Separation of neodymium from FeNd alloy and the preparation of porous iron alloy by chemical dealloying in molten chlorides: Application to the recovery of NdFeB wastes

Neodymium-iron-boron (NdFeB) magnets are the rare earth products with the largest output, and their recycling is of significance for the sustainable development of rare earth resources. Currently, the recycling technology of NdFeB wastes is more concerned with the recovery of rare-earth elements, while iron is regarded as a low-value by-product. In this work, chemical dealloying method in molten chlorides was proposed to separate neodymium from FeNd alloy and simultaneously to prepare porous iron alloy. The effects of the molar ratio of reactants, dealloying temperature and time on the separation efficiency of neodymium were investigated. The maximum separation efficiency of neodymium from FeNd alloy can reach 96 %. The separation process of neodymium and the formation process of porous iron alloy were estimated based on the ICP, XRD, XPS, SEM-EDS analyses of recycled products. Neodymium was separated from FeNd alloy by the reaction with Nd(III) ions to form Nd(II) ions in molten chlorides, while the porous iron alloy was formed. The formed Nd(II) ions can be transformed into Nd(III) ions and metallic neodymium particles by the disproportionation reaction. In the process, Nd(III) ions can act as a complement to react with FeNd alloy. And neodymium was recovered in the form of metallic neodymium and NdOCl from the chloride melt and the rinsing solution of porous iron alloy, respectively. The formed porous iron alloy had the surface area of unit volume in the range of (2 ∼ 20) × 104 cm2 cm−3, the pore width around 10 nm and good hardness. The porous iron alloy is a high value-added product.