By Brian Maffly,
University of Utah

New research documents elevated levels of these metals, needed for energy transition, above and below coal seams in Utah and Colorado.

Deposits of designated critical minerals needed to transition the world’s energy systems away from fossil fuels may, ironically enough, be co-located with coal deposits that have been mined to produce the fossil fuel most implicated in climate change.

Now, research led by the University of Utah has documented elevated concentrations of a key subset of critical minerals, known as rare earth elements, or REEs, in active mines rimming the Uinta coal belt of Colorado and Utah.

These findings open the possibility that these mines could see a secondary resource stream in the form of metals used in renewable energy and numerous other high-tech applications, according to study co-author Lauren Birgenheier, an associate professor of geology and geophysics.

“The model is if you’re already moving rock, could you move a little more rock for resources towards energy transition?” Birgenheier said. “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.”

A Search for Alternate Sources of Rare Earths

This research was conducted in partnership with the Utah Geological Survey and Colorado Geological Survey as part of the Department of Energy-funded Carbon Ore, Rare Earth and Critical Minerals project, or CORE-CM. The new findings will form the basis for a grant request of an additional $9.4 million in federal funding to continue the research.

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

“When we talk about them as ‘critical minerals,’ a lot of the criticality is related to the supply chain and the processing,” said Michael Free, a professor of metallurgical engineering and the principal investigator on the DOE grant. “This project is designed around looking at some alternative unconventional domestic sources for these materials.”

The U-led study was published last month in the journal Frontiers in Earth Science. Team members included graduate students Haley Coe, the lead author, and Diego Fernandez, a research professor who runs the lab that tested samples.

What Are Rare Earth Elements?

Despite the moniker, rare earth elements (REEs) are not rare in Earth’s crust, but they are rarely found in concentrations high enough to make mining them economical Nearly 90% of the global supply is processed in China, according to the Bipartisan Policy Center.

These metallic elements include the 15 within the lanthanide series as well as scandium (Sc) and yttrium (Y), all found in the third column of the Periodic Table.

These elements are usually found in their oxide forms. Because they exist in such low concentrations, these minerals are hard to separate from ores and from each other.

Rare earths hold special properties that make them essential ingredients in materials associated with high-tech applications.

“It’s really rooted in the kinds of compounds that you can form with these rare elements or these critical minerals that make them attractive and more efficient,” said Michael Free, a University of Utah professor of metallurgical engineering. “When you look at the rarer elements, neodymium (Nd) praseodymium (Pr) and dysprosium (Dy), they can be combined with other elements to form high-power magnets.”

Many lanthanide compounds are used in glass and catalysts, as well as magnets, superconductors, phosphors, lasers and luminescent materials. Rare earths also found in everyday technology, such televisions and smartphone screens, medical devices, auto- and fluid catalysts. Carbon-neutral energy technology, including wind turbines, solar panels, electric vehicles, rechargeable batteries and energy-efficient lighting, also require these elements.

“With turbine blades, for example, in a windmill to generate power, you want to use the higher powered magnets to make them more efficient. It basically helps us in some of this energy transition. It’s about energy efficiency, it’s about energy density for storage,” Free said. “There’s a lot of strategic kinds of things with some of these elements that are critical, that are used in high-end electronic devices and satellite technologies and defense applications.These kind of elements perform much better than the more common elements that we’re familiar with.”

The U.S. uses, on average, 8,300 metric tons of rare-earth oxides a year, according to the U.S. Geological Survey. The Mountain Pass mine in California’s Mojave Desert is the nation’s largest producer of rare earth elements, but most of its output is sent overseas for processing.

“The supply here is not very established in some cases. It was established to some extent, but then it got shipped overseas because we didn’t want to do the sourcing here. We didn’t want to open up new mines here,” Free said. “So that leaves us vulnerable for a lot of these higher-end technologies and the clean-energy technologies that we’re trying to get more into.