title: Fate of mercury in flue gas desulfurization gypsum determined by Temperature Programmed Decomposition and Sequential Chemical Extraction.
abstract: A considerable amount of Hg is retained in flue gas desulfurization (FGD) gypsum from Wet Flue Gas Desulfurization (WFGD) systems. For this reason, it is important to determine the species of Hg in FGD gypsum not only to understand the mechanism of Hg removal by WFGD systems but also to determine the final fate of Hg when FGD gypsum is disposed. In this study, Temperature Programmed Decomposition (TPD) and Sequential Chemical Extraction (SCE) were applied to FGD gypsum to identify the Hg species in it. The FGD gypsum samples were collected from seven coal-fired power plants in China, with Hg concentrations ranging from 0.19 to 3.27μg/g. A series of pure Hg compounds were used as reference materials in TPD experiments and the results revealed that the decomposition temperatures of different Hg compounds increase in the order of Hg2Cl2<HgCl2<black HgS<Hg2SO4<red HgS<HgO<HgSO4. The Hg compounds existing in FGD gypsums identified by TPD included HgCl2, Hg2Cl2, Hg2SO4, black HgS and red HgS, of which mercury sulfides were the primary compounds. The results of SCE indicated that Hg was mainly distributed in the strongly complexed phase. The low Hg content in FGD gypsum increases the ambiguity of assigning extraction fractions to certain Hg species by SCE. The fact that the primary compounds in FGD gypsum are HgS phases leads the leaching of Hg in the natural environment to be quite low, but a considerable amount of Hg may be released during the industrial heating process.
authors.affiliation: Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China. Electronic address: zhuzw11@mails.tsinghua.edu.cn.
authors.forename: Zhenwu
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China. Electronic address: zhuoyq@tsinghua.edu.cn.
authors.forename: Yuqun
authors.initials: Y
authors.lastname: Zhuo
authors.affiliation: Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China.
authors.forename: Yaming
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China.
authors.forename: Zhipeng
authors.initials: Z
authors.lastname: Wang
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002133:Calcium Sulfate / Q000737:chemistry*; D005591:Chemical Fractionation / Q000379:methods; D000066428:Coal Industry; D004784:Environmental Monitoring / Q000379:methods*; D008628:Mercury / Q000032:analysis*; D011210:Power Plants; D013696:Temperature
chemical_list: D000393:Air Pollutants; D008628:Mercury; D002133:Calcium Sulfate
keywords: FGD gypsum; Mercury speciation; Sequential Chemical Extraction; Thermal desorption