Efficient separation for yttrium and heavy rare earth elements using functionalized quaternary ammonium ionic liquids

Abstract

Given the similar ionic radii of heavy rare earth elements (HREEs), sixteen functionalized ionic liquids (FILs) with potential extraction and separation properties were designed and prepared, also their feasibilities for yttrium (Y) separation from HREEs were evaluated. The results show that [N16MOP][HDA] is the optimal extractant for Y separation from other HREEs, achieving a Ho/Y separation factor of 2.82. The extraction reaction is based on an ion pair mechanism, where a HoCl3 molecule is extracted by two [N16MOP][HDA] molecules. Complete stripping of the loaded rare earth elements (REEs) can be achieved using 0.1 mol/L hydrochloric acid. Deionized water is used as a scrubbing agent, the average separation coefficient between Y and other HREEs during the scrubbing process is 2.5. After six cycles of continuous operation for 15 h, the organic phase maintains stable extraction and separation capabilities, demonstrating good recyclability and periodic stability. This study introduces a sustainable method for separating Y from HREEs using novel FILs, which is more efficient and consumes fewer chemical reagents. The results of this study indicate that the introduction of functionalized cation in FIL enhances the affinity and selectivity of HREEs. This provides valuable insights into the design of FIL-based extractents and their potential applications in sustainable rare earth separation.