The spent neodymium–iron–boron (NdFeB) magnet is a highly valuable secondary resource of rare earth elements (REEs). Hydrometallurgical processes are widely used in recovering REEs from spent NdFeB magnets, but they will consume large amounts of organic chemicals, leading to severe environmental pollution. This work developed an alternative green route to selectively recover REEs from spent NdFeB permanent magnets using a purely inorganic zinc salt. The Hammett acidity measurement showed that concentrated ZnCl2 solutions could be regarded as a strong Brønsted acid. Concentrated ZnCl2 solutions achieved a high separation factor (>1 × 105) between neodymium and iron through simple dissolution of their corresponding oxide mixture. In the simulated recovery process of spent NdFeB magnets, the Nd2O3 product was successfully recovered with a purity close to 100% after selective leaching by ZnCl2 solution, sulfate double-salt precipitation, and oxalic acid precipitation. The separation performance of the ZnCl2 solution for Nd2O3 and Fe2O3 remained almost unchanged after four cycles. The energy consumption and chemical inputs of this process are about 1/10 and half of the traditional hydrometallurgy process separately. This work provides a promising approach for the green recovery of secondary REE resources.

The replacement of traditional solvents in lithium-ion battery recovery process by deep eutectic solvents (DESs) has been widely reported. This work proposed a DES modified by reducing agents for the efficient leaching of LiCoO2 (LCO) and lithium nickel cobalt manganese oxides (NCMs) to overcome the intractable difficulty of previous research (high viscosity, poor reuse performance, and operation conditions). The DES of guanidine hydrochloride (GUC) and lactic acid (LAC) with 1 wt % ascorbic acid could dissolve almost 100% of LCO and NCMs under a very mild condition at a solid–liquid ratio of 1:50. The maximum contents in GUC-LAC were 3188 ppm for Li and 19,045 ppm for Co. After stripping Co by oxalic acid and supplementing VC, GUC-LAC-VC could maintain the dissolution properties with at least three cycles. In addition, the acidity and reducibility were measured through Hammet acidity and cyclic voltammetry methods, as key factors for the dissolution of Li and Co.

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