高温におけるNd₂O₃-Na₂B₄O₇擬2元系の相関係とネオジム磁石のリサイクルへの応用

抄録

A high temperature recycling process of neodymium magnets using B₂O₃ flux has been reported. However, the B₂O₃ flux shows a poor fluidity of the slag. For this purpose of solving the problem, present work considers the use of Na₂B₄O₇ with lower viscosity than the B₂O₃ flux.

The phase equilibria for the Nd₂O₃-Na₂B₄O₇ pseudo binary system was investigated in the temperature range from 1460 K to 1780 K. We found that this pseudo-binary system forms the homogeneous melt in the concentration range of from 16 mass％Na₂B₄O₇ to 20 mass％Na₂B₄O₇ and over 55 mass％ Na₂B₄O₇ at 1673 K. Based on the determined this diagram, the feasibility study of the recycling process of the neodymium magnets using Na₂B₄O₇ flux was carried out 20 kg and 100 kg high frequency induction furnace. When neodymium magnets and an EV rotor were melted with Na₂B₄O₇ in a carbon crucible, the rare earth elements of Nd, Pr, Dy and Tb in the magnets and rotor were enriched to the Na₂B₄O₇ slag phase and the iron in the magnets and the rotor were contributed to the Fe-C alloy phase. The oxalate precipitation method was used for the recovered Nd₂O₃-Na₂B₄O₇ slag, more 99 mass％ purity ratio of RE_xO_y was recovered.

Fig. 3　Liquidus lines and phase relations for the Nd₂O₃-Na₂B₄O₇ pseudo binary system.