Extraction of Rare Earth Elements as Oxides from a Neodymium Magnetic Sludge
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TRODUCTION
THE production of Nd-Fe-B magnets has increased recently because improvements in the performance of various products such as the motors in home electrical appliances and the voice coil motors in computer hard disk drives have been realized because of the strong magnetic power of Nd-Fe-B magnets. In addition, an increase in Nd-Fe-B magnet production is expected because of an increase in the demand for hybrid vehicles and electrical vehicles as a result of growing global environmental concerns.[1–3] A large amount of magnetic sludge is generated in magnet production processes like cutting and grinding. The magnetic sludge may be as much as 30 pct or more of the production volume.[3–5] Because the sludge is regarded as a significant source of rare earth elements (Nd, Dy, and Pr), several kinds of recovery processes for rare earth elements as a source material have been investigated.[3–11] The separation of rare earth elements and iron has focused mainly on studies into the recovery of rare earth elements from magnetic sludge because iron accounts for roughly half of the magnets. Hirota et al.[7] reported the potentiality for separating the rare earth oxide and transition metals from the magnet sludge by arc melting based on the difference in oxygen affinity between the rare earth elements and transition metals. Murase MASASHI NAKAMOTO, Specially Appointed Assistant Professor, YOHEI KATAYAMA, Graduate Student, and TOSHIHIRO TANAKA and TAKAIKU YAMAMOTO, Professors, are with the Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan. Contact e-mail: [email protected] KENJI KUBO, formerly Graduate Student, Graduate School of Engineering, Osaka University, is now Engineer, with Steel Sheet, Plate & Structural Steel Company, Sumitomo Metal Industries, Ltd., Kashima, Ibaraki 314-0014, Japan. Manuscript submitted August 17, 2011. Article published online December 14, 2011. 468—VOLUME 43B, JUNE 2012
et al.[8] studied the recovery of rare earth elements from sludge by chemical vapor transport by using the differences in the temperature dependence of the formation– decomposition equilibria of the vapor complexes. In their work, chlorine and aluminum chloride were used as a chlorinating agent and a transporting agent, respectively. Uda[9] proposed a recovery process for rare earth elements by the selective chlorination of rare earth elements using FeCl2 as a chlorinating agent. With activated carbon as a deoxidation agent, in this study, the Fe metallic state is retained without chlorination. Shirayama and Oakabe[4] used molten salts like MgCl2 and ZnI2 as extraction media for the recovery of rare earth elements. Takeda et al.[10] investigated the extraction of rare earth elements based on the phase equilibria of the Ln2O3-LnFLi2O-LiF system (Ln = Nd and Dy). Nishihama et al.[11] studied the leaching properties of rare earth elements from magnetic sludge using several mineral acids. The method using the difference in oxygen affinity between the rare earth elements and Fe is considered to be
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