SONOCHEMICAL DISSOLUTION OF METALLIC PLUTONIUM IN A MIXTURE OF NITRICAND FORMIC-ACID

The dissolution of pure plutonium metal reference material (99.977%) i n a HNO3-HCOOH mixture is considerably enhanced by ultrasonic irradiat ion with intensity 1 W/cm(2) and frequency 20 kHz under an argon atmos phere. The tested medium is potentially suitable for preparing standar d plutonium solution. At [HNO3] = 0.5-1.0 M and [HCOOH] = 1.0-2.0 M th e rate of sonochemical dissolution is as much as 17 times higher than that for the unsonicated process. The dissolution of plutonium metal w ithout sonication leads to Pu(III) accumulation in solution. Under son ication at [HNO3] greater than or equal to 1 M Pu(III) is oxidized to Pu(IV) due to HNO2 accumulation as a result of HNO3 sonolysis. It is a ssumed that ultrasound removes the passivating layer from the metal su rface 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 i n the system investigated.