Recycling of NdFeB magnets using nitration, calcination and water leaching for REE recovery

Abstract

NdFeB magnets currently dominate the magnet market. Supply risks of certain rare earth elements (REE), e.g. Nd and Dy, demand efficient recycling options that are applicable to different types and compositions with minimum use of chemicals and energy and with minimum waste generation. In this study, a combined pyro- and hydrometallurgical method is presented that is adjustable to all NdFeB magnets regardless of their composition. After completely transforming powdered samples into a metal nitrate mixture at room temperature for 1h, a low-temperature (e.g. 200°C) calcination and water leaching treatment resulted in 95–100% extraction efficiencies for Nd, Dy, Pr and Gd. The major impurity Fe (63.9wt.%) almost completely remained in the resultant residue (e.g. <1% extraction) forming a mixture of hematite and goethite as a useful by-product for related iron industries. Al and Co, representing minor impurities with individually <2wt.%, also mostly remained in the residue (i.e. <40% extraction), thereby enabling the production of a liquid with very high REE purity. Such a solution then can be directly treated with subsequent shortened downstream processes without pre-treatments required for impurity removal. Due to decomposition reactions of impurities (including Fe) during the low-temperature calcination stage (e.g. 200°C), the majority of consumed acid (i.e. the only chemical used) is recyclable resulting in a potentially environmentally-friendly and cost-effective flowsheet.