Recovery of Sm(III), Co(II) and Cu(II) from waste SmCo magnet by ionic liquid-based selective precipitation process

Recovery of secondary resources including waste SmCo magnets contributes to easing the natural resources and environmental issues. For the development of recovery technologies, an ionic liquid (IL)-based precipitation route based on [trihexyl(tetradecyl)phosphonium]₂[benzene-1,4-dioxydiacetate] ([P_6,6,6,14]₂[BDOAC]) is presented. The slow release of [BDOAC]^2- from [P_6,6,6,14]₂[BDOAC] increases the kinetics difference in the formations of precipitates, and makes the precipitates contain less impurity. While cobalt-rich solution is obtained with no loss, precipitation efficiency of Sm(III) and Cu(II) reaches 96.8% and 100% respectively. Afterwards, Cu(II) is removed using aqueous ammonia and pure Cu(II) (96.4% precipitation efficiency) is obtained by adjusting the pH of cuprammonium complex solution. The proposed process without volatile diluent reveals higher separation factors of Sm/Co, Cu/Co and Sm/Cu. Lower acidities are efficient for the complete stripping of Sm(III) and Cu(II) from their precipitates. SmCl₃ and CuCl₂ solutions are obtained both with the high purities. Moreover, the IL-based precipitant can be regenerative. It is shown that the strategy is efficient for recovering and separating Sm, Co and Cu from the simulated leaching solution of waste SmCo magnets.