribution of the other uranium species to the solubility are of minor importance.The crystallization of the precipitations of U02 (s) progressed gradually in the oversaturation experiments. Nevertheless the progress of crystallization had little effect on the solubility.