Can coal mines provide rare earth elements?

Michael Vanden Berg, geologist with the Utah Geological Survey, examines a coal outcrop near Utah's old Star Point mine. Credit: Lauren Birgenheier/University of Utah.

As the world seeks to transition away from fossil fuels, it may seem ironic that coal mines could play a role in this shift by providing essential minerals for renewable energy.

Researchers from the University of Utah have discovered elevated concentrations of rare earth elements (REEs) in active coal mines along the Uinta coal belt in Colorado and Utah.

These findings, published in the journal Frontiers in Earth Science, suggest that coal mines could serve as a secondary source of these critical minerals.

Rare earth elements are vital for high-tech applications and renewable energy technologies. However, most of these elements are currently sourced from overseas, creating supply chain vulnerabilities.

This study, led by Associate Professor Lauren Birgenheier, indicates that mining for REEs alongside coal could help mitigate these issues.

“The idea is that if you’re already moving rock for coal, could you also extract some of these valuable minerals?” Birgenheier explained.

The research found that REEs are concentrated in fine-grain shale units located above and below the coal seams. This discovery was part of the Carbon Ore, Rare Earth and Critical Minerals (CORE-CM) project, in collaboration with the Utah Geological Survey and Colorado Geological Survey.

Michael Free, a professor of metallurgical engineering and co-author of the study, emphasized the importance of finding domestic sources for these materials.

“When we talk about ‘critical minerals,’ much of the concern is about the supply chain and processing,” Free said. “This project explores alternative, unconventional domestic sources for these materials.”

Previous studies have documented the association between coal and REE deposits in other regions, but little data had been collected in Utah and Colorado until now. The goal of this phase-one project was to determine whether REE enrichment in these coal fields could provide a valuable byproduct for the coal mining industry.

The researchers analyzed 3,500 samples from 10 mines, four mine waste piles, seven stratigraphically complete cores, and some coal ash piles near power plants. They found that while the coal itself is not enriched in REEs, the surrounding rock formations, such as siltstone and shale, showed promising concentrations.

Two methods were used to measure REE levels in the samples. A hand-held X-ray fluorescence device provided quick field readings, while more detailed analysis was performed in the lab using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Samples with concentrations higher than 200 parts per million (ppm) were deemed “REE enriched.”

The Department of Energy has set 300 ppm as the threshold for economically viable rare earth mining. While most samples in the study did not reach this level, some showed significant enrichment. The next steps involve determining the total amount of rare earth ore present, in collaboration with the University of Wyoming and the New Mexico Institute of Mining and Technology.

These findings open up the possibility that coal mines could become a valuable source of rare earth elements, supporting the transition to renewable energy and high-tech industries. Further research will be crucial to understanding the full potential of this resource.