By University of Texas at Austin
March 17, 2025

Coal ash in the U.S. holds substantial rare earth elements, potentially reducing dependence on imports, with ongoing research and pilot projects working to make extraction economically viable.

Coal ash, the powdery residue left after burning coal for fuel, has accumulated across the United States for decades. New research from the University of Texas at Austin reveals that this vast supply contains enough rare earth elements to significantly strengthen the nation’s reserves without the need for additional mining.

“This really exemplifies the ‘trash to treasure’ mantra,” said co-lead author Bridget Scanlon, a research professor at UT’s Bureau of Economic Geology at the Jackson School of Geosciences. “We’re basically trying to close the cycle and use waste and recover resources in the waste, while at the same time reducing environmental impacts.”

Rare earth elements, a group of 17 critical materials, are essential for modern technology and the transition to lower-carbon energy. They are key components in solar panels, batteries, magnets, and other advanced energy technologies.

Currently, the United States depends almost entirely on imports for its rare earth supply, with about 75% coming from China. This reliance raises concerns due to global supply chain complexities and geopolitical tensions.
A Vast, Untapped Domestic Resource

The new research found that there could be as much as 11 million tons of rare earth elements in accessible coal ash in the United States, which is nearly 8 times the amount that the U.S. currently has in domestic reserves, according to the researchers.

The results were published in the International Journal of Coal Science & Technology. The U.S. Department of Energy is also applying the study’s methodology to conduct its own national assessment of coal ash resources.

Even though the level of rare earth elements in coal ash is relatively low when compared with those mined from geological deposits, the fact that the ash is readily available in large quantities makes it an attractive resource, said co-author Davin Bagdonas, a research scientist at the University of Wyoming.

“There’s huge volumes of this stuff all over the country,” Bagdonas said. “And the upfront process of extracting the (mineral host) is already taken care of for us.”

The researchers found that about 70% of the coal ash produced from 1985 to 2021 — a total of about 1,873 million tons — is potentially recoverable, with the material stored in landfills, ponds, and offsite storage areas. The rest of the coal ash has been sold and used by other industries, such as cement production and road construction.
Regional Differences in Rare Earth Element Content

Coal ash contains different levels of rare earth elements depending on where it originates. Place of origin also affects how much of the rare earth elements can be extracted.

For example, ashes from Appalachian Basin coal contain the highest amounts of rare earth elements, with an average value of 431 milligrams per kilogram. But only 30% of the rare earth elements it contains can be extracted. In contrast, coal from the Powder River Basin has the lowest average value of rare earth elements at 264 milligrams per kilogram, but it has an extractability of about 70%.