Behaviors of plutonium and neptunium in nitric acid solutions containing hydrazine and technetium ions

Abstract

The valence behaviors of plutonium and neptunium in the interaction of Pu(IV) and Np(V) with hydrazine and tetravalent uranium in technetium(VII)-containing aqueous nitric acid are reported. At [HNO3] = 1 mol/l and Pu(IV) and Tc(VII) concentrations of ∼0.1 and 0.01–0.2 mol/l, respectively, Pu(IV) is reduced to Pu(III) and is then entirely reoxidized to Pu(IV). Neptunium(V) in 1–3 M HNO3 undergoes reduction to Np(IV) and then turns back into Np(V). The resulting solution usually contains a mixture of Np(IV) and Np(V). The reduction of Pu(IV) to Pu(III) and the reduction of Np(V) to Np(IV) are accompanied by hydrazine decomposition and by the reduction of most of the Tc(VII) to its lower valence forms. The conversions of Pu(III) into Pu(IV) and of Np(IV) into Np(V) are accompanied by the oxidation of these forms of technetium to Tc(VII). The introduction of diethylenetriaminepentaacetic acid into the reaction system makes Pu(III) more stable against reoxidation into Pu(IV) by reducing the hydrazine decomposition rate, enhances the conversion of Np(V) into Np(IV), and hampers Np(IV) oxidation to Np(V).