A molten salt process for producing neodymium and neodymium-iron alloys

The production of low-cost neodymium metal in a stirred tank reactor by the reduction of Nd₂O₃ with sodium in the presence of CaCl₂−KCl−NaCl melts by the overall reaction Nd₂O₃+3CaCl₂+6Na→2Nd+3CaO+6NaCl at ∼750 °C is described. The metal produced is recovered from the salt medium by dissolving it in a Nd−Zn or Nd−Fe alloy pool. In the case of Nd−Zn alloy pools, product yields (percentages of theoretical neodymium produced) in excess of 94 pct are obtained when using salt ratios,i.e., the amounts of salt per gram of neodymium produced, ≥3.5 and excess reductant ≥10 pct. The alloy produced is of high quality, and following vacuum distillation of the zinc, can be used in producing General Motors’ MAGNEQUENCH alloy for permanent magnets. In the case of Nd−Fe pools, the yield is also ∼95 pct with a salt ratio as low as 3.5. The yield is found to depend on the salt composition and salt ratio, and to decrease at salt ratios below 3.25. Stirrer position has little effect on yield, while increasing the temperature and placing fins in the reactor increase the yield. The Nd−Fe alloy produced is of as good quality as that produced using Ca reductant and is suitable for direct use in preparing the MAGNEQUENCH alloy.