A hydrothermal process for recycling SmCo5 permanent magnets

Sintered (Sm,Pr)Co 5 magnets were recycled by an environmentally-friendly hydrothermal process in a closed reactor under autogenous pressure. The hydrothermal treatment leads to the complete pulverization of the sintered magnets. The powders obtained after treatment consist in a mixture of non-magnetic particles and magnetic particles, which can be magnetically separated. The non-magnetic particles, which contain (Sm,Pr)(OH) 3 and (Sm,Pr) 2 O 3 phases, result from the reaction with water of the intergranular (Sm,Pr)-rich regions of the initial magnet. The magnetic particles, which contain a mixture of the (Sm,Pr)Co 5 , (Sm,Pr)(OH) 3 , (Sm,Pr) 2 O 3 and Co phases, correspond to the initial hard magnetic (Sm,Pr)Co 5 grains of the initial magnet, that have been dissociated during the hydrothermal treatment. Such a degradation of the hard magnetic phase can be reduced for short treatment times. The pulverization of the initial magnet without degradation of the hard magnetic phase could allow the production of hard magnetic particles to obtain new magnets. • An environmentally friendly hydrothermal process, in a closed reactor under autogenous pressure, was applied to SmCo 5 permanent magnets. • For short processing times, the magnets are fully pulverized into a mixture of SmCo 5 phase with Sm oxides and hydroxides. • For long processing times, the SmCo5 phase degrades into Sm oxides and hydroxides, and Co. • The pulverization of the initial magnet without degradation of the hard magnetic phase could enable the production of hard magnetic particles for the manufacture of new magnets.