Sammendrag
A novel method to recover rare earth elements (REEs) from NdFeB magnets was developed. This method involves three basic steps, i.e., the vacuum induction melting (VIM) process, the hydrolysis process and the magnetic separation process (HMS). In the VIM process, the NdFeB magnets were melted in a graphite crucible under vacuum (<1 Pa), in which way the rare earth carbides formed by the reaction of REEs and carbon, and the carbon saturated NdFeBCsat alloy was obtained. On the basis of the hydrolysis of rare earth carbides, the REEs were separated from the NdFeBCsat alloy by the reaction of the rare earth carbides phase with water. Thus, the rare earth hydroxides and iron-based metal residues were produced. Magnetic separation was further used to remove the iron residues from the rare earth hydroxides. Through this method, the optimal recovery ratio reached 93%, and the purity of the rare earth hydroxides was as high as 99.7%. Along with the VIM-HMS process, the investigation of NdFeBCsat alloy, the morphology of the rare earth hydroxides and the conversion of rare earth hydroxides to rare earth oxides are also presented in this paper. In this research, the X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductive-coupled plasma spectroscopy (ICP), mass spectrum analyses, CS analyses, magnetic properties analyses and nitrogen physisorption analyses were applied.