These rare earth metals consist of the 17 chemically similar elements at the bottom of the periodic table, such as cerium and scandium. Despite their name, they’re not “rare” because they’re often found in other minerals, within the earth’s crust or, in this case, in coal and coal byproducts.
Yet the U.S. imports nearly all of its rare earth elements. China produces about 83 percent of the world’s rare earth elements used in modern technologies such as phones, batteries, TVs and medical and defense applications.
The reason the U.S. hasn't tapped into this market is because the processing of rare earths is considered cumbersome, costly and energy intensive. Conventional extraction efforts involve grinding through masses of rock and disturbing undeveloped land.
But in recent years, Ziemkiewicz identified the potential of extracting rare earths from acid mine drainage after he analyzed old data sets from the U.S. Geological Survey.
Acid mine drainage is the outflow of acidic water from a mine. Federal and state law requires that it be treated prior to discharge to a stream.
Ziemkiewicz noticed high concentrations of the metals coming out of the mines but none in the treated effluent, which is the water discharged to a stream. That meant that the rare earths are concentrated in the treatment sludge, which is the solid material from the raw acid mine drainage.
“In other words, we found a natural process for concentrating rare earth metals,” Ziemkiewicz said.
The U.S. currently has no active rare earth mines. So last year the Department of Energy’s National Energy Technology Laboratory solicited ideas for extracting these elements from coal and related byproducts. The WVU team focused on the solid residues left over after acidic coal mine drainage.
Obtaining rare earths this way eliminates any additional environmental risks and monetary costs that would occur with conventional extraction methods.
“The coal market may fluctuate over time, but acid mine drainage will be constant,” Ziemkiewicz said. “Long after mining is done, there will still be acid-generating coal mines. In fact, some of our richest rare earth concentrations have come from sites where mining ceased 30 years ago.”
Larger concentrations of rare earths are present in the northern and central Appalachian coalfields, which contain more acid mine drainage and are where WVU researchers are collecting samples.
Development of refining methods is under way at the labs of co-investigators Xingbo Liu and Aaron Noble, of the WVU Benjamin M. Statler College of Engineering and Mineral Resources.
“I see a future where abandoned mine sites could be acquired by commercial enterprises and managed as rare earth production facilities,” Ziemkiewicz said.
The goal of the current project is to identify what the processing costs would look like. WVU researchers are partnering with the U.S. Department of Energy National Energy Technology Laboratory, members of the coal industry and the West Virginia Department of Environmental Protection.
“The support we’ve received has been tremendous and if this all works out, we'll turn an environmental liability into an economic opportunity,” Ziemkiewicz said.
In West Virginia and Pennsylvania, it is estimated that acid mine drainage could produce more than 45,000 tons of total rare earth elements per year, or about three times the current U.S. demand.
Ziemkiewicz hopes his team’s research can ramp up U.S. involvement in the rare earths market. He believes it could help boost the economies of communities affected by the decline of coal.
“In many distressed communities where coal mines have shut down, you have acid mine drainage sites,” he said. “Some of these distressed towns could have rare earth extraction plants. Plus, you’re creating a domestic source for something that's otherwise imported. That creates better value for the nation and the consumer.”