Experimental Study on the Stability of the Mercuric Complexes in Wet Flue Gas Desulfurization Wastewater

This paper discussed the stability of ClHgSO3- complexes in desulfurization wastewater after it emitted from WFGD system. The results of experiments showed that the increase in temperature promotes ClHgSO3- complex decomposition which fitted the pseudo first-order kinetics principle, and the Ea value was calculated to 19.93 J/mol. The increase of H+ concentration in the solution stimulates the decomposition of ClHgSO3- complexes. The result of competitive reaction indicated that Ca2+ was easier to react with SO32- than Hg2+ to form CaSO3, which is slightly soluble and stimulated the decomposition of complexes. SO42- ions inhibit the forward reaction of ClHgSO3- decomposition and promote ORP value of wastewater, which avoid the formation of unstable HgSO3. It was also found that Hg2+ concentration was relatively low in wastewater, and decomposition reaction cannot be evaluated by ORP change. Moreover, ORP value and variation negligibly reflect the stability of complexes.