PNNL

The Science

Magnetic beneficiation has historically been used as a solid-phase pretreatment step to upgrade low-grade ores to higher-grade concentrates by removing waste material. Magnetic fields are currently being explored for atom- and energy-efficient scalable critical materials separations in solution. However, designing separation methods requires an understanding of how the magnetic properties of the relevant materials evolve throughout the extraction process. Researchers from the Non-Equilibrium Transport Driven Separations (NETS) Initiative studied a series of molecules combining four rare earth elements (REEs) with three industrially relevant precipitating agents to probe their individual magnetic behavior. They found that all the products are paramagnetic with properties that vary based on the magnetic moments and packing density of the specific metal ions, which provides key insights to guide reagent selection for selective extraction.

The Impact

REE-containing materials often have multiple different elements present, making separations key to maintaining a robust and reliable supply chain of these critical minerals. REEs are notoriously challenging to separate because they have similar chemical properties. Magnetic field-based separations are a potentially transformative approach for extracting REEs, but significant knowledge gaps exist about the magnetic properties of REE materials. The fundamental understanding developed in this work will enable the rational design of magnetic separation processes for efficient and selective recovery of critical REEs from complex and unconventional feedstocks, enabling a secure domestic supply chain of critical minerals to support economic and national security.

Summary

Magnetic separations present a promising approach for the recovery of REEs from complex mixtures, particularly when coupled with precipitation techniques that enhance process efficiency and selectivity. However, the magnetic properties of the REE materials typically encountered in the separations industry are not well characterized. Researchers synthesized a series of REE materials, combining four different REEs (praseodymium, neodymium, terbium, and dysprosium) with three common precipitating agents (hydroxide, oxalate, and dibutyl phosphate). All the materials showed typical paramagnetic behavior, with varying levels of response strengths. Particle morphology and crystallography analyses showed that the dibutyl phosphates were well-ordered metal-organic frameworks, the oxalates were crystals with mixed hydration states, and the hydroxides were mostly amorphous. Regardless of the degree of crystallinity, the effective magnetic moments aligned well with theoretical estimates based on the material and general structure. Within each REE series, the response of the different materials was determined by the size of the particles rather than the specific properties of the precipitating agent. This improved understanding of the magnetic properties of REE precipitates will guide the development of selective and efficient separation methods for critical minerals.

Contact

Elias Nakouzi, Pacific Northwest National Laboratory, elias.nakouzi@pnnl.gov 

Grant Johnson, Pacific Northwest National Laboratory, grant.johnson@pnnl.gov

Funding

This study was supported by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory, under the NETS Initiative. The ATR-IR, SEM, and XRD analyses were conducted at the Molecular Analysis Facility, a National Nanotechnology Coordinated Infrastructure site at the University of Washington (UW) with partial support from the National Science Foundation via awards NNCI-2025489 and NNCI-1542101. The authors acknowledge the use of a SQUID Magnetometer supported by the U.S. National Science Foundation through the UW Molecular Engineering Materials Center, a Materials Research Science and Engineering Center (DMR-2308979).