Supercritical Fluid Extraction for Urban Mining of Rare Earth Elements

Abstract

For moving toward a sustainable future and building the circular economy, there is a push toward waste valorization and urban mining. NiMH batteries and NdFeB magnets contain significant amounts of rare earth elements (REEs). These elements offer unique physicochemical properties; thus, they have become a key component of many critical green technologies and some are identified as critical material and initiatives have begun to recycle them from postconsumer products. Conventional recycling processes rely on pyrometallurgy or hydrometallurgy. The former is energy intensive, generating greenhouse emissions, while the latter consumes large volumes of acids and organic solvents and generates vast amounts of hazardous waste. Here, we develop an environmentally sustainable recycling process, in which we utilize supercritical fluids to extract REEs from end-of-life products. We believe that supercritical fluid extraction (SCFE) process is a viable alternative to pyrometallurgy and hydrometallurgy for urban mining of REEs in an economical and environmentally benign manner.