Interaction of neptunium and technetium with UO 2+ x

Interaction of uranium dioxide with highly mobile radionuclides 237 Np and 99 Tc was studied under oxidative conditions. Sorption of these radionuclides at different pH was measured, and the mechanism of redox reaction occurring in the course of their sorption were determined. In alkaline solution, Np(V) is reduced on the UO 2+ x surface and is sorbed in the form of tetravalent species. In neutral solutions, Np is sorbed in the form of Np(V). This is due to the fact that the stoichiometry of the UO 2+ x surface corresponds to U 4 O 9 . In acid solution, U(VI) is leached to form surface UO 2 . Although the free surface area of a UO 2+ x sample is low, the Np distribution coefficients K d at pH > 6 are relatively high: log K d > 2. Unlike Np, Tc(VII) is not reduced on the UO 2+ x surface. However, the sorption capacity of uranium dioxide for Tc(IV) is high.