Hg2+ reduction and re-emission from simulated wet flue gas desulfurization liquors

In this study, considering that Hg2+ in wet flue gas desulfurization (FGD) systems can easily be reduced and then released into atmosphere, causing secondary pollution, the researches about Hg2+ reduction and Hg0 re-emission mechanism were carried out. The effects of several experimental parameters on the reduction were studied, including initial pH, temperature, and concentrations of Cl− and S(IV). Our experimental results indicated that Cl− had a restraining effect on the Hg2+ reduction and Hg0 re-emission, after 24 h reaction, only 20.5% of Hg2+ was reduced with 100 mM Cl− in simulated desulfurization solution. Cl− can slow Hg2+ reduction and Hg0 re-emissions dramatically through changing reaction mechanism, with formation of new intermediate: ClHgSO3−, which can decompose to Hg0, but much more slowly than Hg(SO3)22− or HgSO3. Simulating the conditions of the practical application (initial pH 5, T = 50 °C, S(IV) = 5 mM, Cl− = 100 mM), we also found that Ca2+, NO3−, F−, etc. all had obvious effects on reduction rates. Based on the material balance and characteristic of the reactants, the reduction emission mechanism of Hg2+ has been established, providing theoretical basis for industrial application of mercury control in wet FGD systems.