Mercury is one of a number of pollutants (like dioxins) that persist in the environment and bioaccumulate in the food chain. Because of its toxicity and the potential for bioaccumulation, mercury emissions to the environment are the subject of environmental regulation. U.S. EPA estimates that 87% of the man-made emissions of mercury come from point sources of combustion. There are currently emission limits on mercury from certain categories of combustion sources, including cement kilns and incinerators burning hazardous waste. Cement kilns that do not burn hazardous waste are not subject to these emission standards. However, EPA is currently reviewing the need for emission standards for mercury and other pollutants from cement kilns. In this paper, we review the chemistry of mercury in the cement-making process and develop a simple model for understanding the distribution of mercury among various streams in different types of cement kilns.
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