Aeration leaching for sustainable recovery of rare earth elements from spent NdFeB magnets

Efficient and selective recovery of rare earth elements (REE) from NdFeB magnet waste remains challenging due to co-dissolution of iron in conventional hydrometallurgical processes. In this study, an aeration-assisted FeCl₂·4H₂O leaching system was developed to achieve selective REE dissolution with in-situ iron removal. The effects of lixiviant, lixiviant concentration, temperature, particle size, and solid-to-liquid (S/L) ratio were systematically investigated. Under optimized conditions (10% excess FeCl₂·4H₂O, 70 °C, S/L = 1:20, particle size <88 μm), ~99.1% REE dissolution was achieved within 4 h, while iron dissolution was suppressed to ~0.14%. Temperature and S/L ratio significantly influenced dissolution efficiency, with REE recovery improving from ~90.4% at room temperature to ~99.1% at 80 °C, and from ~77.5% (S/L 1:10) to ~99.1% (S/L 1:20). A comparison of lixiviants revealed superior performance of chloride systems. FeCl₂·4H₂O and HCl achieved ~99.1% and ~98.8% REE recovery, respectively, whereas sulphate-based systems (FeSO₄.7H₂O and H₂SO₄) showed lower efficiencies of ~89.5% and ~90.7%. Chloride media exhibited more favorable pH and redox evolution, leading to enhanced selectivity and lower residual iron. Characterization confirmed that iron was converted into oxyhydroxide phases, predominantly γ-FeOOH, while REE selectively dissolved in solution. The recovered REE were precipitated as oxalates and converted to high-purity oxides after calcination. The study demonstrates a simple and efficient route for selective REE recovery via aeration leaching, offering strong potential for sustainable NdFeB recycling.