U.S. fly ash contains high amounts of rare earth elements, potentially reducing reliance on imports, and ongoing research and pilot projects are working to make mining economically viable. Coal ash, the powdery residue left after burning coal for fuel, has been accumulating across the United States for decades. New research from the University of Texas at Austin shows that this abundance of rare earth elements is sufficient to significantly enhance U.S. rare earth reserves without the need for additional mining.

Coal ash landfill in Shrewsbury, Massachusetts. Recent research from the University of Texas at Austin tallied possible rare earth elements found in coal ash from across the country. Image source: Massachusetts Department of Environmental Protection.

"This really exemplifies the 'waste to treasure' idea," said co-lead author Bridget Scanlon, a research professor at the Bureau of Economic Geology in the UT Jackson School of Geosciences. "We're basically trying to close the loop, utilize waste and recover resources from waste while reducing the impact on the environment."

Rare earth elements are made up of 17 key materials and are vital to modern technology and the transition to low-carbon energy. They are key components in solar panels, batteries, magnets and other advanced energy technologies.

Currently, the United States relies almost entirely on imports for rare earth supplies, about 75% of which comes from China. This dependence raises concerns due to the complexity of global supply chains and geopolitical tensions.

Researchers say new research has found that available coal ash in the United States may contain up to 11 million tons of rare earth elements, which is almost eight times the current domestic reserves of the United States.


Total amount of coal ash reported by the electric power sector and the amount of potentially available coal ash between 1985 and 2021. Source: Reedy et al.

This study is the first to count coal ash resources nationwide. Researchers estimate that $8.4 billion worth of rare earth elements could be extracted from available coal ash resources.

The findings were published in the International Journal of Coal Science and Technology. The U.S. Department of Energy is also applying the study's methods to assess the country's coal ash resources.

Although the content of rare earth elements in coal ash is relatively low compared to those mined from geological deposits, coal ash is an attractive resource because it is easily available in large quantities, said Davin Bagdonas, a research scientist at the University of Wyoming and co-author of the paper.

“There’s a lot of this ore all over the country,” Bagdonas said. “And we have already taken care of the preliminary mining (mineral body) process.”

The researchers found that about 70% of the coal ash generated between 1985 and 2021, totaling about 1.873 billion tons, was recyclable and the material was stored in landfills, ponds and off-site storage areas. The remaining coal ash has been sold and used in other industries such as cement production and road construction.

The content of rare earth elements in coal ash varies with its origin. Origin also affects the amount of rare earth elements extracted.

For example, Appalachian Basin coal ash has the highest concentration of rare earth elements, averaging 431 milligrams per kilogram. But only 30% of the rare earth elements can be extracted. In comparison, Powder River Basin coal ash has the lowest rare earth element content, averaging 264 milligrams per kilogram, but the extractability rate is about 70 percent.


Estimating the total amount of ash associated with U.S. coal production by basin. About 83% of all ash generated during this period came from the Appalachian, Powder River and Illinois basins. Source: Reedy et al.

Much of the work on rare earth element extraction is still in the research stage. Bagdonas is involved in a pilot project at the National Energy Technology Laboratory to extract rare earth elements from Powder River Basin coal ash.

Scanlon said the study provides fundamental data that can help build a broader market for coal ash resources.

"This extensive reconnaissance-level analysis has never been done," Scanlon said. "It lays the foundation for more detailed studies by others."

Chris Young, chief strategy officer at ElementUSA, a company that extracts critical minerals from mineral and metal waste, said the research highlights the huge potential of coal ash as a resource. The current challenge for the industry, he said, is developing the workforce and operations needed to extract rare earth elements and other materials from coal ash and other mining by-products.

"The idea of ​​extracting rare earth elements from tailings (mining by-products) makes a lot of sense. It's a common-sense approach," he said. “The challenge is to translate this common sense approach into an economic approach.”

To this end, ElementUSA is relocating its analytical laboratories and pilot facilities to Austin to leverage the mineral expertise at The University of Texas at Austin and provide critical minerals experience to students interested in critical minerals research and careers.

"We are excited to establish a relationship with the University of Texas in mineral processing and mineral separation," Young said.

Compiled from /ScitechDaily