West Virginia University (WVU) researchers are opening a new facility to capture rare earth elements (REEs) from acid mine drainage (AMD) from coal mining.

Through a collaborative research and development program with the US Department of Energy (DOE) National Energy Technology Laboratory (NETL), WVU is opening the Rare Earth Extraction Facility to bolster domestic supplies of rare earths, reduce the environmental impact of coal-mining operations, reduce production costs and increase efficiency for processing market-ready rare earths.

WVU is partnering with Rockwell Automation to facilitate market readiness through use of their sensor and control technologies in the new WVU facility.

The facility is the researchers’ phase-two project, worth $3.38 million, funded by NETL with substantial matching funding from WVU’s private sector partners. It follows on an earlier, phase-one project, worth $937,000, to study acid mine drainage as feedstock for rare-earth extraction. The goal of the pilot facility is to test the technical and economic feasibility of scaling-up the technology to commercialize the separation and extraction process.

In addition, the team will be working to define a US-based supply chain including the sludges created during acid mine drainage treatment and upstream to the acid-mine drainage source.

Conventional rare-earth recovery methods require an expensive, difficult and messy extraction process that generates large volumes of contaminated waste. China has been able to provide a low-cost supply of rare earths using these methods, and therefore, dominates the global market.

The conventional mining and extraction processes require mining ore from mineral deposits in rock, which is crushed into a powder, dissolved in chemical solutions and filtered. The process is repeated multiple times to retrieve rare earth oxides. Additional processing and refining separates the oxides from their tight bonds and further groups them into light rare earths and heavy rare earths.

Paul Ziemkiewicz, director of the West Virginia Water Research Institute and principal investigator on the project, is an expert in acid mine drainage. He found that acid mine drainage, a byproduct of coal mining, “naturally” concentrates rare earths. Active coal mines, and in many cases state agencies, are required to treat the waste, which in turn, yields solids that are enriched in rare earth elements.

Acid mine drainage from abandoned mines is the biggest industrial pollution source in Appalachian streams, and it turns out that these huge volumes of waste are essentially pre-processed and serve as good rare earth feedstock. Coal contains all of the rare earth elements, but it has a substantial amount of the heavy rare earths that are particularly valuable.

—Paul Ziemkiewicz

Studies show that the Appalachian basin could produce 800 tons of rare earth elements per year—approximately the amount the defense industry would need.

Conceptual Process Flowsheet

Two-step process. Ziemkiewicz, Xingbo Liu, professor of mechanical engineering in the Statler College of Engineering and Mineral Resources, and Aaron Noble, associate professor of mining and minerals engineering at Virginia Tech, have designed the processing facility from the ground up using advanced separation technologies. Chris Vass, a WVU graduate student and Summersville, West Virginia, native is the operator of the new facility.

The researchers are using a two-step process to separate the rare earths from acid mine drainage: acid leaching and solvent extraction, which they call ALSX.

Researchers will dissolve the sludge in an acid. That solution will then be transferred to glass mixers and settlers that will make an emulsion that allows the oil phase and its extractant chemical to grab rare earths from the water, leaving the non-rare earth base metals like iron in the water.

When that process is completed, the rare-earth-laden organic liquid enters another series of mixers and settlers that will strip the rare earths out as a concentrated solution and precipitate the rare earths as a solid, creating a concentrated rare earth oxide that can then be refined and further concentrated into pure rare earth metals to supply the metal refining industry.

The goal of the project is to produce three grams of rare earth concentrate per hour.

Scandium, one of these rare earths, is worth about $4,500 per kilogram as an oxide, the form that it will leave the facility, Anderson said. After refining, it would be worth $15,000 per kilogram.

Unused materials will be returned to the acid mine drainage treatment plant’s disposal system, resulting in a negligible environmental footprint.

A team, led by John Adams, assistant director of business operations at the WVU Energy Institute, is also defining the supply chain, moving upstream to the source and working with coal-industry partners. By producing a purified product at the mine, researchers could reduce transportation and waste handling costs.

Resources

• Paul Ziemkiewicz, Xingbo Liu, Aaron Noble (2018) “Extraction of rare earth elements from acid mine drainage precipitates”