P350-N235 synergistic extraction system used for the recovery of Nd(III) from waste NdFeB magnets

Abstract

The recovery of Nd(III) from NdFeB permanent magnets is gaining increasing attention. In the rare earth elements separation industry, wastewater produced through saponification has become a serious environmental problem. In this work, a novel non-saponification P350-N235 synergistic extraction system was established for the extraction of Nd(III) from nitric acid medium. Almost 100% of Nd(III) was extracted by using a P350-N235 system when the molar fraction (X) of P350 was 0.3. And the synergistic enhancement factor Rmax reached 60.03. Firstly, the effects of time, pH, volume ratio and other variables were investigated to determine the extraction behaviors. Response surface methodology (RSM) was used to optimize the extraction conditions. The mechanism of synergistic extraction was investigated by FT-IR, UV–vis, NMR methods and ESP maps, indicating that the composition of the extracted complex was Nd(NO3)3·(P350)2.5(N235)2.5. Then, the extraction thermodynamics and kinetics were also thoroughly investigated, the extraction process is demonstrated to be a spontaneously exothermic reaction. In the NdFeB leaching solution, the synergistic system showed excellent separation factor (β) for Nd/Sm (1.43), Nd/Gd (7.33), and Nd/Dy (9.81). Finally, after 5 cycles, the P350-N235 synergistic system maintained high extraction efficiency. In conclusion, this study overcame the saponification problem in traditional extraction techniques and proposed an environmentally friendly green extraction system.