Toward Innovative Actinide Separation Processes: Sequential Reduction Scheme of Uranium, Neptunium, and Plutonium in 3 M HNO3 by External Ultrasound Irradiation

Abstract

An innovative remote valency control technique for actinide ions induced by external ultrasound irradiation was reported in the present study. It is known that ultrasound irradiation to water causes the oxidation and/or reduction of the solute by H• or OH• There were some reports on the redox behavior of actinide elements under ultrasound irradiation. Nevertheless, they showed that the ability of ultrasound is not sufficient for the use of the actinide separation processes. However, very recently we found that a noble metal catalyst drastically enhances the sonochemical effect and that even highly stable U(VI) is reduced to U(IV) by ultrasound irradiation. Employing this catalytic reaction, we are developing low-emission actinide ion separation schemes driven by external ultrasound irradiation. In the present work, U(VI), Np(VI) and Pu(VI) in 3 M HNO3 medium were chosen as target ions. Their valency was first adjusted to U(VI)/Np(V)/Pu(IV) by external ultrasound irradiation and, then, further sonochemical reduction to U(IV)/Np(IV)/Pu(III) was carried out. The present results confirmed the possibility to design the low-emission U/Np/Pu mutual separation scheme driven by external ultrasound irradiation.