Towards Sustainable Hydrometallurgy: Water Reuse and Iron Recovery from Effluents of REE Extraction from NdFeB Magnets

The NdFeB magnetic material is widely used in modern industry and electronics. Recycling spent magnets containing 30–40 wt.% Rare Earth Elements (REEs) and 60–70 wt.% iron is essential for resource recovery. This study focuses on treating wastewater from hydrometallurgical REE extraction to enable water reuse and iron recovery. Experiments investigated the influence of temperature (25–60 °C) and oxalic acid concentration (50–120% stoichiometric amount) on iron precipitation as the main focus. Optimal iron recovery of 85.3% and 86.8% was achieved at 25 °C using 80% and 100% stoichiometric oxalic acid, respectively. Simultaneously, praseodymium removal exceeded 94%. The Differential Scanning Calorimetry (DSC) analysis identified a peak between 168.8 °C and 245 °C, with the peak temperature recorded at 214.5 °C, indicating the optimal calcination temperature for iron oxalate. This was confirmed through oven testing and X-ray Diffraction (XRD) analysis. The treated effluent exhibited a Chemical Oxygen Demand (COD) of 418 mg/L, with residual Fe and Pr concentrations significantly reduced to 5.7 mg/L and 4.3 mg/L, respectively. This approach demonstrates an efficient method for wastewater treatment and resource valorization, promoting sustainability in the recycling sector.