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The Power of Plasma: Extracting REEs From Coal

As the world continues its transition to a highly tech-driven economy, NETL supports innovative techniques to develop a reliable domestic supply of rare earth elements (REEs), which are vital materials for modern technologies. To that end, NETL is collaborating with the University of Kentucky and their subcontractor Virginia Tech to demonstrate a novel process that could see America’s coal country as a new supplier of these vital materials.

REEs, which represent the 15 elements of the lanthanide series plus scandium and yttrium, are used in the manufacture of smart phones, cars, television screens and defense technologies; even windmills and other green energy equipment need these resources to function.

The “rare” in rare earth elements stem not from a scarcity of deposits, but rather, in their sparse concentrations. However, one of the country’s historic power sources, coal, could become an abundant and easily accessible domestic REE source.

The United States is at a historically low level in extracting and processing these highly valuable resources yet is a substantial consumer of the world market for REEs. NETL has been leader and financial supporter of research efforts at businesses and research organizations around the country with the goal of not only securing a domestic supply from the nation’s own energy reserves but also to supply the global market.

Appalachia’s coal, along with fly ash and acid mine drainage, contains recoverable REEs. Means of extracting them via hydrophobic-hydrophilic separation and acid leaching processes have shown some successes, and NETL remains committed to exploring all available avenues.

“While searching for a reliable supply of these vital elements, we need to research all viable technologies to determine which are the most efficient and cost-effective,” Jason Hissam, NETL federal project manager, said. “While we’ve seen several methods of extracting these resources from coal, the University of Kentucky’s low-temperature plasma research has been shown to be technically viable.”

Plasma, which is distinct from the liquid, gaseous and solid states of matter is formed by striking a gas with enough energy that gas molecules are ionized. During the past century, thermal plasma treatment saw applications in torch welding/cutting, spray coating, metal synthesis, extractive metallurgy, refining metallurgy, hazardous waste destruction and more.

The collaborators researched using low-temperature plasma to pretreat coal-based materials resourced from West Kentucky No. 13 and Fire Clay mines located within the state of Kentucky.  Surface area measurements found that plasma treatment provided increased surface area and pore volume which made other processes more effective at recovering REEs. This novel technology integrated with traditional leaching and extraction processes was demonstrated to effectively recover REEs from the coal samples.

Low-temperature plasma treatment was found to provide heavy REE leaching performance improvements on the low-density, higher carbon content fractions of the West Kentucky No. 13 coal, and high-temperature oxidation provided exceptionally high REE recovery for all fractions of both the Fire Clay and West Kentucky No. 13 coarse refuse materials.

“The higher recovery of rare earth elements using this method shows promise,” Hissam said. “It’s another potential tool at our disposal as we search for optimal ways to secure a reliable domestic supply of these crucial minerals. Moving forward, the challenge for NETL and its partners in academia is refinement and discovering how to make this process economically attractive by industry.”