Cleaning Waste With Waste

Pitt researchers use industrial waste to develop “no-nonsense approach” to meeting new EPA mercury emissions standards

On March 15, the Environmental Protection Agency issued the Clean Air Mercury Rule, the first regulation to permanently cap and reduce mercury emissions from coal-fired power plants. The next day, at the 229th American Chemical Society National Meeting in San Diego, Pitt researchers presented a new method of cleaning up such emissions using a common industrial waste product as a resource.

Mercury, a neurotoxin, is emitted in the coal-burning process and can travel for miles through the air. Current mercury-cleanup technologies are based on injecting powdered activated carbon to adsorb the mercury and then storing the loaded carbon together with fly ash in the ashing ponds. Pitt professor of civil and environmental engineering Radisav Vidic and graduate student Wenguo Feng were concerned that this method would not permanently sequester the mercury. Although the technique’s effectiveness has been studied, “the problem is that most of that work is done over a short period of time,” said Vidic. “This mercury is going to sit in the ashing pond for decades and over time will just accumulate. Our concern is that it may not stay there.”

Observing that mercury exists in nature as the stable compound mercuric sulfide, or cinnabar, Vidic and Feng decided to impregnate the activated carbon with sulfur to improve its ability to sequester mercury. “These sulfur-impregnated sorbents have an enormous capacity for mercury, much higher than the raw activated carbon,” said Vidic.

Next, they found that the surface of activated carbon can be used to capture hydrogen sulfide, a waste product from many industrial processes—petroleum refining, natural gas cleanup, and coke ovens, for example (“the stinky stuff,” Vidic called it)—in the form of elemental sulfur. Combining these two processes, the researchers are able to use one industrial waste product to clean up the other.

The researchers are currently investigating how to modify the hydrogen sulfide and activated carbon to be reactive toward mercury. “We hope through this project to gain additional fundamental understanding of the removal of pollutants using adsorption technology,” said Feng.
Vidic described his team’s method as “a no-nonsense approach that will provide a long-term solution to the problem.” However, he said, “It’s going to require understanding on the part of regulators, utilities, the scientific community, and the public to get behind it and solve this problem once and for all so our children will have a better environment to live in.” • Karen Hoffman