Highly efficient and selective recovery of rare earths from NdFeB waste via water-regulated deep eutectic solvent

A water-regulated DES strategy was developed for recovery NdFeB scrap. • REEs and Fe are directly separated and recycled in ChCl-OA-H 2 O DES. • REE recovery reached 97% at a solid/liquid ratio of 100 g L −1 . • Even after 10 cycles, the recycling efficiency of DES remains above 90%. • Purity of REE oxalate and FeC 2 O 4 ·2H 2 O respectively exceeds 98.8% and 97.5%. The efficient recycling of rare earth elements (REEs) from waste neodymium-iron-boron (NdFeB) magnets is critical for supply chain security and environmental sustainability. However, conventional recycling methods face significant challenges due to complex separation procedures, excessive reagent consumption, and the generation of substantial quantities of secondary waste. This study develops an efficient and green process for the sequential recovery of high-purity mixed REEs (primarily Nd, Pr, Ce) and iron (Fe) from waste NdFeB magnets, utilizing a water-regulated choline chloride-oxalic acid (ChCl-OA-H 2 O) deep eutectic solvent (DES). After calcination pretreatment selectively converts the NdFeB alloy into soluble REE 2 O 3 and Fe 2 O 3 , Response surface methodology (RSM) was employed to optimize the leaching process. Under the identified optimized conditions (water content: 39.56%, solid/liquid ratio: 98.15 g/L, temperature: 91.06°C, time: 12.07 h), leaching efficiencies reached 97.81% for Nd and 99.23% for Fe. The DES system demonstrated excellent recyclability, maintaining >90% Nd recovery over ten cycles without significant performance loss. Mechanistic studies indicate that ChCl-OA has the dual functionality: selective precipitation of REE 3+ as insoluble oxalates REE 2 (C 2 O 4 ) 3 ·10H 2 O, and complexation of Fe 3+ as soluble [Fe(C 2 O 4 ) 3 ] 3- . The dissolved [Fe(C 2 O 4 ) 3 ] 3- is subsequently recovered from the filtrate as high-purity FeC 2 O 4 ·2H 2 O (97.52%) via UV-Vis photoreduction. Besides, water addition strategically reduces DES viscosity, overcoming the mass transfer limitations that plague conventional DES systems. This work establishes a sustainable, closed-loop pathway for the comprehensive valorization of NdFeB waste, directly addressing the critical trade-off between recovery efficiency and environmental impact in rare earth recycling. Download: Download high-res image (328KB) Download: Download full-size image