William and Mary professor discusses acid mine drainage research

Caroline Fassett and Reed Widdoes, News Editor, Staff Writer

Stephanie DeSisto, a visiting assistant professor of geology at the College of William and Mary, visited the University on April 22 to discuss the research she conducted in Nova Scotia, Canada, which is detailed more fully in her article entitled Influence of hardpan layers on arsenic mobility in historical gold mine tailings.” The discussion explored the methods by which mines can remediate arsenic-rich gold waste, focusing on the back-end of dealing with the mining process and waste control.

DeSisto explained that Nova Scotia has a history in gold mining, experiencing lucrative peaks throughout the 19th and 20th centuries. Yet new minerals have formed in these areas, which have since been susceptible to mine waste. DeSisto said that these minerals “are important because they happen to be able to retain a significant amount of arsenic,” a chemical element which, in Nova Scotia, contaminates groundwater and contributes to mine waste.

Humans actually reside about “100 to 200 feet” near the mine waste; with wind, the toxicity presented by the waste can be easily picked up and carried into the vicinity of neighborhoods and homes.

“This is a human health concern, to be living so close to the mine waste like this,” DeSisto said.

DeSisto handed those in attendance small plastic bags with small colored index cards inside labeled with chemical formulas. DeSisto asked everyone to create chemical reactions using these index cards. They found that a combination of reactions creates a continuous loop of sulfide oxidation, illustrating the potential irreversibility of acid mine drainage. Acid mine drainage refers to the outflow of acidic water from metal or coal mines.

DeSisto that the five components that are needed for acid mine drainage to occur are sulfide minerals, oxygen, water, bacteria, and the absence of calcite. In conducting her research, DeSisto found that after placing a cover over the at-risk minerals, she can cut off their interaction with water and oxygen and thereby prevent or diminish acid mine drainage.

“These minerals want oxygen. They need oxygen if they’re going to remain stable and hold onto that arsenic,” DeSisto said.

Though DeSisto said that “sulfide minerals in the mine waste were still being oxidized” with the cover on, her results indicate that that the cover might still be the best solution in combating mine waste. Oxygen is still permeating the cover, which DeSisto said “isn’t good.” She said that the rest of the time “it appears that … the minerals with arsenic in them … aren’t releasing more arsenic.”

DeSisto outlined the difficulty in remediative strategies, saying that they should never make contamination issues worse and that the unusual nature of historical gold mine tailings makes an obvious remediation solution difficult. While DeSisto’s work at this particular site is complete, she will continue to conduct research at other sites.

“I liked the [index card] activity a lot. It helped me visualize [the chemical reaction process]. I’ve never taken chemistry before,” Isabelle Bristol ’16 said.

“I think just knowing the broader significance of the study was really interesting. And often with research projects in general we get so focused in on what it means in terms of that particular study, but applying it to a world scope was really interesting,” Emily DeLuca ’17 said.

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