Mercury in Illinois Coals: Abundance, Forms, and Environmental Effects

Abstract

Coal databases of the Illinois State Geological Survey and United States Geological Survey were analyzed to better understand the occurrence and potential for environmental release of mercury (Hg) from Illinois and other U.S. coals. The Hg content of in-ground Illinois coal samples varies from 0.036 to 0.632 mg/kg with an average of 0.16 mg/kg (or 6.4 mg/10⁶ Btu). Mercury appears to be associated mostly with pyrite in Illinois coals. On average, conventional physical cleaning of in-ground Illinois coals removes 47% of the original Hg, resulting in an average Hg concentration of 3.1 mg/10⁶ Btu in marketed Illinois coals. With advanced physical cleaning of Illinois coals, the average Hg removal rate can exceed 80%. Furthermore, Hg in the flue gas from combusting Illinois coals is largely Hg²⁺ , most of which can be captured by lime or limestone scrubbers. In contrast, marketed coals from the largest U.S. producing basin, the Powder River Basin, have an average Hg concentration of 5.7 mg/10⁶ Btu and combusting these coals apparently emits Hg mostly as Hg° , which is not easily captured by scrubbers during combustion.