Energy-efficient isobaric hydrothermal conversion of REEs in NdFeB waste magnets

Abstract

Waste magnets contain about 30 wt.% rare earth elements (REEs), yet less than 1 % are recycled, with most ending up in landfills, causing environmental harm. A hydrothermal process (HTP) was developed to convert end-of-life NdFeB magnets into REE hydroxides, iron (II, III) oxide, and hydrogen. This process uses hydrothermal reactions to pulverize crushed magnets into fine powder, eliminating the need for energy-intensive milling and oxidation prior to REE purification. Catalyst type, concentration, temperature, and magnet loading were optimized for an isothermal method. The results showed that 5 mM potassium sulfate at 275 °C were optimal for HTP. A more efficient isobaric process was then developed to improve reaction rates, yields, productivity, and safety. The isobaric process achieved 98 % yield in 24 hours, compared to 95 % yield in 36 hours for isothermal HTP. The isobaric process could also generate sufficient hydrogen to power the HTP.