Selective recovery of rare earth elements from Nd-Fe-B magnet scrap by PVC pyrolysis

A large amount of Nd-Fe-B magnet scraps are generated during magnet manufacture process. Nd-Fe-B magnet scraps contain valuable rare earth elements which are limited and unevenly located in some particular countries. Therefore, recycling processes for the Nd-Fe-B magnet scraps are necessary for the resource stability. Selective chlorination of the rare earth elements by hydrogen chloride gas which obtained from the pyrolysis of polyvinyl chloride (PVC) was performed. In thermogravimetric analysis (TGA) instrument, non-isothermal experiment and isothermal experiments were carried out. Nd-Fe-B magnet scraps (4 g) and PVC powders (4 g) were mixed and compacted to pellets. Non-isothermal experiments were performed under heating rate 1 K/min. Also, the temperature and the PVC/magnet scrap ratio were varied in isothermal experiment. After the reaction, the products were leached in distilled water. Samples were analyzed by XRD, SEM, and ICP-OES. TG curves obtained from non-isothermal experiment showed sharp weight loss at about 573 K and 703 K, and it is attributed to the formation of HCl gas and polyene structured hydrocarbon gases each. TG thermogram of isothermal experiments conducted under various temperatures shows that above 773 K, the weight loss reaches 30 % and no more was observed. XRD patterns characterized that after each experiments, a-Fe, Nd oxychloride, Nd chloride, and Fe chlorides were formed, and the leaching residues remain only a-Fe. The yields of Nd, Dy, and Fe for the isothermal experiment were increased with temperature and peaked at 873 K. As PVC ratio increased, the yields of Nd, Dy and Fe were also increased. In this process, wastes were converted to the valuable resources by pyrolysis of PVC.