Recovery of rare earth metals from voice coil motors using bis(trifluoromethylsulfonyl)amide melts by wet separation and electrodeposition

Abstract

In this study, a new recycling process for rare earth metals was developed for voice coil motors (VCMs) from hard disk drives. For the wet separation process, the leaching behavior of finely ground oxidized VCM powder in 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methane sulfonamide; HN(SO2CF3)2, (HTFSA) aqueous solution was studied. The kinetics of the leaching process for the rare earth metals was explained using the shrinking core model. Then, the selective titration of Fe(OH)3 precipitates was determined from the pH-log[Mn+] diagram. The ionic conductivity of the obtained metallic-TFSA melts obeyed the Arrhenius law and the Vogel–Tamman–Fulcher (VTF) parameters were estimated from empirical data. For the electrodeposition process, the reduction behavior of Nd in the metallic-TFSA melts was investigated using cyclic voltammetry, and it was also studied under the potentiostatic condition of −3.2V at 493K. The deeper layer of the electrodeposits consisted mainly of Nd metal, which was confirmed by XPS. The oxygen content decreased to less than 0.1% at a depth of 1.0μm. Thus, the series of recycling processes developed here enabled Fe in VCMs to be selectively removed by wet separation and metallic Nd to be efficiently recovered by electrodeposition.