Recycling of Nd−Fe−B sintered magnets into a single phase by solvothermal treatment and CaH2 reduction-diffusion

Abstract

Recycling computer hard disk drives from Waste Electrical and Electronic Equipment (WEEE) has been achieved according to a two-step approach that combines solvothermal treatment and CaH2 reduction-diffusion, resulting in the production of a single-phase material. The magnets underwent solvothermal treatment, followed by CaH2 reduction at varying temperatures (200°C, 250°C and 300°C). We examined the impact of CaH2 as a reducing agent on the final product, using X-ray diffraction, Mössbauer spectrometry and SQUID magnetometry. After the solvothermal treatment, the powder contains both Nd2Fe14BHx and Nd(OH)3 phases. At 200°C, Nd(OH)3 was reduced without degradation of the magnetic Nd2Fe14BHx phase, as confirmed by Mössbauer spectrometry. Furthermore, an analysis of the magnetic properties indicates an increase in magnetization after CaO removal, confirming its successful elimination.