The recovery of rare earth by a novel extraction and precipitation strategy using functional ionic liquids

A novel precipitation strategy grounded on [trihexyl(tetradecyl)phosphonium]2[4,4′-isopropylidenebis(phenoxyacetate)] (abbreviated as [P66614]2[IOPAA]) was put forward for rare earth element (REE) recovery. The H2IOPAA and [P66614]2[IOPAA] were synthesized and characterized by NMR, IR and elemental analysis. The factors in the precipitation process such as the equilibrium time, pH value of aqueous phase, concentration of salt-out agent and mole amount of IL were investigated. In addition, the precipitation mechanism of [P66614]2[IOPAA] for Pr(III) was proposed to be 2Praq3+ + 6Claq− + 3{[P66614]2[IOPAA]}IL = 6[P66614]ClIL + Pr2[IOPAA]3↓. The process was successfully tested for the recovery of REE from simulated leaching solution of Nd-Fe-B scrap. After removing the iron ion with [P66614]Cl, a high recovery rate (99.85%) of REE was obtained. Without saponification, organic diluent or oxalic acid, the proposed precipitation strategy has revealed the potential to be a sustainable process to the quantitatively recovery REE.