Hydrometallurgical processes for recycling of SmCo magnets: A comprehensive review

Samarium-cobalt (SmCo) permanent magnets play a critical role in high-performance applications in various industries due to their superior thermal stability and resistance to corrosion. Although they represent a smaller market share than other rare earth magnets, their utility in extreme thermal environments (∼300 °C) makes their recycling imperative, especially given the limited availability of samarium and cobalt. The brittle nature of SmCo magnets generates substantial waste during manufacturing, underscoring the need for efficient recycling strategies. Among recovery technologies, hydrometallurgy is one of the most efficient and widely investigated routes, offering high recovery rates through well-established leaching and separation techniques. This review comprehensively examines the key steps in recycling SmCo magnets, evaluating various options at each stage while highlighting their efficiencies, challenges, and limitations. Recycling involves pretreatment steps, such as demagnetization and size reduction, to enhance leaching efficiency. Inorganic acids (HCl, H 2 SO 4 , and HNO 3 ) enable greater than 99% Sm and up to 90% Co recovery, although challenges such as Sm precipitation can be encountered. Greener alternatives using organic acids with H 2 O 2 offer a lower recovery rate (∼85%) while reducing environmental impact. Post-leaching separation steps, including solvent extraction (SX), ionic liquids (ILs), deep eutectic solvents (DESs), and ion exchange (IX), offer high selectivity for SmCo recycling. Stripping with oxalic or mineral acids enables greater than 97% Sm recovery. Electrochemical methods, utilizing intact magnets as anodes in non-aqueous systems, would yield an efficiency of over 85% while minimizing waste and acid usage. Despite encouraging progress, numerous research gaps remain. By consolidating current knowledge and emerging trends, this assessment identified critical technical challenges, mentioned existing openings, and outlined clear research directions to advance the development and broader adoption of hydrometallurgical routes for SmCo magnet recycling.