Elisa D’Angelo built a wetland with powerful potential—a system that removes toxic elements that might leach out of coal slurry impoundments. 

“Our goal is to help the coal industry reduce liabilities associated with mining and coal preparation and help communities near the hundreds of coal slurry impoundments in the Appalachians,” said D’Angelo, Plant and Soil Sciences associate professor. 

To produce a cleaner-burning coal, companies must reduce ash and lower sulfur and mercury. The preparation process separates coarse refuge, similar to rocks, from smaller particles called fines. Coarse refuge is used to build dams that confine slurry containing the fines.

“Sometimes impoundments leak into natural water bodies,” D’Angelo said. “But little was known about the chemical composition, so it was impossible to know the potential impacts.”

D’Angelo, aided by Biosystems and Agricultural Engineering professor Richard Warner and Jason Unrine, Plant and Soil Sciences assistant professor, analyzed samples from slurry impoundment and compared the results to water quality criteria.

“Of the dozen trace elements we measured, only one element was potentially causing a problem,” D’Angelo said. “It was right above what they call the warm water aquatic habitat criteria.”

She designed a multi-stage wetland that focused on that element, selenium, as well as on several other elements that could pose a problem at other impoundments. 

Her pilot wetland consists of five stages, which use various natural materials, including wood chips, corncobs, and gravel, intended to remove each element in sequence. The first stage raises the pH. The second stage causes dissolved iron, arsenic, manganese, and selenium to fall out in a solid form and ultimately settle in the third stage.“When contaminants are dissolved, they tend to be more mobile in the environment and reactive with the human body. When converted to solid forms, they’re not as mobile or reactive,” D’Angelo explained.

The fourth and fifth stages, respectively, filter the remaining liquid through a gravel bed and reduce sulfate.

“What we found was, 96 percent of selenium was removed in just Stage 1,” D’Angelo said. “That was great news!”

D’Angelo’s next step is to sell the idea to the coal industry. “It could be a viable green technology for treating this class of waste.”

— Carol Lea Spence 

Photo by Matt Barton