Development of a Process to Recycle NdFeB Permanent Magnets Based on the CaO-Al2O3-Nd2O3 Slag System

Abstract

Nd, Pr and Dy are critical raw materials as major components for rare earth permanent magnets (REPM). These are integral for several components placed for example within electric vehicles and wind turbine generators. REE primary production is mainly realized in China (~80%) and no REPM recycling industry has been established. Hydrometallurgical recycling routes lead to iron dissolution (66 wt. % Fe in REPM), while pyrometallurgical approaches that utilize SiO2 risk contaminating the produced iron phase. A two-step process is presented that (i) creates an FeOx-CaO-Al2O3-REE2O3 molten slag at 1500 °C through oxidative smelting and (ii) separates an iron-depleted slag phase (CaO-Al2O3-REE2O3) and a molten iron phase via carbothermic or metallothermic reduction at 1700–2000 °C. The slag has been designed as a selective collector phase and the REE2O3 loading within the bulk slag can reach up 25 wt. % REE2O3 at 1700 °C. The contained minerals within the slag exhibit >40 wt. % REE (a higher REE concentration than in the initial REPM). The resulting phases are characterized via ICP-OES, CS and SEM-EDX. In addition, the first results with regard to the downstream hydrometallurgical processing of the CaO-Al2O3-REE2O3 slag are presented aiming at the recovery of REE2O3, as well as of CaO and Al2O3. The latter compounds are to be reused during the first process step, i.e., the oxidative smelting of REPM. Slag leaching with methane sulfonic acid (MSA) and separation with alternative methods, such as solvent extraction, seems promising. Future work will include slag filtration with the aim to separate REE-rich solid phases (minerals) from the slag and also molten salt electrolysis of the produced REE2O3 oxides.