The Power of Plasma: Extracting REEs From Coal

As the world continues its transition to a highly tech-driven economy, the National Energy Technology Laboratory (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 become a new supplier of these vital materials.

REEs are a group of 17 chemical elements that are included in the periodic table, which represent the 15 elements of the lanthanide series, plus scandium and yttrium. The word “rare” in REEs does not stem from a scarcity of deposits; rather, it signifies that REEs are often found in low concentrations too small for economical extraction. REEs are necessary components of smart phones, cars, television screens, and defense technologies, as well as windmills and other green energy assets.

Although the United States is a substantial consumer on the world market for REEs, the Nation is at a historically low level when it comes to extracting and processing these highly valuable resources; the United States relies heavily on imports. As a result, NETL is leading research efforts at businesses and research organizations across the country to help the United States secure a domestic supply of REEs from its own energy reserves and eventually supply the global market.

One of the country’s most important power resources, coal, could become an abundant and easily accessible domestic REE source. Appalachia’s coal, along with fly ash and acid mine drainage, contains recoverable REEs. To date, hydrophobic-hydrophilic separation and acid leaching processes have successfully extracted REEs, and NETL remains committed to exploring all available methods.

“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,” said NETL’s Federal Project Manager Jason Hissam. “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 heating a gas with a high enough temperature that gas molecules are ionized. During the past century, thermal plasma treatment was used in torch welding/cutting, spray coating, metal synthesis, extractive metallurgy, refining metallurgy, hazardous waste destruction, and more.

The collaborators researched the use of low-temperature plasma to pretreat coal-based materials resourced from the West Kentucky No. 13 and Fire Clay mines located within the state of Kentucky. Surface area measurements showed that plasma treatment provided increased surface area and pore volume, which meant other processes would be more effective at recovering REEs. This novel technology, integrated with traditional leaching and extraction processes, demonstrated how 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. 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 rate of REEs using this method shows promise,” said Hissam. “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 refining this process and discovering how to it make economically attractive to industry.”