Chemical isolation of rare earth elements (as pure rare earth oxides) from Nd-Fe-B magnets and Ni-MH batteries

Abstract

Rare earth elements (REEs) are increasingly in demand for their usage in electric vehicles, permanent magnets, and rechargeable batteries. However, the limited supply of REEs and the significant environmental impact associated with their extraction and concentration have prompted countries to explore recycling options for REE-bearing waste. Despite this, the lack of an efficient recycling method remains a challenge. This study proposes a chemical-based approach towards the recovery of rare earth oxides (REOs), which facilitates a clean separation of REOs with purities exceeding 99.1 wt% and 97.1, along with recovery rates more than 99.3 wt% and 97.1, respectively, from permanent Nd-Fe-B magnets and Ni-MH batteries. Initially, REEs (La, Ce, Nd, Pr, Dy, and Sm) were thermally isolated from Ni- and Fe-based metallic alloys, while still containing impurities. The impurities were subsequently removed via an oxalate chemical separation. Thermodynamics of REE oxalate formation indicated that the precipitation of pure REE oxalates occurs only at pH≈0.0. As the pH increases, impurities such as Ni are introduced into the REO products. The abundance of C2O42- decreases the selective separation, whereas HC2O4- recovers REEs from the leachate at pH≈0.0. The proposed pH range, as indicated by the speciation plots, not only restricts the trace of contamination but also maximizes the efficiency of the process. XPS analysis of the chemically isolated REOs indicated no sign of major impurities. The pure REOs recovered in this study can be used as a high-purity precursor for other applications. Overall, this chemical-based approach offers a promising method for recycling REEs, contributing towards meeting the increasing demand for these critical elements.