Selective extraction of rare earth elements and cobalt from iron residue containing rare earth using mechanical activation and reductive leaching method

Abstract

NdFeB waste is an important rare earth secondary resource, which is usually treated by hydrochloric acid preferential method in traditional industrial process. Herein, leaching residue containing about 0.5–1 % rare earth elements (REEs) and a small amount of cobalt is generated as a by-product in the process. The leaching residue is mainly composed of iron oxide and generally sold to steelmaking plants, resulting in the waste of REEs and cobalt resource. An efficient recycling process is proposed for selectively extracting REEs and cobalt from the iron residue containing rare earth by mechanical activation and reductive leaching method based on mineral liberation analysis (MLA) and thermodynamic analysis. By analyzing the composition of the raw materials, magnetite and limonite are in an encapsulated state with rare earth minerals. REEs and cobalt are mainly present in the rare earth aluminate phase. To achieve deep extraction of REEs and cobalt, the first step is to change the insoluble phase of iron residue by mechanical activation method. During this process, the crystal structures of Fe2O3 and Fe3O4 in the iron residue containing rare earth are disrupted and transformed into amorphous states. During the reductive leaching process, part of the iron is converted into divalent. The iron in the leaching solution can be removed by hematite method and achieved phase reconstruction. Thus, REEs and cobalt can be extracted selectively from leaching residue of NdFeB waste.