Relationship between Nd-rich phase and oxygen content for additive-free sintering with regenerated powder from magnet sludge waste

Abstract

<jats:p>Recycling of Nd-Fe-B magnet sludge into high-performance powders is critical for sustainable rare-earth resource utilization. In this study, Nd-Fe-B powders were regenerated via a reduction-diffusion process and subjected to different washing treatments to investigate their effects on microstructure, phase composition, and magnetic properties. Conventional water washing at larger scales resulted in increased oxidation, depletion of Nd-rich phase, while requiring prolonged washing cycles and excessive water consumption. In contrast, scale up washing with an NH4NO3 solution in methanol effectively minimized oxidation, preserved Nd-rich, and maintained a uniform 1–2μm particle size distribution. The resulting powders exhibited superior magnetic properties, including high coercivity, enhanced squareness, and an improved maximum energy product. The NH4NO3 in MeOH washing method also demonstrated higher yield, improved processing efficiency, and scalability, highlighting its potential as a practical approach for sustainable production of regenerated Nd-Fe-B powders. These findings provide a promising pathway for recycling magnet sludge into high-quality powders suitable for sintered magnet fabrication, contributing to resource conservation and the advancement of rare-earth recycling technologies.</jats:p>