THE AQUEOUS REDUCTION OF DIVALENT MERCURY BY SULFITE

Divalent Hg is reduced by sulfite in aqueous solutions. The proposed mechanism involves the formation of an instable intermediate, HgSO3, which decomposes to produce Hg+ which in turn is rapidly reduced to Hg0. The overall rate of the reaction is inversely dependent on the concentration of sulfite. This reaction may influence the concentration of Hg in cloud- and rain-water by reducing water soluble Hg2+ to volatile Hg0. At low concentrations of SO2(g) (5-mu-g m-3, 25-degrees-C), the rate of the conversion of Hg(SO3)2(2-) to Hg0 becomes significant (> 1 % h-1) at pH < 5.5. At higher SO2 concentrations (500-mu-g m-3), the same rate is expected at pH < 4.5.