Abstract
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 Hg2+(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 Hg2+ reduction but had negligible influence on the Hg2+ retention by the grained fraction of gypsum. Increasing in pH value resulted in higher Hg2+ reduction and over 46% of Hg2+ was found to be reduced into Hg0 at pH 5.0. Besides, increased slurry temperature also promoted the Hg2+ reduction and Hg0 re-emission as well as the Hg2+ retention efficiency by gypsum. Other factors including S (IV), Cl− and NO3− concentration was found to inhibit Hg2+ transformation into Hg0 but slightly promoted the Hg2+ retained in gypsum. Moreover, the addition of sodium sulfide (Na2S), 2,4,6-trimercaptotiazine, trisodium salt nonahydrate (TMT), and sodium dithiocarbamate (DTCR) prevented the Hg2+ reduction and precipitated out as insoluble HgS, Hg3(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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