Flow-driven enhancement of neodymium and dysprosium separation from aqueous solutions

Abstract

Selective extraction of rare earth elements (REEs) from waste NdFeB magnets and natural mineral sources has been challenging due to the similar properties of neodymium (Nd) and dysprosium (Dy). Current separation methods mainly include solvent extraction and organic ligand-based selective precipitation, which are chemical- and energy-intensive in addition to the long separation times required to reach thermodynamic equilibrium. Here, we demonstrate a laminar co-flow method that relies on flow-induced non-equilibrium conditions to selectively precipitate Dy³⁺ from aqueous solutions containing mixed Nd³⁺ and Dy³⁺ at various ratios. The concentration of reactant sodium dibutyl phosphate for selective precipitation was identified based on the differences in the spatiotemporal dynamics of the Nd³⁺ and Dy³⁺ precipitates. Under optimized conditions, our method showed increased Dy purity in the precipitate product at significantly shorter reaction times, compared to commonly used convective bulk mixing. We found a nearly Dy-pure (99.9%) precipitate from starting mixtures of Nd : Dy in 50 : 50 and 30 : 70 ratios. Our single-step method is efficient and environmentally friendly and does not require harmful organic solvents or difficult to synthesize complex ligands.