Gas phase oxidation and catalytic oxidation of element mercury (Hg-0) to bivalent mercury (Hg2+) were proposed to improve the mercury removal efficiency in the wet flue gas desulfurization (WFGD) system. However, the re-emission of Hg-0, generated by the reduction of absorbed Hg2+, would lead to a damping of the total mercury removal efficiency. In this paper, the absorption and reduction behaviors of bivalent mercury in the Ca-based WFGD slurry were evaluated in our purpose-built device. According to our experimental results, the slurry chemistry (such as CaSO3 content, SO42-, Cl- and pH value) had a strong influence on the reduction of absorbed bivalent mercury. And the inlet concentrations of SO2 and O-2 contribute little to the mercury absorption. Within the typical pH value range of 4.5-5.5, about 70% of inlet bivalent mercury was converted to Hg-0. The re-emission of Hg would be greatly retarded with the increase of [SO42-] due to the formation of HgSO4 or Hg3O2SO4. Moreover, it was found that Cl- would also inhibit the reduction of bivalent mercury through the ligands reactions between Cl- and Hg2+. (C) 2010 Elsevier B.V. All rights reserved.