A Novel Short Process for the Preparation of High-Purity Iron Phosphate from the Iron Tailings of NdFeB Waste

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The continuously accumulated NdFeB waste has become a critical secondary resource for recycling rare earth elements (REEs). However, there is a lack of effective disposal methods for the iron-rich tailings generated after REE extraction, which not only imposes severe environmental pressure but also leads to a significant loss of iron resources. This study proposes an innovative, economical, environmentally friendly, and short process for the direct synthesis of high-purity FePO4·2H2O from NdFeB waste-derived iron tailings. Using phosphoric acid as both a leaching agent and a phosphorus source, the iron in the tailings was dissolved and directly converted into FePO4·2H2O without the need for pH adjustment or additional reagents. Under the optimized conditions (3 mol/L H3PO4, 95 °C, 180 min, and a liquid-to-solid ratio of 10), FePO4·2H2O was obtained with >99% purity and had phosphorus and iron contents of 16.63% and 29.55%, respectively, and a P/Fe molar ratio of 1.01, meeting the industrial standard for battery-grade FePO4·2H2O (HG/T). The subsequent calcination of FePO4·2H2O at 600 °C for 2 h yielded anhydrous FePO4. The initial specific discharge capacity of the LiFePO4/C (LFP/C) cathode prepared from anhydrous FePO4 reached 144.8 mAh/g. After 150 cycles, the capacity retention rate remained at 98.47%. The innovative process developed in this study enables the recovery and high-value utilization of iron from the iron tailings of NdFeB waste, eliminating secondary pollution while significantly streamlining the process. This work is expected to advance the sustainable recycling of NdFeB waste and contribute to the establishment of a closed-loop and environmentally friendly industrial recycling system for spent magnets.