Engineering professor advocates mercury mitigation

Mercury is one toxin emitted from cement plants the Environmental Protection Agency and some ISU students and faculty strive to mitigate.

Say Ong, professor in civil, construction and environmental engineering, advocates the concerns of mercury emissions.

"Mercury is emitted from power plants," Ong said. "A large portion of it is from power plants and so [the EPA is] going down the line to look at different manufacturing facilities and see the emissions. They have a goal in terms of how much they want to reduce in terms on mercury in the environment. The question is how much are you going to reduce for each industry?"

EPA makes its regulations based on the maximum achievable control technology.

"In cement, they never really had any technologies like that and emissions are only based on the natural levels that were coming in," said Joel Sikkema, graduate in civil, construction and environmental engineering. "The emissions achieved by these plants are naturally low in mercury concentration. Once you can make that MACT standard, then everybody has to follow it and achieve it somehow."

Sikkema researches within the plants and observes how mercury concentrates within the plant over a period of time, what would trigger changes of concentration and spikes in emission levels and what materials have the highest concentration in mercury.

What's important is "looking at how mercury desorbs from the materials and reabsorbs in the cool areas, then exploit the loop to achieve control at a lower cost and hopefully develop a more cost efficient technology then what's available currently," Sikkema said.

Cement is a powder mixture consisting about 85 percent of limestone, which contains small traces of mercury.

"The average amount of mercury in limestone is 20 parts per billion," Sikkema said. "Mercury is a naturally occurring element usually it's in the form of mercury sulfide, naturally in limestone."

Cement has other additives, such as sand and iron ore. The additives are crushed with the limestone into a fine powder, which is run through a tunnel process where it's burned in a kiln. This process produces clinkers — an unprocessed cement by the large balls that are formed. The clinkers are then taken and crushed which is what makes the cement powder, Ong said.

Mercury is in the fuel for the kiln, which burns the limestone and other elements into cement. The fuel typically is coal, as it is widely available and cheap.

"The mercury in your coal is at low levels, but because they go through so much of it, it ends up being significant in terms of overall emissions from the plant," Sikkema said.