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| A new high-throughput Mach–Zehnder interferometry imaging capability at Pacific Northwest National Laboratory, developed for critical minerals and materials extraction research, enables direct spatiotemporal imaging of ion concentrations in magnetic fields and reveals sustained concentration waves and rare earth ion enrichment regions driven by magnetic field gradients. Photo Credit: Andrea Starr | Pacific Northwest National Laboratory |
Rare earth elements (REEs) are crucial for energy-related applications and are expected to play an increasingly important role in emerging technologies. However, these elements have very similar chemical properties and naturally coexist as complex mixtures in both traditional and unconventional feedstocks, making their separation challenging. Researchers in the Non-Equilibrium Transport Driven Separations (NETS) initiative used standard low-cost permanent magnets to induce a magnetic field gradient in solutions containing REEs. They found that these permanent magnets create local magnetic fields strong enough to lead to regions enriched in REE ions, with concentration increases of up to three to four times the concentration of the starting solution. Directly observing magnetic field–driven ion enrichment in real time, without intrusive probes that disturb the system, has long been a challenge. The development of a new high-throughput Mach–Zehnder interferometry imaging capability has now enabled visualization of these dynamics as they unfold.
Finding ways to separate REEs without using massive amounts of energy or specialty chemicals will be key to meeting the growing demand for critical minerals. This work provides the foundational observations and understanding necessary for advanced lanthanide separation using accessible, low-cost permanent magnets. This process is applicable to even dilute and unconventional domestic REE feedstocks, such as the millions of tons of mine tailings and produced water present across the United States, opening reliable new supply chains for critical materials. Strategies leveraging magnetic fields provide a scalable separation platform with reduced energy and chemical costs and improved economic viability, according to preliminary technoeconomic assessments.
Selective separation and crystallization are vital for recovering REEs from unconventional and secondary feedstocks such as produced water, mine tailings, and coal ash. However, the near-identical chemistry of lanthanides renders conventional methods inefficient and impractical for extracting REEs from dilute unconventional feedstocks and meeting the increasing demand for REEs. Magnetic separation offers an alternative approach by exploiting the differences in REE magnetic moments, but fields from low-cost permanent magnets were previously dismissed as too weak to drive selective ion transport and separation. NETS researchers demonstrated that the high magnetic field gradients generated by these low-cost magnets induce long-range, directed transport and spatial redistribution of paramagnetic lanthanides, such as dysprosium ions in solution. A newly developed high-throughput Mach–Zehnder interferometry imaging capability reveals the emergence of concentration waves and spatiotemporally resolved sustained ion enrichment, uncovering a dynamic balance between magnetic drift and other forces in solution. Calculations from a modified Poisson–Nernst–Planck model support these experimental observations and emphasize the importance of charge imbalance in the enriched regions under magnetic fields. This magnetically driven mechanism increases concentrations by three to four times that of the bulk solution. This enrichment results in the formation of magnetized domains that shift the local electrochemical potential of paramagnetic species, triggering dysprosium oxalate crystallization. These newly observed phenomena will be harnessed in a powerful, adaptive, field-responsive strategy to actively control interfacial energetics, expanding beyond traditional chemical functionalization and opening new avenues for controlling ionic behavior and separations. A conservative technoeconomic analysis suggests that compared with conventional methods, this approach achieves significantly reduced energy and chemical costs for separating paramagnetic REEs, offering a scalable new platform for critical metal recovery from complex domestic feedstocks.
Funding: This work was supported by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory, under the Non-Equilibrium Transport Driven Separations Initiative (NETS). ZF acknowledges the Department of Energy Science Undergraduate Laboratory Internship program.
Published in journal: Separation and Purification Technology
Authors: Giovanna Ricchiuti, Zachary Fox, Bruce Palmer, Mohammadhasan Dinpajooh, Ivani Jayalath, Yang Huang, Shuai Zhang, Evan Mondarte, Grant E. Johnson, Alan G. Joly, Jaehun Chun, Kevin Crampton, and Venkateshkumar Prabhakaran
Source/Credit: Pacific Northwest National Laboratory
Reference Number: ms011026_01
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