Development of an innovative process involving the use of ionic liquids for the recovery and purification of rare earths from permanent magnets and NIMH batteries

Abstract

Background: Nowadays, the industry trends are reflecting an increase in the consumption of products containing rare earth elements (REEs), which leads to the generation of several REE-containing residues such as spent permanent magnets (SPM), permanent magnet swarf (PMS), and nickel metal hydride (NiMH) batteries. Methods: Due to the risk of supply and to decrease the dependency of Europe in obtaining REEs, an innovative process for obtaining REEs in the form of rare earth oxalates (REOx) that can be easily transformed to an xide mixture by calcination is proposed. The  proposed method includes leaching of REEs from SPM, PMS, and NiMH batteries using different solvents such as ionic liquids and/or mineral acids; precipitation of REE in the form of REOx and purification of the final products by an ionic liquid extraction (ILE) process for removing the impurities using Cyphos 101 as ionic liquid. Intensive research, based on laboratory tests, is described for each of the parts of the process with the aim of providing optimized results. Results: In this study, >99% recovery of the REE initially present in the leachates after the leaching phase is achieved, with a purity of the REOxafter the precipitation and purification steps higher than 95%. Conclusion: A novel and innovative process for the extraction of REEs from secondary sources has been investigated in this paper, demonstrating strong potential for its implementation. The REEEs recovery rate and the purity obtained  together  with the low environmental impact of this process compared to conventional ones can contribute to a greener future where the usage of REEs will presumably be even more relevant.