Nutshells, Tires Can Help Clean Up Mercury Emissions

Nutshells, Tires Can Help Clean Up Mercury Emissions

Researchers have devised a way to use old tires and pistachio shells to remove mercury emissions from power plants. Activated carbon adsorbents made from the tires and shells work as well as or better than current commercial products and might even be cheaper to produce, say researchers at the University of Illinois and the Illinois State Geological Survey.

"Mercury is a toxic pollutant that can enter rivers, lakes and the human food chain," said Massoud Rostam-Abadi, a chemical engineer and head of energy and environmental engineering at the Survey. "Coal-fired power plants are one of the largest ... sources of mercury emissions. With funding provided by EPRI (Electric Power Research Institute) and the Illinois Office of Solid Waste Research, we looked for materials that could effectively remove mercury from the combustion flue gases."

Adsorbents, not to be confused with absorbents, are solids or liquids that attract and retain solid, liquid, or gas molecules, atoms, or ions. (Absorbents are solids or liquids that soak up fluid molecules and distribute them throughout their bodies.)

In a collaborative research program, Rostam-Abadi and Scott Chen, another chemical engineer at the Survey, and their UI colleagues, prepared adsorbents from a variety of feedstocks, including Illinois high-sulfur coal, waste tires, and pistachio shells. The adsorbents were then evaluated for their effectiveness at removing two forms of mercury emissions -- elemental mercury and mercuric chloride -- from several different simulated combustion gas streams.

"We found that mercury removal was affected by both the properties of the adsorbent and the flue gas compositions," Rostam-Abadi said. "In one flue gas, the adsorbents were equally effective in removing both forms of mercury. In another flue gas, the tire and pistachio carbons had nearly five times larger capacity for the adsorption of mercuric chloride than their coal-derived counterpart."