Applying basic research on a dialkylphosphoric acid based task-specific ionic liquid for the solvent extraction and membrane separation of yttrium

Abstract

Satisfactory extractant for the separation of yttrium (Y) from other heavy rare earth elements (HREEs) in dilute solutions has not been reported for the time being. In this article, diethylhexyl phosphinic acid (P227) with lower pKa value, equilibrium and stripping acidity due to the absence of alkyl oxygen atoms, were incorporated into task-specific ionic liquids (TSILs) to realize the separation of Y. The synthesized [methyltrioctylammonium][di-(2-ethylhexyl) phosphinate] ([A336][P227]) were applied in both solvent extraction and membrane separation processes. Extraction and stripping of HREEs in both hydrochloric and nitric media were studied. A further understanding on the thermodynamics coordination mechanism with rare earths and acid was discussed. Separation factors implied it more suitable for the separation of Y in nitric medium. In addition, from the view of more sustainable and efficient application, polymer inclusion membrane (PIM) was fabricated. Membrane transport was demonstrated from the view of saving reagent and energy. Surface structure and composition analysis were characterized and transport experiments were conducted to verify the separation of Y. Stability and reusability of the PIM were proved well. All these provided the separation of Y from HREEs with a promising novel extractant and membrane separation technology.