A mechanism study of chloride and sulfate effects on Hg2+ reduction in sulfite solution

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 Hg0. The inhibition was assumed due to the formation of HgSO 3 SO 4 2 - (in the presence of SO 4 2 - ) and ClHgSO 3 - / Cl 2 HgSO 3 2 - (in the presence of Cl−). And it was found that Cl 2 HgSO 3 2 - complex was more stable than ClHgSO 3 - in excess of Cl−. The formation of the above-mentioned complexes in the presence of SO 4 2 - and Cl− would damp the formation of HgSO3, whose decomposition was assumed to be the key step of Hg2+ reduction.