Recovery of mixed rare earth oxide and fine powder of metallic iron from spent NdFeB magnet of wind turbines

Abstract

NdFeB magnet is used in various application such as generators, electric vehicles, hard disc, rare earth roll magnetic separator etc. due to its excellent magnetic properties. Currently, ~26% of rare earths produced worldwide are used for the production of NdFeB magnet, but less than 1% of the rare earths are recycled after completing their life cycle. Due to continuous increase in demand of rare earths and scarcity of their primary resources, end-of-life NdFeB magnet emanated as potential source of rare earths. Therefore, now-a-days research is primarily focused on the utilization of waste NdFeB magnets for recycling and recovery of valuables metals in the usable form. Investigation has been carried out to separate rare earth oxide and metallic Fe directly by magnetic separation after selective oxidation of rare earths in NdFeB magnet. But the magnetic separation is ineffective due to partial oxidation of iron. In the present study, the rare earths are recovered selectively during leaching from the roasted NdFeB magnet powder and the leach residue of iron oxide is utilized to produce fine powder of metallic iron. Mixed oxide of rare earths of 99% purity is obtained from the rare earth rich leach liquor. The reduction of the leach residues has been studied using waste graphite of spent electrodes of arc furnace as reductant, in horizontal tubular furnace at different temperature and for various time period. It is found that 93% of iron oxide reduces to fine powder of metallic iron. The fine powder obtained after reduction, has been characterized by XRD which confirm the conversion of iron oxide to metallic iron phase. Thus, the present investigation highlights the recovery of mixed rare earth oxide and fine powder of metallic iron obtained as valuables from waste NdFeB magnet, which can be utilized directly as raw material for the production of fresh magnet.