Separation and Recovery of Fe and REEs from a Hydrochloric Acid Leachate of NdFeB Waste Using Aliquat 336-Based Solvent Extraction

Neodymium–iron–boron (NdFeB) waste represents a valuable secondary source of rare earth elements (REEs). However, existing recovery technologies face several challenges, such as the difficulty of selectively recovering REEs, the generation of large volumes of secondary iron-rich slag, and an overall low level of comprehensive resource utilization. In this study, Aliquat 336 was applied for the selective extraction and separation of REEs and iron (Fe) from hydrochloric acid leachate derived from NdFeB waste. Experimental results showed that under optimized conditions—specifically, a 15% Aliquat 336 concentration, an organic-to-aqueous phase ratio of 1:2, and a 2 min extraction time—Fe extraction efficiency reached 99.93% after three-stage countercurrent extraction, while REEs were predominantly retained in the aqueous phase. Subsequent oxalic acid precipitation of the raffinate yielded RE2(C2O4)3·10H2O with a purity of 99.60%. Moreover, under stripping conditions of 2 mol/L NaOH, a phase ratio of 2:1 (aqueous to organic), and a 2 min contact time, over 99.21% of Fe was stripped after three-stage countercurrent stripping, resulting in Fe(OH)3 with a purity of 99.26%. The extraction mechanism followed an anion-exchange process: under high chloride ion concentrations, Fe3+ formed anionic FeCl4− complexes, which were exchanged with Cl− ions in Aliquat 336 and transferred into the organic phase, whereas RE3+ cations remained in the aqueous phase, enabling efficient separation of Fe and REEs. These findings provide important insights for improving the comprehensive utilization of NdFeB waste and promoting the green and sustainable development of secondary rare earth resource recycling.