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 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.

► Both sulfate and chloride had inhibition effects on Hg2+ reduction.
► The formation of HgSO3SO42- was the main reason for reduction inhibition by sulfate.
► The Cl2HgSO32− was the main cause of reduction inhibition with chloride, rather than Cl2HgSO3-.
► The key step of Hg2+ is the decomposition of HgSO3.