Highly efficient and selective separation of dysprosium and neodymium from polyethylene glycol 200 solution by non-aqueous solvent extraction with P350

Abstract

Recycling of Nd(III) and Dy(III) from waste NdFeB magnets is increasingly critical in the sustainable development of rare-earth elements (REEs) industry. The efficient separation of Nd(III) and Dy(III) from conventional aqueous solution by solvent extraction (SX) is facing huge challenge due to the high activity, high interfacial tension and the high dielectric constants of water that affect the coordination of REEs with the extractant. Herein, a novel non-aqueous solvent extraction (NASX) system based on neutral extractant P350 was developed to extract Nd(III) and Dy(III) with high extraction efficiency and separation factor. In this extraction system, the majority of water in the aqueous phase was replaced by different low-dielectric-constant polar molecular organic solvents (PMOSs) to reduce the influence of water during extraction. The effect of the type and content of PMOSs, P350 concentration, extract equilibration time and temperature on the separation performance were systematically investigated. It was encouraging to find that the favorable separation factor of Nd(III) and Dy(III) elements (βNd/Dy) was determined to be 201 when extracted from 70 vol% PEG 200 with 0.2 mol/L P350, which was higher than that in traditional extraction from aqueous phase. Slope analysis method was used to determine the extractant stoichiometry and the main species of extraction complex was identified as DyCl3·2L which was verified by Fourier infrared spectroscopy (FT-IR). Furthermore, in the simulation of recovery of NdFeB magnetic immersion solution experiment, the extraction efficiency (E%) of Dy(III) can reach 85 %, while co-extraction of Nd(III) was only 6 % and the βDy/Nd was as high as 83.4. According to the McCabe-Thiele diagram, 3-stages counter-current solvent extraction was needed to completely extract Dy(III). Moreover, 97.11 % of Nd(III) and 98.5 % of Dy(III) in the loaded organic phase can be sequentially stripped by 0.04 mol/L and 0.4 mol/L HCl, respectively. These results indicated that the developed processes in this work have superior extraction efficiency, large separation factors and excellent stripping stability. Eventually, a P350-PEG 200 extraction system-based separation process was proposed in the hope of providing a novel and low-cost alternative to the efficient recycle of Nd(III) and Dy(III) from end-of-life NdFeB.