Process migration and transformation of mercury in simulated wet flue gas desulfurization slurry system
Wet flue gas desulfurization (WFGD) system has been increasingly recognized to be effective in Hg removal. But the generated secondary pollution due to Hg re-emission from desulfurization solutions or solid byproducts has received researchers’ attention. In this paper, the distribution of captured Hg 2+ (L) in the simulated WFGD slurry was studied as a function of various environmental factors. Experimental results indicated that the pH value had a strong effect on Hg 2+ reduction but had negligible influence on the Hg 2+ retention by the grained fraction of gypsum. Increasing in pH value resulted in higher Hg 2+ reduction and over 46% of Hg 2+ was found to be reduced into Hg 0 at pH 5.0. Besides, increased slurry temperature also promoted the Hg 2+ reduction and Hg 0 re-emission as well as the Hg 2+ retention efficiency by gypsum. Other factors including S (IV), Cl − and NO 3 − concentration was found to inhibit Hg 2+ transformation into Hg 0 but slightly promoted the Hg 2+ retained in gypsum. Moreover, the addition of sodium sulfide (Na 2 S), 2,4,6-trimercaptotiazine, trisodium salt nonahydrate (TMT), and sodium dithiocarbamate (DTCR) prevented the Hg 2+ reduction and precipitated out as insoluble HgS, Hg 3 (TMT) 2 and Hg(DTCR) 2 on gypsum. The findings presented in this study could provide theoretical basis for Hg removal in coal-fired power plants.
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