Recovery of Rare Earth Elements from NdFeB Magnet by VIM-HMS Method

Abstract

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.

Electrochemical Recovery of Rare Earth Elements from Magnets: Conversion of Rare Earth Based Metals into Rare Earth Fluorides in Molten Salts

“…The formed rare earth uoride can subsequently be processed in the same reactor through an electrolysis route so that RE can be deposited as a cathode product. The results of XRD and EPMA analysis of the reacted samples indicate that AlF 3 , ZnF 2 and FeF 3 can act as strong uorinating agents for extraction of rare earth from NdFeB magnet, converting the RE to REF 3 .The results con rm the feasibility of the rare earth metals recovery from scrap NdFeB magnet as raw material. The uoride conversion-electrolysis route suggested in the present work enables the extraction of rare earth metals in a single step using the above-mentioned uxes.…”

“…An effective process for the recycling of rare earth scrap is a major concern since most developed countries import their required rare earth elements 2) . Hydrometallurgical and pyro-metallurgical process routes have been the subject of investigation by a number of researchers [3][4][5][6][7] . However, the drawbacks of hydrometallurgy processes are the low reaction rates and the serious environmental problems arising from the huge amounts of waste water generated in the process, which, in turn, need further processing.…”

“…A new approach involving molten uoride bath has been proposed in a recent study at TU Delft for solving the problem of low solubility and oxy uoride formation of rare earth oxides (REOs) in molten uorides. In this approach, AlF 3 , ZnF 2 , FeF 3 and Na 3 AlF 6 were used as uorinating agents in the LiF-Nd 2 O 3 system. The rare earth oxide was converted into rare earth uoride, which can subsequently be processed in the electrolysis route in which rare earth metal is electrochemically extracted as the deposition on the cathode.…”

“…Complete conversion of REO in molten uorides can overcome the problem of the low solubility of REOs in the molten uorides. The objective of the present work is to examine the applicability of this process concept for the extraction of neodymium and other rare earth elements from NdFeB magnets, using AlF 3 , ZnF 2 , FeF 3 and Na 3 AlF 6 in the LiF-NdFeB system. It is interesting to examine the possibility of selective extraction of the rare earth metal from Nd magnet by uorination.…”

“…The formed rare earth uoride can subsequently be processed in the same reactor through an electrolysis route so that RE can be deposited as a cathode product. The results of XRD and EPMA analysis of the reacted samples indicate that AlF 3 , ZnF 2 and FeF 3 can act as strong uorinating agents for extraction of rare earth from NdFeB magnet, converting the RE to REF 3 .…”