Efficient removal of radioactive Th(IV) and U(VI) from rare earth leaching solution using HDES

The hydrophobic deep eutectic solvents (HDES) with low viscosity, density and environmental friendliness have been prepared and characterized based on trioctylphosphine oxide (TOPO) and N,N -dihexyl succinamic acid (DHSCA), which were used as both extractant and organic phase for highly efficient removal of radioactive elements of U(VI) and Th(IV) from rare earth (RE) leaching solution. The extraction efficiency of U(VI) and Th(IV) exceeded 99 % by a single stage extraction. Benefiting from the blocking effect of hydrogen bonding on P = O and the good affinity of DHSCA and TOPO for actinides, the present HDES exhibited the excellent extraction selectivity for U(VI) and Th(IV) over Fe(III), Al(III), Mg(II), Ca(II) and RE(III). Even after seven extraction-stripping cycles, the prepared HDES could still effectively remove radioactive U(VI) and Th(IV) from RE leaching solution. The co-extracted U(VI) and Th(IV) was further separated and enriched by two successive stripping steps. Using the slope analysis, 31 P NMR and FT-IR spectra, the stoichiometry of extracted species and the extraction mechanism of HDES to Th(IV) and U(VI) were evaluated. Due to the superior extraction efficiency, excellent environmental compatibility and sustainability, the present approach offers a practical alternative for removal of radioactive elements from rare earth minerals.