All That Glitters

By Carl Marzialli

“I was just running down the corridor. I went to Dr. Perez and said ‘It worked, it worked!’ I was very happy.”

All That Glitters

While burning one kind of fossil fuel, Nasrin Khalili had an idea for cleaning up another.

Khalili was in her car-with offices on Main CampusStuart School of Business, and Argonne National Laboratories, the associate professor of environmental management is often in her car-when a casual memory sparked a key insight.

Khalili had been looking for a way to remove more mercury, a toxic metal, from the exhaust gas of coal-burning power plants. She knew that mercury bonds easily to gold. She also knew that activated carbon-structurally modified charcoal-is used to capture particles and contaminants in many settings, from smokestacks to home filtration systems.

Then Khalili remembered that in an ancient Indian culture, craftsmen applied a gold layer to statues by mixing carbon and gold in a very fine paste, applying it to the statue, and removing the carbon with heat. Khalili asked herself: What if, instead of plating the statue, the gold stuck to the carbon? And what if the gold-plated carbon formed a porous filter for power plant emissions, trapping mercury vapor but letting other gases flow through?

Khalili does not spend much time pondering “what if’s.” She formed a project team with graduate students and Victor Perez-Luna, assistant professor in chemical and environmental engineering. The researchers decided the idea had potential. There was one problem: There was no such thing as gold-plated carbon.

Now there is. Last June Khalili’s team filed for a patent to protect a novel process for manipulating the structure of activated carbon and plating its pores with gold in minimal, inexpensive and controllable amounts.

Because the patent is pending, Khalili will not discuss details of the process, except to say that gold plating became possible once the team discovered a way to modify the surface of the carbon pores.

The memory of the breakthrough makes her light up.

“Oh God, oh God, you have to see me that day,” she says. “Because we were trying and nothing was happening, basically.”

The team had experimented with one method after another. Then a graduate student of Khalili’s walked into her office on Main Campus, and announced that their numerous attempts had finally hit the proverbial goldmine. Says Khalili: “I was just running down the corridor. I went to Dr. Perez and said ‘It worked, it worked!’ I was very happy.”

Khalili’s team had created a material that, used as a filter, removes nearly 100 percent of mercury from gas emissions. She says the process uses less than a third of the carbon, by weight, of existing mercury removal methods. Those methods have a maximum efficiency of about 98 percent, says Khalili.

“We are aiming for zero emission,” she says.

Because the gold is plated in a very thin layer, its cost is almost negligible. As a bonus, the filter can be recycled, and the trapped mercury recovered for use in other industrial processes.

“Suddenly, because of the specific structure, low cost, high efficiency, we applied for the patent and within one month the lawyer said, ‘There’s nothing such as this on the market.’” Khalili’s team has begun pilot scale testing of the process. The researchers are applying for grants from federal and state agencies to develop and evaluate the filter in true industrial conditions.

The stakes are significant. Mercury from coal-fired power plants accounts for 70 percent of total mercury air pollution. Despite modern scrubbing methods, coal power plants release over 86,000 pounds of mercury every year. The metal accumulates in the food chain. Elevated levels can damage the central nervous system in humans, and has even been linked to autism. The Environmental Protection Agency has identified mercury as the air pollutant of “greatest potential concern” to the environment and human health, and lawsuits have been filed against utilities because of it.

Mercury has even been linked to autism, and lawsuits have been filed against utilities. Asked to comment on the technical issues of mercury removal, neither Illinois’ Exelon utility nor Wisconsin Energy Corporation provided spokespersons.

Khalili hopes that what the utilities avoid publicly, they will embrace privately. She dreams of a future where no smokestack will be without a gold-carbon filter.
And if that dream is shattered, she has another application in mind: removal of copper from tequila.

But who wants their tequila less toxic?

Better stick with power plants.