The renewable energy industry heavily depends on rare earth elements, creating a need for increased resource development and production. However, the U.S. relies almost entirely on imports, with about 75% of these elements coming from China, which presents risks amid complex supply chains and geopolitical tensions.
Recent research suggests that the U.S. could have up to 11 million tons of rare earth elements in coal ash—residues from burned coal—representing nearly eight times the current domestic reserves.
This new research, led by the University of Texas at Austin, shows that the national coal ash supply contains enough rare earth elements to bolster the national supply without any significant new mining.
Co-lead author Bridget Scanlon, a research professor at UT’s Bureau of Economic Geology at the Jackson School of Geosciences, said, “This really exemplifies the ‘trash to treasure’ mantra. We’re trying to close the cycle, use waste, and recover resources in the waste while at the same time reducing environmental impacts.”
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This is the first study to count the national coal ash resources. It suggests that coal ash contains almost $8.4 billion worth of rare earth elements.
Although the concentration of rare earth elements in coal ash is lower than in geological deposits, its large-scale availability makes it a valuable resource. Coal ash is abundant across the U.S., and since the initial extraction process (mineral host removal) is already done, it offers a significant advantage.
Research shows that about 70% of the coal ash produced between 1985 and 2021—approximately 1,873 million tons—could be recovered. Much of this ash is stored in landfills, ponds, and offsite areas, while the remainder has been used in industries like cement production and road construction.
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The concentration of rare earth elements in coal ash varies based on its origin, which also impacts how much can be extracted. For example, coal ash from the Appalachian Basin has the highest concentration of rare earth elements, averaging 431 milligrams per kilogram, but only 30% of these elements can be extracted.
On the other hand, coal from the Powder River Basin contains a lower average concentration of 264 milligrams per kilogram, yet it has a higher extractability rate of about 70%. Much of the extraction work is still in the research stage. Bagdonas is involved in a pilot project at the National Energy Technology Lab focused on extracting rare earth elements from Powder River Basin coal ash.
Scanlon said that the foundational data provided in this study can help with building a broader market for coal ash as a resource.
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“This kind of broad reconnaissance-level analysis has never been done,” Scanlon said. “It provides a foundation for others to go into more detail.”
Chris Young, the chief strategy officer at Element USA, a company that extracts critical minerals from mineral and metallic waste, said the study underscores the great potential of coal ash as a resource. The industry’s challenge now is developing the workforce and operations needed to extract rare earth elements and other materials from coal ash and other mining byproducts.
“The idea of getting rare earth elements out of tailings (mining by-products) just makes a lot of sense. It’s a common-sense approach. The challenge is to convert that common-sense approach to an economic approach.”
Journal Reference:
- Reedy, R.C., Scanlon, B.R., Bagdonas, D.A. et al. Coal ash resources and potential for rare earth element production in the United States. Int J Coal Sci Technol 11, 74 (2024). DOI: 10.1007/s40789-024-00710-z