Separation and coextraction of REEs and Fe from NdFeB sludge by co-leaching and stepwise precipitation

NdFeB sludge is a waste with high economic value. NdFeB waste recycling has the disadvantage that only rare earths are recycled, but iron (Fe) is not recycled, which results in large amounts of secondary solid waste. In this paper, a process flowchart of the co-extracted rare earth elements (REEs) and Fe by co-leaching and stepwise precipitation from NdFeB sludge was developed. The results show that after the NdFeB sludge was pretreated, co-leaching with hydrochloric acid, rare earth precipitation with oxalic acid, and Fe precipitation with reduction iron powder, 98.28% of the REEs were recovered in the form of RE2(C2O4)3·10H2O, and 94.65% of the Fe was recovered in the form of FeC2O4·2H2O. Due to the low solubility product constants of the rare earth oxalates, when oxalic acid was added to the leachate, the REEs precipitated rapidly, while Fe was still present as FeCl4–, Fe(C2O4)2–, and FeC2O4+ in the precipitated REEs solution. Therefore, the selective separation and precipitation of REEs and Fe was achieved. The process has the advantages of high comprehensive utilization of resources and no secondary solid waste or wastewater pollution.