Kinetic Control of Rare Earth Element Separation via Interfacial Solvent Extraction and Low-Gradient Magnetic Fields.

The production of energy-efficient technologies and advanced electronics requires high-purity critical minerals, such as individually separated rare earth elements (REEs). Chemical REE separation processes rely on small differences in physicochemical properties (i.e., ionic charge and radii) to transport selective metal ions across liquid-liquid interfaces, making selective separation time-consuming and expensive. Incorporating another intrinsic property, ionic magnetic moment, alongside ionic radius may improve interfacial transport. We report here a novel batch solvent extraction system, termed magnetically assisted solvent extraction (MA-SX), controlled by the orientation of low-gradient magnetic fields generated by permanent magnets. We observe that the concentration of paramagnetic REE ions and the extractant ligand, di-(2-ethylhexyl)-phosphoric acid (D2EHPA), significantly influence ion transfer kinetics across an aqueous-organic interface under varying magnetic field gradient orientations. Comparisons among REEs with different magnetic moments show that MA-SX behavior correlates with ionic magnetic moments. Extraction of binary mixtures containing Dy-(III) and Y-(III) suggests paramagnetic and diamagnetic ions co-aggregate at low concentrations, reducing separation in the presence of low-gradient magnetic fields. At total metal concentrations above 50 mM, Dy-(III) and Y-(III) partition, with Y-(III) preferentially extracting into the organic phase due to D2EHPA's slight affinity toward Y-(III).