Selective Extraction of Rare Earth Elements from NdFeB Scrap by Molten Chlorides

Abstract

With rapid growth in the use of NdFeB magnets and growing concerns for environmental protection as well as conservation of rare earths (REs), the recycling of NdFeB magnet scrap is becoming a hot issue for current society. In this study, it is demonstrated that the rare earths in a NdFeB magnet can be selectively extracted using molten MgCl 2 −KCl salts at temperatures of 600−1200°C. After crushing to granules, the scrap was subjected to molten chlorides in a dry argon atmosphere. The reaction process between NdFeB scrap and molten MgCl 2 −KCl was directly observed using a high-temperature contact angle measuring instrument to clarify the phenomena that occur when rare earth chlorides are formed in situ. Furthermore, the effects of reaction temperature, holding time, and mass ratio of MgCl 2 / NdFeB were investigated to transform REs in the scrap to RECl 3 as completely as possible. The reaction products were examined with the necessary analytical techniques including SEM, EDS, XRD, and ICP. The overall extraction efficiency for REs was found to be more than 90% under the optimum operating conditions. The obtained RECl 3 in the molten MgCl 2 −KCl can be processed with molten salt electrolysis for the direct production of Mg−Nd alloy.

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

“…Itoh et al [34] used the same method but using a different salt. Hua et al [70] adapted the process by combining several salts to increase selectivity.…”

“…Hua et al [70] investigated the kinetics and mechanism of REEs extraction using molten salt. The mechanism of extraction suggested from their study is depicted in Fig.…”

“…The main reasons that gas phase extraction of RE metals is difficult to apply are: firstly, RE chlorides (RECl) are less volatile and, [70] therefore, difficult to separate from other less volatile metal chlorides, especially from alkaline-earth chlorides; secondly, extraction of the REs by gas phase chlorination requires relatively high temperatures and long reaction times; thirdly, RE chlorides have a very similar volatilities, so that mutual separation is not expected in the sublimation processes. In Murase et al [29,30] Tables 2 and 3), the RE chlorides form halogen-bridged complex formers with alkali metal chlorides which leads to vast increase in vapor pressure and transport of the lessvolatile RECl through the reactor, which has a temperature gradient (sublimation chamber).…”

“…Approximately 80 % of Nd and Dy could be efficiently extracted as chloride following 12 h of reaction. The technique was modified by Hua et al [70] by using the binary system MgCl 2 -KCl, which exhibits a lower melting point and viscosity, as well as lower volatility compared with pure MgCl 2 .…”

Large batch recycling of waste Nd–Fe–B magnets to manufacture sintered magnets with improved magnetic properties

“…In recent years, about 100,000 tons sintered magnets are produced each year [5]. However, the scraps generated during machining of sintered magnets amounts to about 25 wt.% of the final products [6].…”