Selective hydrometallurgical processing of NdFeB magnets: impact of roasting on leaching selectivity and impurity dissolution

This study addresses the hydrometallurgical recycling of NdFeB magnets obtained from discarded hard disk drives. Magnet powders processed via hydrogen decrepitation were thermally oxidized at 850 °C to convert iron into insoluble oxides, minimizing iron dissolution during subsequent acid leaching. The research examined various parameters and different inorganic and organic acids – acetic, citric, trichloroacetic, methanesulfonic, and hydrochloric acids – to identify suitable operating conditions for rare-earth elements (. REE) recovery. Thermal pretreatment substantially improved iron selectivity but initially limited REE extraction. Elevated temperatures notably enhanced leaching performance since hydrochloric acid (HCl) at 93 °C achieved complete dissolution of REEs with minimal iron contamination. Effective leaching conditions (0.5 mol/L HCl, solid-to-liquid ratio S/L = 100 g/L, 93 °C, 8 h) were established, yielding high-purity solutions suitable for selective extraction. In addition to REEs, the dissolution behavior of other potentially valuable elements such as boron, cobalt, aluminum, and copper was also assessed, providing insights into their co-recovery potential. The resulting leachate composition, characterized by high REE concentrations and limited impurity levels, offers favorable conditions for implementing solvent extraction processes for the selective recovery of both REE and the other critical metals contained in the leachate. • Thermal oxidation at 850 °C suppresses iron dissolution during leaching. • Acid strength strongly influences REE recovery from roasted NdFeB powders. • HCl at 93 °C enables complete REE dissolution with minimal Fe contamination. • Co-dissolution of Al and B impacts downstream selective separation steps. • Optimized leaching yields high-purity REE solutions for solvent extraction.