Laboratory investigation of Hg release from flue gas desulfurization products

Flue gas desulfurization (FGD) is a process applied to remove acid deposition precursors from the coal combustion air stream. This process also removes mercury (Hg) resulting in accumulation of this element in FGD produced solids. This project investigated Hg release from FGD materials to the air and water. Hg concentrations in the synthetic leaching precipitation procedure extracts, designed to simulate rainwater pH conditions, were in general <10 ng L(-1). Unlike coal fly ash, which has been found to adsorb Hg from the air, FGD materials were found to release Hg to the air over time with the addition of water a dominant environmental factor promoting release. The chemistry of the atmosphere to which the FGD materials were exposed (i.e., air Hg concentration and presence of oxidants), as well as that of the material (i.e., salts removed), was found to influence the magnitude of emissions. Although this work showed a component of the Hg captured by the FGD process could be released to the air under laboratory conditions, the potential for release under disposal and beneficial use conditions needs to be determined.