Hg~0 Re-emission Reaction Pathways And Control From Wet Flue Gas Desulfuri-zation Liquors

In this study, considering that Hg²⁺ in wet flue gas desulfurization (FGD)systems can easily be reduced and then released into atmosphere, causing secondarypollution, the researches about Hg²⁺ reduction and Hg⁰ re-emission mechanism andrestrain ways were carried out.Simulating the conditions of the practical desulfurization solutions, the effects ofseveral experimental parameters on the reduction were studied, including initial pH,temperature, concentrations of Cl^-, S(â…£), Ca²⁺, Mg²⁺, F^-, etc. Our experimentalresults indicated that superfluous S(â…£) had a restraining effect on Hg²⁺ reduction byforming Hg(SO₃)₂^2-. Cl^- can slow Hg²⁺ reduction rate dramatically through changingreaction mechanism, with formation of new intermediate: ClHgSO₃^-, which candecompose to Hg⁰, but much more slowly than Hg(SO₃)₂^2- or HgSO₃.We also investigated stabilization of Hg²⁺ by comparing the comprehensivetreatment effects of several precipitating agents, including DTCR, TMT-18, Na₂S, etc.The results showed that removal effects of these precipitating agents are DTCR-2＞Na₂S＞DTCR-3＞DTCR-1＞TMT-18. DTCR-2 was found to be the most ideal one,whose removal efficiency can be reached to 90%.In addition, selected precipitating agents were proved to be effective to inhibitHg²⁺ reduction and Hg⁰ re-emission from FGD liquors, more than 90% Hg²⁺ wascaptured by precipitating agents and Hg²⁺ reduction efficiency was decreased to only3% or less.Based on the researches above, the mechanism and control methods of Hg²⁺reduction and Hg⁰ re-emission had been established, providing theoretical basis forindustrial application of mercury control in wet FGD systems.