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 degrees 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 degrees 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 x 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.