Rare-Earth Partitioning with Liquid Iron During Sulfidized Magnets Vacuum Treatment

An effect previously observed in magnet recycling experiments is further investigated in this work. At high temperatures (1800 °C) and moderate vacuum (0.01 bar) certain heavy rare earth elements are found to selectively partition into a metallic iron phase produced by thermal decomposition from a molten sulfide phase. Works in the literature have established that rare earth elements suppress the concentration of sulfur strongly in liquid iron at 1600 °C, but the behavior of heavy rare earth elements in this context remains uncertain. Herein, experimental results using magnet simulants with heavy rare earth elements – terbium, dysprosium, and erbium – are reported, using concentrations 10 × higher than in magnets, in order to investigate the possible saturation of the iron phase. SEM/EDS analysis showed that terbium and dysprosium partitioned to the metal at low concentrations, approximately 0.50% by weight.