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Abstract: The aqueous phase oxidation of gaseous elemental mercury (Hg0) by potassium persulfate (K2S2O8, KPS) catalyzed by Ag+ and Cu2+ was investigated using a glass bubble column reactor. Concentrations of gaseous Hg0 and aqueous Hg2+ were measured by cold vapor generation atomic absorption spectrometry (CVAAS). The effects of several experimental parameters on the oxidation were studied; these include different types of catalysts, pHs and concentrations of potassium persulfate, temperatures, Hg0 inlet concentrations and tertiary butanol (TBA). The results showed that the removal efficiency of Hg0 increased with increasing concentration of potassium persulfate and catalysts Ag+, Cu2+ and Ag+ provided better catalytic effect than Cu2+. For example, in the presence of 5.0mmoll−1 KPS, the mercury removal efficiency could reach 75.4 and 97.0% for an Ag+ concentration of 0.1 and 0.3mmoll−1, respectively, and 69.8 and 81.9% for 0.1 and 0.3mmoll−1 Cu2+. On the other hand, high temperature and the introduction of TBA negatively affect the oxidation. Furthermore, the removal efficiency of Hg0 was much greater in neutral solution than in either acidic or alkaline solution. But the influence of pH was almost eliminated upon the addition of Ag+ and Cu2+, and high Hg0 inlet concentration also has positive impact on the removal efficiency of Hg0. The possible catalytic oxidation mechanism of gaseous mercury by KPS was also proposed. [Copyright &y& Elsevier]

Abstract: Mercury (II) (Hg2+) ion can be reduced by aqueous S(IV) (sulfite and/or bisulfite) species, which leads to elemental mercury (Hg0) emissions in wet flue gas desulfurization (FGD) systems. Numerous reports have demonstrated the high trapping efficiency of sodium dithiocarbamate over heavy metals. In this paper, a novel sodium dithiocarbamate, DTCR, was utilized as a precipitator to control Hg2+ reduction and Hg0 emission against S(IV) in FGD solutions. Results indicated that Hg2+ reduction efficiency decreased dramatically while precipitation rate peaked at around 91.0% in consistence with the increment of DTCR dosage. Initial pH and temperature had great inhibitory effects on Hg2+ reduction: the Hg2+ removal rate gradually increased and reached a plateau along with the increment of temperature and initial pH value. Chloride played a key role in Hg2+ reduction and precipitation reactions. When Cl− concentration increased from 0 to 150mM, Hg2+ removal rate dropped from 93.84% to 86.05%, and the Hg2+ reduction rate remained at a low level (<7.8%). SO4 2−, NO3 − and other common metal ions would affect the efficiency of Hg2+ reduction and precipitation reactions in the simulated desulfurization solutions: Hg2+ removal rate could always be above 90%, while Hg2+ reduction rate was maintained at below 10%. The predominance of DTCR over aqueous S(IV), indicated by the results above, has wide industrial applications in FGD systems. [Copyright &y& Elsevier]

Abstract: 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 24h reaction, only 20.5% of Hg2+ was reduced with 100mM 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)2 2− or HgSO3. Simulating the conditions of the practical application (initial pH 5, T =50°C, S(IV)=5mM, Cl− =100mM), 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. [Copyright &y& Elsevier]