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-(L)(2+) 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 Hg-0 at pH 5.0. Besides, increased slurry temperature also promoted the Hg2+ reduction and Hg-0 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 Hg-0 but slightly promoted the Hg2+ retained in gypsum. Moreover, the addition of sodium sulfide (Na2S), 2,4,6trimercaptotiazine, trisodium salt nonahydrate (TMT), and sodium dithiocarbamate (DTCR) prevented the Hg2+ 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. (C) 2014 Elsevier Ltd. All rights reserved.