Concentrations are highest in coal from the Appalachian Mountains
A study of the content of rare earth elements in U.S. coal ashes shows that coal mined from the Appalachian Mountains could be the proverbial golden goose for hard-to-find materials critical to clean energy and other emerging technologies.
In the wake of a 2014 coal ash spill into North Carolina’s Dan River from a ruptured Duke Energy drainage pipe, the question of what to do with the nation’s aging retention ponds and future coal ash waste has been a highly contested topic.
One particularly entrepreneurial idea is to extract so-called “critical” rare earth elements such as neodymium, europium, terbium, dysprosium, yttrium and erbium from the burned coal. The Department of Energy has identified these globally scarce metals as a priority for their uses in clean energy and other emerging technologies. But exactly how much of these elements are contained in different sources of coal ash in the U.S. had never been explored.
Researchers from Duke University measured the content of rare earth elements in samples of coal ash representing every major coal source in the United States. They also looked at how much of these elements could be extracted from ash using a common industrial technique.
The results, published online May 26 in the journal Environmental Science and Technology, showed that coal from the Appalachian Mountains contains the most rare earth elements. However, if extraction technologies were cheap enough, there are plenty of rare earth elements to be found in other sources as well.
“The Department of Energy is investing $20 million into research on extraction technologies for coal wastes, and there is literally billions of dollars’ worth of rare earth elements contained in our nation’s coal ash,” said Heileen Hsu-Kim, the Mary Milus Yoh and Harold L. Yoh, Jr. Associate Professor of Civil and Environmental Engineering at Duke.
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