Review and test on rare earths recovery from polishing powder waste

Rare earth polishing powder has gained widespread usage in the surface polishing of high-precision materials, exhibiting an annual growth rate exceeding 10 %. However, a significant portion of this powder is discarded due to impurities and the need for particle size refinement. The waste generated from polishing powder contains 10.31 %-86.93 % rare earth elements, making secondary recycling economically viable. This work critically analyses and verifies existing methods for recovering rare earths(REs)from rare earth polishing powder waste (REPPW). It concludes that the acid roasting, water leaching, and reduction, coordination acid-leaching methods can achieve rare earth recovery rates exceeding 98 %, offering a relatively simple and environmentally friendly process. We highlight various rare earth recovery processes from REPPW, including alkaline roasting with acid-leaching, acid roasting with water-leaching, acid-leaching with alkali dissolution and washing, and acid-leaching with the aid of reducing agents. It is found that the acid-leaching-water leaching process and the acid-leaching-reducing agent synergy process demonstrate high recovery rates, ease of operation, reduced environmental impact, and stable product quality. It is recommended that researchers focus on refining leaching theories, optimizing process conditions and determining key parameters to further advance the production of rare earth recovery from REPPW. The findings of this study contribute to the development of sustainable practices for the recovery of valuable REs from industrial waste streams.