Redox Kinetics of U,Pu, and Np in TBP Solutions: VI. Reactions of Neptunium and Plutonium with Organic Reducing Agents: Determination of the Final Oxidation States and Reaction Rates

Reactions of Pu(IV) and Np(VI) with organic reducing agents of various types (substituted hydroxylamines, oximes, aldehydes, etc.) in tributyl phosphate solutions containing nitric acid were studied spectrophotometrically. The molar extinction coefficients of neptunium and plutonium in various oxidation states [Np(IV,V,VI), Pu(III,IV,VI)] in TBP solutions were determined as influenced by HNO₃ and H₂O concentrations and temperature. It was found that organic reducing agents at low HNO₃ concentration convert plutonium and neptunium to Pu(III) and Np(V), respectively. With increasing HNO₃ concentration Pu(III) and Np(V) are partly oxidized back to Pu(IV) and Np(VI), respectively, by reaction with nitrous acid. The rate constants of Pu(VI) and Np(VI) reduction and Np(V) oxidation as influenced by concentration of organic reducing agents and HNO₃ were evaluted from the kinetic data.