Removal of thorium and uranium from leach solutions of ion-adsorption rare earth ores by solvent extraction with Cextrant 230

The removal of radioactive elements thorium and uranium from the leach solution of ion-adsorption rare earth ores by aluminum sulfate was studied using di(2-ethylhexyl) [N-(2-ethylhexyl)aminomethyl] phosphonate (Cextrant 230, L).The extraction of thorium, uranium, rare earths, aluminum and other elements was investigated in detail, especially for uranium. The extracted complex was inferred to be UO2SO4·2L, in which phosphoryl oxygen atom of Cextrant 230 was involved in the coordination of UO22+. The thermodynamic parameters, such as ΔH, ΔG, ΔS were calculated. The negative value of ΔH suggests that the extraction of U(VI) by Cextrant 230 is an exothermic process. The extraction capacities of 5% (v/v) Cextrant 230 for Th(IV) and U(VI) were determined to be 4.08 g/L and 6.16 g/L, respectively. The loaded U(VI) and Th(IV) can be stripped using common inorganic acids. By just one stage extraction, the concentrations of thorium and uranium in the simulated leaching solution decreased obviously from 2.73 mg/L and 0.82 mg/L to <0.1 mg/L.