Decontamination of uranium oxides from solid wastes by supercritical CO2 fluid leaching method using HNO3-TBP complex as a reactant

A new method referred to as supercritical CO2 fluid leaching (SFL), which is based on selective dissolution of uranium oxides with the supercritical CO2 fluid containing the HNO3-tri-n-butyl phosphate (TBP) complex, has been developed for the removal and recovery of uranium from solid wastes contaminated by uranium oxides. A recommended SFL procedure has been established consulting experimental results of the complexation efficiency of the uranium oxides and the dissolution efficiency of U(VI)-TBP complex at different pressures. The recommended method consists of complexation process at 60degreesC and 15 MPa for 150 min using the supercritical CO2 containing the HNO3-TBP complex and dissolution process at 60degreesC and 20 MPa using a flow of the neat supercritical CO2. The complexation-dissolution cycle is repeated twice. The feasibility of the recommended procedure to the removal of uranium from the solid wastes was demonstrated using synthetic wastes that were a mixture of standard sea sand (50 g) and UO2 or U3O8 powders (20-200 mg of U). The decontamination factor Of UO2 or U3O8 was determined to be higher than 5 x 10(2). The solid waste after the SFL treatment was dry and contained enough low concentrations of TBP and HNO3. (C) 2003 Elsevier B.V. All rights reserved.