Selective recovery of rare earth elements from NdFeB magnet waste via deep eutectic solvents: Process optimization and DFT insights
Jaishree Yadav, Shuronjit Kumar Sarker, Warren J. Bruckard, Veeriah Jegatheesan, Nawshad Haque, Biplob Kumar Pramanik
Abstract
Recycling electronic waste, such as NdFeB magnets, offers a sustainable solution to address the supply chain challenges of rare earth elements (REEs). The objective of this study was to (i) develop and optimize a non-corrosive, efficient deep eutectic solvent (DES)-based leaching process for NdFeB magnet waste and (ii) selectively extract Nd from NdFeB magnet to make a high-purity Nd oxide product. The influence of pretreatment on leaching efficiency was systematically examined. Selective REEs leaching was achieved from NaOH-digested and roasted material using 1:1 ratio of choline chloride to malonic acid. This DES exhibited the highest selectivity, with 95.5 % Nd leaching, 92 % Pr leaching and only 1.1 % Fe leaching at 80 °C and a solid-to-liquid ratio of 1:20 over 6 h. The leached Nd 2 O 3 was extracted from the DES through stripping with oxalic acid, followed by oxidative roasting, achieving a purity of >99.5 % suitable for NdFeB magnet production. Additionally, Density Functional Theory calculations indicated that the interaction between choline chloride and malonic acid results in a 35.37 eV decrease in energy, highlighting the formation of hydrogen bonds and the synthesis of DES. This process offers a highly efficient, environmentally sustainable method for recovering REEs from magnet waste, making it a promising approach for future industrial applications.