Photochemically induced reductions of trace Np(VI) in U(VI)-HNO3 solutions

Dilute Np(VI) can be reduced to Np(V) in the presence of large amounts of UO2(NO3)2 by a photochemical reaction which first involves the photo-reduction of NO3- to NO2-. Although UO22+ competes strongly for photons, the accompanying stabilization of Np(V) by UO22+ tends to compensate for the UO22+ screening effect. Experiments have been performed using 254 and 300 nm radiation on 0.1 and 1.0 M HNO3 solutions containing 1 M UO2(NO3)2 and either 0.01 or 0.001 M NpO22+. Because the primary photochemical reaction involves photo-reduction of NO3- to NO2-, still lower concentrations of Np(VI) are expected to be reducible by this process. (author)