G. Ricchiuti, I. Jayalath, Y. Huang, M. Dinpajooh, Z. Fox, A.G. Joly, K. Crampton, A. Ritchhart, E. Nakouzi, G.E. Johnson, V. Prabhakaran
Pacific Northwest National Laboratory (PNNL),
United States
Keywords: separation, rare-earth elements, critical materials, field-driven separation
Summary:
Securing reliable domestic supplies of critical minerals and materials (CMMs) such as rare earth elements (REEs), nickel (Ni), and cobalt (Co) is essential for sustaining advanced manufacturing, technological innovation, and national security. Yet their nearly identical chemical properties make selective separation one of the most persistent challenges in the metallurgical supply chain. Current industrial extraction and purification routes—based on solvent extraction or ion exchange—are effective primarily for concentrated feedstocks and are associated with high chemical, energy, and environmental costs. With increasing global demand and geographically constrained reserves, developing new, efficient, and sustainable separation routes has become imperative. In this work, we demonstrate magnetic-field-driven strategies for the selective separation of CMMs that exploit intrinsic differences in the magnetic properties of REEs and transition metals, enabling quantifiable fractionation of these ions directly from mixed feedstocks. Contrary to the long-standing assumption that magnetic forces are too weak to influence solvated ions, our results using a new spatiotemporally resolved digital off-axis holography (DOAH) capability reveal that inhomogeneous magnetic-field gradients can generate measurable ion enrichment and depletion zones governed by magnetic-susceptibility differences. This experimentally observed redistribution forms the physical basis for developing two distinct separation platforms: magneto-chemical and magneto-electrochemical. The magneto-chemical platform enables selective precipitation of lanthanides. In Dy/Nd mixtures, applying a magnetic field during sodium oxalate addition produced a 10–15 % higher Dy recovery in a single extraction cycle, demonstrating field-directed crystallization driven by paramagnetic contrast. The magneto-electrochemical platform, in turn, integrates magnetic and electric fields to separate transition metals. In the Co/Ni system, despite nearly identical redox potentials, contrasting magnetic susceptibilities induce magnetohydrodynamic ion transport, yielding tunable electrodeposition of Ni over Co with a selectivity factor of ~4 in a single separation cycle. Together, these two strategies, magneto-chemical selective precipitation and magneto-electrochemical extraction redefine how external fields can be harnessed for CMM separation. This work bridges fundamental insights into magnetic-field-modulated ion transport and interfacial reactivity with practical separation technologies, offering low-waste, energy-efficient, and economically viable pathways for the targeted recovery of REEs and transition metals from complex or dilute unconventional feedstocks.