Sonochemical redox reactions of Pu(III) and Pu(IV) in aqueous nitric solutions

This study investigates the behavior of plutonium ions Pu(IV) and Pu(III) in aqueous nitric solutions subjected to ultrasound irradiation at 20 kHz. The objective was to understand the effects of ultrasound on the redox processes of these two oxidation states. Methodologically, experiments examined the reactions in the absence and presence of anti-nitrous reagents, such as sulfamic acid or hydrazinium nitrate. Results show that, in the absence of such reagents, ultrasound does not affect Pu(IV); however, Pu(III) is rapidly oxidized to Pu(IV) due to the autocatalytic generation of HNO2 from HNO3 sonolysis. In the presence of anti-nitrous reagents, Pu(IV) can be reduced to Pu(III) through a first-order reaction, establishing a steady state of coexistence for both oxidation states. Notably, the reduction is linked to the sonochemical generation of H2O2, though the kinetics of Pu(IV) reduction exceeds those of H2O2 formation, which is hypothesized to result from titanium erosion of the sonotrode. Titanium particles can solubilize under ultrasound, producing Ti(III), a potent reducing agent for Pu(IV).