Oak Ridge National Laboratory,
Keywords: solvent extraction, dissolution, theory, rare earth elements
Summary:Selective separation of rare earth elements (REE – lanthanides, scandium, and yttrium) poses such a formidable challenge that it has been recognized as one of “seven chemical separations to change the world”. These elements have found widespread applications in advanced technologies and are found in many consumer products such as smartphones and electric vehicles. However, REEs are still separated using legacy solvent extraction processes that are inefficient, sometimes requiring hundreds of stages to recover individual elements in high purity. This is because these elements exist predominantly in 3+ oxidation state and their ionic radii decrease across the lanthanide series on average by only 0.01 Angstrom per unit increase in atomic number. The Critical Materials Institute (CMI), one of U.S. DOE Energy Innovation Hubs, focuses on accelerating the discovery of critical energy technologies. Developing efficient and economically sound processes to advance rare earth element separations is one of the outstanding research priorities for the CMI. An overview of emerging technologies for rare earth element separations developed under the umbrella of CMI include a) the design of extractants with improved properties for high-throughput solvent extraction using centrifugal contactors and b) the development and scalability of supported membrane solvent extraction process, as well as c) the forthcoming selective leaching of rare earth elements from ores using size-selective molecular recognition tailored (SMART) lixiviants. Furthermore, the use of molecular design methods that guide the development of organic ligands possessing essential properties to realize selective rare earth element separation will be discussed.