Study on phase transformation behavior of NdFeB waste before and after leaching

In order to study the process mineralogy of NdFeB waste before and after leaching, it was roasted at 650 ℃ for 2 h, and then leached with 4 mol/L hydrochloric acid to obtain leaching residues. The calcination products and leaching residues were characterized by XRF, XRD, XPS and SEM-EDS. The experimental results showed that the calcined products were mainly composed of Fe₂O₃, Fe₃O₄, SiO₂, NdFeO₃ and Nd₂O₃, and the content of rare earth in these products was 16.40%. After leaching, there was no NdFeO₃ and Nd₂O₃ in the residues, and the content of rare earth was only 0.66%. In XPS detection, Fe existed in the roasting products in two valence states of Fe(Ⅱ) and Fe(Ⅲ), indicating that Fe was not completely oxidized into Fe(Ⅲ) at this temperature, and there was still some Fe(Ⅱ). Fe(Ⅱ) was also detected in the slag besides Fe(Ⅲ), indicating that Fe(Ⅱ) was not completely removed in the leaching process. This experiment further improves the leaching theory of NdFeB waste and is quite useful for guiding the recovery of NdFeB in the future.