Hydrophobic Eutectic Solvents for Tailored Metal Separation and Recycling

DESignSX proposes the application of bio-inspired non-ionic hydrophobic eutectic solvents (DES) to the solvent extraction (SX) separation of lanthanides (Ln) based on the understanding of these complex mixtures that are defined by hydrogen-bonded supramolecular self-assembly. Sustainable metallurgy stands uniquely poised to reduce the environmental impact of existing processes whilst recovering the metal value in end-of-life devices, thereby closing the resource loop. Despite their growing demand and geopolitical criticality, Ln separation remains technologically challenging due to the small monotonic variation in their properties, negatively affecting the economics of their recycling. DESignX seeks to exacerbate the steric factors defining the interactions between Ln and ligands, dictating the ensuing complex geometries and mutual separation selectivity, through the inclusion of complexing agents as components of molecularly crowded DES. By carefully selecting the DES phase binary components, the energy penalty associated with the structuration of the apolar phase may be rationally adjusted to increase the selectivity between adjacent Ln versus the same extractant in conventional SX. Given that the separation of adjacent Ln occurs over dozens of counter-current extraction stages, even seemingly small increases in the separation factors yield measurable environmental and economic gains. DESignSX rely on a tandem experimental-computational approach spanning multiple time and size scales, from a molecular description of pair-wise interactions to laboratory-scale process optimisation. DESignSX will overcome the traditional SX issues of complex flowsheets, third-phase formation, toxicity of the organic diluent through the inclusion of bio-derived components, and entrainment losses, whilst improving the selectivity of the separation. DESignSX outcomes are expected to be transferable to other critical SX separations.