Author(s)

T. Itakura, R. Sasai & H. Itoh

Abstract

The hydrothermal treatment of used Nd-Fe-B sintered magnet was investigated in order to recover the rare-earth resources and boron (B) efficiently. Commercially available Ni-coated Nd2Fe14B sintered permanent magnet was hydrothermally treated for 6 hours at 110°C in a mixed aqueous solution of hydrochloric acid and oxalic acid. As a result, more than 99% of neodymium (Nd) metal contained in the magnet was collected as a solid powder of Nd2(C2O4)3·xH2O with purity of 99.8%. The recovery technique of B as a reusable precipitate of Ca2B2O5·H2O contained in the treated water was also developed. As a result, it was found that hydrothermal treatment using calcium hydroxide is very effective in collecting B contained in the aqueous media. Experimental results on optimization for hydrothermal treatment conditions revealed that more than 99% of B was collected from the treated water. Thus, the present hydrothermal treatments are effective at collecting resources from Nd-Fe-B sintered magnet. 1 Introduction Nd-Fe-B permanent magnets with excellent hard magnetic properties are widely applied to various advanced electromagnetic, electromechanical and electronic devices such as voice coil motors, magnetic resonance imaging, etc. Thus, the amount of industrial production of Nd-Fe-B permanent magnets has been increasing year by year. The increment of the discharged amount of used magnets will be anticipated to cause the depletion of their disposal sites, which is one of the serious problems in waste management in Japan. Moreover, most of the rare-earth resources utilized in Japan are imported from various foreign

Keywords