Photolysis of Uranium, Neptunium, and Plutonium Ions in Propionic Acid Solutions

The photolytic reactions of U(VI), Np(VI, V), and Pu(VI) in 0.5–13 M C₂H₅COOH solutions were studied. Under UV irradiation, U(VI) is reduced to U(IV); Np(VI), to Np(V); Np(V), to Np(IV); and Pu(VI), to Pu(IV) and Pu(III). The photochemical reduction of U(VI) in concentrated propionic acid to U(IV) under UV irradiation is fast and complete. The Np(V) reduction proceeds with an induction period, after which the reaction accelerates. This is due to the fact that Np(V) weakly absorbs in the UV range. The appearance of Np(IV) leads to the formation of a Np(V)–Np(IV) cation–cation complex. The complex absorbs light, its energy excites Np(V), and Np(V) reacts with the acid. The photoreduction of Np(VI) proceeds without an induction period, because Np(VI) significantly absorbs UV light. Pu(VI) under UV irradiation is reduced to Pu(IV) and finally to Pu(III).