Samarium-cobalt (Sm-Co) permanent magnets are widely used in high-temperature, high-performance applications, but their recycling is difficult due to their thermal stability and complex alloy chemistry. However, the strategic and economic importance of Sm and Co makes the development of efficient recycling routes increasingly critical. This review focuses on pyrometallurgical approaches for recovering Sm and Co from end-of-life magnets and industrial scrap. Thermal pretreatment, such as demagnetization near or above the Curie temperature (∼720-820 °C), not only removes magnetic properties but also promotes surface oxidation, producing more reactive oxide phases that facilitate subsequent processing. Among pure thermal routes, vacuum distillation exploits differences in vapor pressure to selectively evaporate Sm under reduced pressure. Recovery efficiency and final purity depend strongly on precise temperature control and the choice of condenser material. Molten salt extraction in LiCl-KCl eutectics uses oxygen sparging to convert SmCl 3 into SmOCl while leaving Co in the melt, enabling phase separation. The glass slag technique with molten B 2 O 3 transfers Sm into the slag as Sm 2 O 3 /SmBO 3 and yields Co or Fe-rich alloys with very low Sm content. Hybrid pyro-hydrometallurgical methods, notably nitric acid baking followed by controlled thermal decomposition, exploit the differing thermal stabilities of Sm, Co, and Fe nitrates to selectively dissolve Sm while converting base metals to insoluble oxides. Sulfation and selective oxidation are additional thermal steps that can improve phase separation prior to aqueous recovery. Moreover, solid-state chlorination showed a higher reactivity of Sm toward HCl (with Co being less reactive) under optimal conditions. Drawing together the latest findings and emerging trends, this review highlights the key technical challenges, critical knowledge gaps, and promising opportunities. This work examined the feasibility of all reported chemical reactions and assessed them using Gibbs energy. It also sets out focused research priorities to accelerate the development and wider adoption of pyrometallurgical strategies for Sm-Co magnet recycling. Particular emphasis is placed on energy-efficient demagnetization and volatilization, impurity-tolerant molten salt and slag chemistries, durable condenser materials, emissions control, and practical integration with hydrometallurgical steps.
Gharavi et al. (Fri,) studied this question.