Engineering professor advocates mercury mitigation

Elisse Lorenc

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.

On average, a cement plant produces about 1 million tons of cement per year. With there being about 100 cement plants in the United States, 100 million tons of cement are produced per year. About 1.6 tons of feed is required to produce 1 ton of cement. When cement production facilities are going through that much material, even if the mercury is at low levels, there becomes a significant abundance of mercury in the atmosphere.

A vital issue Sikkema is concerned with is the adverse health affects pertaining to the exposure of mercury.

“At present, about 9,000 tons of mercury are emitted into the atmosphere annually. Surprisingly, approximately 6,000 tons are from natural sources, such as volcanoes, soil and water surfaces, weathering processes of Earth crust and forest fires,” Sikkema said.

Mercury is a known neurotoxin — it causes threats for women during pregnancy, especially if the infant is within the early stages of growth, specifically with brain development.

If the mercury is exposed to the oceans where it can be absorbed from plants and sediments, fish can consume those harmful traces of mercury. When people eat those fish, they’re being exposed to harmful exposures of mercury.

“If it contaminates drinking water, it can cause kidney damage if ingested,” Ong said.

“It all depends on the concentration. Mercury is something that can accumulate in your body, as you are exposed to it, it accumulates,” he said. “If you take too much of mercury, there can be severe health affects, such as damage to hearing and speech.”

Another probing issue is the cost of equipment necessary to filter the mercury and the negative effects it would entail to foreign contributors of cement.

“The expense to install and operate this additional equipment will increase the costs to produce cement within the United States,” Sikkema said. “Instead of purchasing American-made cement, companies may shift purchases to cheaper imported cement [primarily from China]. In the countries where this imported cement is produced, environmental regulations are much more lax or nonexistent, such as mercury and other hazardous air pollutants. In addition, these plants tend to be less energy efficient, thereby increasing fossil fuel use.” 

One approach for the EPA is investigating is an environmental tariff. This would tax imported cement from countries lacking regulations similar to the United States. Essentially, the tax would make foreign cement more expensive than U.S.-made cement.

With the demand for cement to produce things such as concrete, Sikkema hopes to eventually work on more cost efficient technology that not only produces cement but emits less mercury.

“You want the plant to remain as efficient as possible because cement plants use an incredible amount of energy, so you don’t want the technology you’ve developed to be a big energy hog,” he said.

“I like projects that are rather broad in scope, it’s not just trying to do an engineering problem specifically, you have to look into the economics side to try and figure out what sort of technologies are cost efficient,” Sikkema said. “You have to look at the health risks and aspects to say, ‘OK, is this sort of thing appropriate to do, is it the best way to reduce negative health impacts to the population or would it be better to regulate different sorts of emissions.’ I think I like that there’s a lot of different, interesting problems within it.”