Investigation on the recovery of thorium and rare earth from radioactive waste residue by functionalized ionic liquids

Thorium (Th) containing radioactive waste generated by ion-adsorbed rare earth ore (IATREO) separation plants poses a threat to the environment. The waste residue contains a much higher content of rare earth (RE) than the original IATREO. This study describes novel ionic liquids (ILs) containing cationic functionalization and evaluates their effectiveness in recovering Th and RE from the waste residue leaching solution (WRLS). Di-functionalization of the cation in ILs is more advantageous than mono-functionalization and non-functionalization, providing more coordination sites and achieving higher extraction and separation performance. In the simulated solution at an initial pH of 3, [OB2DTA][CA12] is able to extract 99.0% of Th and only 0.4% of RE, the Th/RE separation factor reaches 22114. The extraction reaction is carried out by an ion association mechanism. After 5 cycles of extraction-stripping-regeneration, the extraction and separation abilities of ILs remain stable. For the HCl leaching solution of waste residue, 99.5% of Th is separated in two extraction stages, while the total loss of RE is only about 15 mg/L. The recyclable separation strategy based on ILs simplifies the separation process of Th and RE, reduces chemical consumption, and provides a new idea for the treatment of IATREO waste residue.