Efficient and Sustainable Regeneration of Bifunctional Ionic Liquid for Rare Earth Separation

Abstract

An effective and sustainable strategy of regeneration is important for the industrial application of functionalized ionic liquid in hydrometallurgy. The transformations of [tri-<i>n</i>-octylmethyl­ammonium]­[bis-sec-octylphenoxyl acetate] ([N₁₈₈₈]­[SOPAA]) and [trihexyl (tetradecyl) phosphonium]­[sec-octylphenoxy acetate] ([P_6,6,6,14]­[SOPAA]) under acidic and alkaline conditions were investigated. This paper developed a novel approach for sustainable stripping and efficient regeneration of acid–base coupling bifunctional ionic liquid (ABC-BIL) for rare earth element (REE) separation. After the stripping using deionized water, both NaOH and Na₂C₂O₄ were indicated to be effective for the regeneration of organic phase containing [N₁₈₈₈]­[SOPAA]. In order to recycle REE, the precipitates of REE­(OH)₃ and REE₂(C₂O₄)₃ were analyzed, and a sedimentation–calcination strategy was proposed. The investigation of sedimentation–calcination also offered a promising method for the preparation of REE nanomaterial