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 Nd₂Fe₁₄BH_x and Nd(OH)₃ phases. At 200°C, Nd(OH)₃ was reduced without degradation of the magnetic Nd₂Fe₁₄BH_x 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.