Plutonium(IV) peroxide formation in nitric medium and kinetics Pu(VI) reduction by hydrogen peroxide

Reduction of plutonium (VI) to Pu(IV) with hydro gen peroxide is a step in industrial processes used to purify plutonium nitrate solutions. This opera tion must be carefully controlled, in order to avoid any formation of the P u(IV) peroxide green precipitate and to obtain exclusively Pu(IV). This led us to study the acidity and Pu and H2O2 concentrations influences on the p recipitate appearance and to perform a Pu(VI) reduction kinetic study on a wide range of acidities ([HNO3]: 0.5 to 8M), plutonium concentrations ([Pu( Vl)]: 0.1 to 0.8 M) and [H2O2]/[Pu(VI)] ratio (from 1 to 8). Thus, the doma in of Pu(IV) peroxide formation and the reactional paths were established. With the exception of 0.5 M nitric acid medium, the kinetic curves show two distinct regims: the first one corresponds to an induction period where th e Pu(VI) concentration doesn't change, the second corresponds to a linear d ecrease of Pu(VI). An increase of the temperature greatly accelerates the P u(VI) reduction rate while [H2O2]/[Pu(VI)] has almost no influence. The Pu( VI) total reduction time decreases when initial concentration of plutonium increases. By increasing nitric acid concentration from 0.5 M to 6 M, the t otal Pu(VI) reduction time decreases. This time increases when [HNO3] varie s from 6M to 8M.