15th December 2024

Huge cache of rare-earth elements found in U.S.

Coal ash from U.S. power plants may contain up to 11 million tons of rare-earth elements – eight times the nation's current domestic reserves, according to a new study.

Coal ash – the chalky remnants of coal burned for fuel – has been piling up across the United States for decades. But new research indicates that this material, long regarded as waste, could, in fact, be astonishingly valuable. The University of Texas at Austin (UTA) has found that the national coal ash supply contains enough rare-earth elements to significantly bolster the national supply without any new mining.

"This really exemplifies the 'trash to treasure' mantra," said Bridget Scanlon, a senior research scientist at UTA's Bureau of Economic Geology and co-lead author of a study published in the International Journal of Coal Science & Technology. "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 are a group of 17 elements that are essential for modern technology. They are also necessary for the transition to clean energy, being used in solar panels, batteries, magnets, and other applications.

Currently, however, the United States relies heavily on imports for its rare-earth element supply. About 70% come from China – posing serious challenges in a world of complex supply chains and geopolitical tensions.

The new research estimates there could be 11 million tons of rare-earth elements in accessible coal ash within the United States, which is nearly eight times the amount that the U.S. currently has in domestic reserves. The study is the first ever to tally up national coal ash resources.

"There's huge volumes of this stuff all over the country," said co-author Davin Bagdonas, a research scientist at the University of Wyoming. "And the upfront process of extracting the mineral host is already taken care of for us."

The researchers found that 70% of the coal ash produced from 1985 to 2021 – about 1.9 billion tons – is potentially recoverable, with the material stored in landfills, ponds, and other offsite areas. The rest of the ash has been sold and used by other industries like cement production and road construction.

Coal ash contains different levels of rare-earth elements depending on where it originates. The source location 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-earths, with an average 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 value at 264 milligrams per kilogram, but it has an extractability of about 70%.

A pilot project of the National Energy Technology Lab is currently underway to extract rare-earth elements from Powder River coal ash. The foundational data provided in this study can help with establishing a broader market for coal ash as a resource, according to Scanlon.

"This kind of broad reconnaissance-level analysis has never been done," she 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 materials from mineral and metallic waste, said that the new research underscores the great potential of coal ash as a resource. The challenge now for industry 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," he said. "The challenge is to convert that common-sense approach to an economic approach."

To that end, Element USA is in the process of moving its analytical lab and pilot equipment to Austin to leverage the mineral expertise at The University of Texas at Austin and offer critical mineral experience to students interested in critical mineral research and careers.

"We're excited about building that relationship with The University of Texas around mineral processing and mineral separation," Young said.

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