Influencing Factors on the Melting Characteristics of NdFeB-Based Production Wastes for the Recovery of Rare Earth Compounds

Abstract

During the processing of neodymium-iron-boron (NdFeB) magnets, the blank is ground into its final form. During this step, there are slurries arising which contain major amounts of magnetic materials as well as lubricative and abrasive particles from the grinding disk. Since there is no tailor-made recycling process for this kind of wastes, a thermal treatment in combination with a melting step is proposed in this paper as a possible way for separating rare earth compounds from iron and other accompanying elements. During this process, a metallic Fe-based phase is separated from a rare-earth-containing oxide phase. Pretreatment has to be performed in order to separate the remainder of the cooling lubricant from the grinding process. Besides, the contents of accompanying elements such as oxygen have to be adjusted, since these elements can influence the melting process and phase separation. This paper deals with the factors which enable melting and phase separation by considering different input materials and the needed pretreatment. An oxygen content of more than 7 wt% needs to be maintained after the oxidation to enable phase separation during the melting. In addition, the presence of carbon is essential to avoid the formation of iron oxides. By this way, rare earth oxides from various NdFeB materials can be extracted with a high output and purity. This investigation shows that it is also possible to achieve an oxygen content of more than 7 wt% in different scraps produced by means of a thermal treatment. This provides an opportunity for making the recycling concept suitable for various kinds of scrap.