Thermal treatment for the detachment of RE-rich particles precipitated by the high-temperature oxidation of (U,RE)3O8 powder

Abstract

In this study, the thermal detachment of rare earth (RE)-rich particles adhered to RE-poor particles separated by the high-temperature oxidation of (U,RE)3O8 powder was investigated by repeated oxidation after reduction at low temperature using air and ozone as oxidizing agents. The RE-rich particles detached from RE-poor particles were collected using a magnet of 0.8T. The relative degree for the detachment and collection of RE-rich particles from RE-poor particles was evaluated by the observation of particle morphologies by SEM. As most of the RE-poor U3O8 particles during oxidation at low temperature were broken into plates, the detachment of RE-rich particles from RE-poor particles increased with increasing RE-rich particle sizes dependent on the oxidation temperature of (U,RE)3O8 powder. The detachment of the RE-rich particles increased with decreasing oxidation temperature from 500 to 360°C under air. Under ozone, the (U,RE)O2 pellets, RE-rich and poor UO2 particles, and RE-rich U4O9 particles were not oxidized, while the RE-poor U3O8 particles were converted to the RE-poor UO3 particles with very low magnetic susceptibility. The collection of RE-rich particles increased with increasing magnetic susceptibility difference between the RE-rich and RE-poor particles.