Characterization of Hg0 re-emission and Hg2 + leaching potential from flue gas desulfurization (FGD) gypsum

Flue gas desulfurization system used for SO2 removal has co-beneficial removal of Hg, which has resulted in Hg-laden gypsums. With growing beneficial reuse applications of the FGD gypsum, it has been recognized as a potential source of Hg pollution. In this paper, the fate and mobility of Hg were investigated. The Hg content in four samples varied widely and it showed a significant correlation between Hg and sulfite contents in gypsum. In leachate, Hg concentration varied during the leaching process. The Hg extraction rate generally increased with decreasing pH value, which suggested that the environmental risk of FGD gypsum increased during the multipurpose utilization processes, resulted from severe acid rain. The released Hg from FGD gypsum used in this study exhibited biphasic kinetics. Hg in FGD gypsum samples not only appeared in the leachate but also re-emitted into the air. The Hg reduction kinetics followed the pseudo-first-order kinetic model well. Our results provide the theoretical understanding for the co-removal of highly soluble oxidized Hg in WFGD systems and also in the recycling of the FGD gypsum.