The solubility of U(IV) hydrous oxide in concentrated NaCl and MgCl2 solutions

The solubility of UO2 sm-bullet xH2O(am) was studied in 0.2, 1.0, and 6.0 molal NaCl, and in 1.0, 2.0, and 3.0 molal MgCl2 aqueous solutions over a range of hydrogen ion concentrations. Extreme precautions were taken to ensure that the dissolved uranium was present as U(IV). Limited oxidation state analyses, systematic trends in the U(IV) solubility data, and comparisons with prior literature studies that used the same experimental procedure indicated that the dissolved U was present as U(IV). The aqueous U concentrations in a given NaCl solution at equilibration periods ranging up to about 35 days were similar, indicating that steady-state concentrations are reached within a day in most cases. This result is consistent with our earlier data in dilute solutions. The observed U concentrations decrease with the increase in pcH+ in both the NaCl and MgCl2 solutions. At a given pcH+ value, the observed U concentrations in 0.2 m NaCl are about an order of magnitude higher than those in 1.0 and 6.0 m NaCl. The solubility of UO2 sm-bullet xH2O(am) in 1.0 and 6.0 m NaCl and 1.0, 2.0, and 3.0 m MgCl2 solutions, however, are similar to each other