Crucial 'rare earth elements' discovered in coal mines in the US

In a surprising twist, rare earth elements, traditionally sourced from overseas, have been discovered within coal mines in the United States.

Recent research has uncovered significant concentrations of rare earth elements (REEs) in active coal mines in the Uinta coal belt of Colorado and Utah. These elements are crucial for the transition to renewable energy and the advancement of high-tech applications.

Finding rare earth elements in coal mines

A study led by the University of Utah has documented elevated levels of REEs in these coal mines and opened the possibility of extracting these critical minerals.

This dual resource stream could provide valuable metals used in renewable energy technologies, according to Lauren Birgenheier, an associate professor of geology and geophysics at the university.

“The model is if you’re already moving rock, could you move a little more rock for resources towards energy transition?” Birgenheier explains. “In those areas, we’re finding that the rare earth elements are concentrated in fine-grain shale units, the muddy shales that are above and below the coal seams.”

Rare earth element potential in Utah and Colorado

The link between coal and REE deposits has been established elsewhere, but little data had previously been gathered or analyzed in Utah and Colorado’s coal fields. The initial phase of this project aimed to collect additional data to determine if these deposits were worth pursuing in the West.

“The goal of this phase-one project was to collect additional data to try and understand whether this was something worth pursuing in the West,” Michael Vanden Berg, Energy and Minerals Program Manager at the Utah Geological Survey, elaborates. “Is there rare earth element enrichment in these rocks that could provide some kind of byproduct or value added to the coal mining industry?”

Researchers analyzed 3,500 samples from 10 mines, four mine waste piles, seven stratigraphically complete cores, and some coal ash piles near power plants. The results were promising.

“The coal itself is not enriched in rare earth elements. There’s not going to be a byproduct from mining the coal, but for a company mining the coal seam, could they take a couple feet of the floor at the same time? Could they take a couple feet of the ceiling? Could there be potential there? That’s the direction that the data led us,” Vanden Berg concluded.

Economic viability of rare earth elements

To measure the levels of rare earths in the samples, the team used two methods: a hand-held device for quick field readings and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in an on-campus lab.

“We’re mostly using this portable x-ray fluorescence device, which is an analysis gun that we hold to the rock for two minutes, and it only gives us five or six of the 17 rare earth elements,” Birgenheier says.

If samples showed concentrations higher than 200 ppm, a more comprehensive analysis was conducted using mass spectrometry.

The Department of Energy has set 300 ppm as the minimum concentration for rare earth mining to be economically viable.

For this study, concentrations greater than 200 ppm were considered “REE enriched.” The study found the highest prevalence of such concentrations in coal-adjacent formations of siltstone and shale, while sandstone and the coal itself were mostly devoid of rare earths.

CORE-CM project

This research was conducted in collaboration with the Utah Geological Survey and Colorado Geological Survey as part of the Department of Energy-funded Carbon Ore, Rare Earth and Critical Minerals (CORE-CM) project.

The findings will support a grant request for an additional $9.4 million in federal funding to continue this promising research.

While these metals are essential for U.S. manufacturing, especially in high-end technologies, they are predominantly sourced from overseas.

Michael Free, a professor of metallurgical engineering and the principal investigator on the DOE grant, highlights the importance of this project.

“When we talk about them as ‘critical minerals,’ a lot of the criticality is related to the supply chain and the processing. This project is designed around looking at some alternative unconventional domestic sources for these materials,” Free explained.

New era of critical mineral research

To date, the team has analyzed 11,000 samples, far exceeding the number used in the published study.

The next steps involve determining how much rare earth ore is present, likely in collaboration with colleagues at the University of Wyoming and New Mexico Institute of Mining and Technology (NMT).

This innovative research could revolutionize the way we view coal mines, transforming them from relics of the fossil fuel era into valuable sources of critical minerals for the future of renewable energy.

The full study was published in the journal Frontiers of Earth Science.

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