Solvent Extraction

The chemical and physical properties of the final application using rare earth elements (REEs) are specific to the different REEs and in most cases, these properties depend on the purity of the REE used. Since RE ores contain a mixture of all the lanthanides plus yttrium, and because the lanthanides and yttrium have similar chemical properties, producing such high purities is a challenge. Currently, this process step commonly called RE separation or RE refinery is done by solvent extraction (SX). Although several companies and research teams are looking for alternative processes, SX remains the only technology used in industry. Solvent extraction is a combination of chemistry and technology. This chapter presents the chemistry and the technology behind the RE separation process and their consequences on the economics and the environmental footprint of the REE industry. Different combinations of aqueous solutions and organic molecules can be used at industrial scale, but only an overall comparison from ore leaching to the separated individual and blended RE oxide including environmental assessment can decide the best choice for each specific application. Companies mastering the modeling of the REE separations can design and drive an REE separation unit. Up to now all the industrial units of RE separation use SX operated in mixer-settlers (MS). This technology is mature and very robust but leads to high CAPEX and high REEs inventory. Several teams are trying to overcome this drawback by working on new processes as replacing MS by columns, or by replacing the solvent with a solid phase leading to processes called Solid Phase Extraction (SPE). These efforts are also reviewed.