Utilization of desulfurization gypsum potentially impairs the efforts for reducing Hg emissions from coal-fired power plants in China

Abstract

The thermal instability of most mercury (Hg) species in flue gas desulfurization (FGD) gypsum may lead to the release of large amounts of Hg into the atmosphere. In this study, gypsum samples were collected from 13 major coal-fired power plants (CFPPs) for evaluating the Hg thermal stability within a temperature range of 100 - 200 °C. Results indicated that the release ratio of Hg from FGD gypsum varied considerably among the CFPPs. Such significant differences were caused by different proportions of the major Hg compounds, especially of HgClx (HgCl₂ and Hg₂Cl₂), in the FGD gypsum samples. The release ratio appeared extremely sensitive to changes in the treatment temperature and duration. Wallboard manufacturing and its use as cement retarder are the leading causes of Hg emission (corresponding to > 95% of the total) during FGD gypsum resource utilization. The total average Hg emitted due to FGD gypsum resource utilization in China in 2017 was estimated to be 11.42 tons (ranging between 2.15 - 38.35 tons), which accounted for about 23.8 % (ranging between 4.6 - 79.8%) of the stack Hg emissions from CFPPs in that year. The results of this study indicate that the resource utilization processes of FGD gypsum are important Hg emission sources and that they should be considered with care in future emission control policies.