This paper studied the effects of sulfate and chloride ions on bivalent mercury (Hg2+) absorption and reduction behaviors in a simulated WFGD system. The aqueous mercuric ion-sulfite system reduction behaviors were monitored and investigated using a UV-visible spectrum. Thereafter, the mechanism of Hg2+ reduction in the presence of sulfate and chloride ions was proposed. Experimental results revealed that both sulfate and chloride ions had inhibition effects on aqueous Hg2+ reduction to Hg-0. The inhibition was assumed due to the formation of HgSO3SO42- (in the presence of SO42-) and ClHgSO3-/Cl2HgSO32- (in the presence of Cl-). And it was found that Cl2HgSO32- complex was more stable than ClHgSO3- in excess of Cl-. The formation of the above-mentioned complexes in the presence of SO42- and Cl- would damp the formation of HgSO3, whose decomposition was assumed to be the key step of Hg2+ reduction. (c) 2011 Elsevier Ltd. All rights reserved.