Sonochemical dissolution of metallic plutonium in a mixture of nitric and formic acid

The dissolution of pure plutonium metal reference material (99.977%) in a HNO3-HCOOH mixture is considerably enhanced by ultrasonic irradiation with intensity 1 W/cm2 and frequency 20 kHz under an argon atmosphere. The tested medium is potentially suitable for preparing standard plutonium solution. At [HNO3] = 0.5-1.0 M and [HCOOH] = 1.0-2.0 M the rate of sonochemical dissolution is as much as 17 times higher than that for the unsonicated process. The dissolution of plutonium metal without sonication leads to Pu(III) accumulation in solution. Under sonication at [HNO3] ≥ 1 M Pu(III) is oxidized to Pu(IV) due to HNO2 accumulation as a result of HNO3 sonolysis. It is assumed that ultrasound removes the passivating layer from the metal surface and accelerates of the mass-transfer processes near the extended liquid-solid interface. The formation of CO2 under sonication of HNO3-HCOOH mixtures shows that slow sonochemical denitration also occurs in the system investigated. (orig.)