Recycling rare earth from ultrafine NdFeB waste by capturing fluorine ions in wastewater and preparing them into nano-scale neodynium oxyfluoride

Ultrafine NdFeB waste is a relatively clean waste produced during NdFeB magnet processing. Fluorine-containing wastewater is a common type of industrial wastewater, such as stainless steel pickling wastewater. In this work, rare earth element neodynium was recycled from ultrafine NdFeB waste by capturing fluorine ions in the fluorine-containing wastewater and prepared into neodynium oxyfluoride. The reaction process was investigated through UV-Vis-NIR, thermogravimetry/differential thermogravimetry (TG/DTG), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The neodymium hydroxide in the ultrafine NdFeB waste reacted with fluorine ions to form Nd(OH)2F, and Nd(OH)2F was then transformed into neodymium oxyfluoride after decomposition. The formed neodymium oxyfluoride is found to be particles with rhombohedral structure and a particle size of around 50 nm. The reaction kinetics of forming Nd(OH)2F was investigated. The reaction kinetic equation was established and the reaction activation energy was calculated. The effect of fluorine ion concentration on the reaction rate and products was evaluated. The results show that the reaction rate increases with the increase of fluorine ion concentration in the range of 0.01–1.5 mol/L, but it has little effect. In addition, the fluorine ion concentration affects the crystallinity of formed neodymium oxyfluoride. The recycling process not only realizes the sustainable utilization of rare earths, but also reduces the concentration of fluorine ions in the fluorine-containing wastewater, achieving two goals with one stone.