EARTH

[3801-11-03] Recovery of rare earth elements from rare earth magnets scraps by Fe-Si alloys and sodium silicate fluxes

○Chompunoot Wiraseranee¹, Rinat Mirvaliev¹, Satoshi Okada¹ (1. Mitsubishi Materials Corporation)

Chairman: Chompunoot Wiraseranee （Mitsubishi Materials Corporation）, Liu Hui (Central South University)

Keywords:rare earth, magnet, sodium silicate, slag, recycling

Rare earth elements (RE), such as neodymium (Nd) and dysprosium (Dy), are the key elements of rare earth magnets which are widely used in home appliances and hybrid-electric vehicles. However, the limited resources of the elements have resulted in the lack of rare earth elements supply. To cope with the problem, various recycling technologies have been developed in recent years. In this research, the new pyrometallurgical separation process of rare earth elements and iron from magnet scraps was developed. The separation was carried out by using Fe-Si liquid alloys and sodium silicate fluxes (Na₂O-nSiO₂, n ≤ 2) at 1300°C. According to the thermodynamic calculations, the coexistence of Si in Fe-Si alloy and SiO₂ in sodium silicate flux brought an oxygen potential to the values at which rare earth elements were oxidized and iron was remained in a metallic phase. From experiments, it was revealed that the oxidized rare earth elements dissolved into the molten fluxes to form Na₂O-SiO₂-RE₂O₃ slags which contained less than 1wt.% of iron. Meanwhile, iron was absorbed into the Fe-Si liquid alloys with no rare earth elements remained in the alloys after separation. The recovery efficiencies of both rare earth elements and iron of 99% were achieved. In the presentation, the principle of separation will be introduced. Experimental results and the effectiveness of the separation at various conditions, such as separation time, Fe-Si alloys and slag compositions, will be discussed.