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Ignoring Emissions of Hg from Coal Ash and Desulfurized Gypsum Will Lead to Ineffective Mercury Control in Coal-Fired Power Plants in China Yufei Yang, Qifei Huang,* and Qi Wang State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China present in coal ash and desulfurized gypsum from the increased combustion of coal and the abundance of Hg removal facilities in Chinese coal-fired power plants. From China’s electrical industry statistics, coal ash and desulfurized gypsum yields from coal-fired power plants were approximately 480 million and 5.23 million tons, respectively, in 2010 and the recycling rates of coal ash and desulfurized gypsum were 68 and 67%, respectively. The remaining coal ash and desulfurized gypsum are typically randomly piled and mercury is continuously released to the environment. In China, coal ash is typically used as a mixing material for concrete, an alternative material for cement production and road building. Coal ash used as a mixing material is first mixed with cement to ercury is an important contaminant when emitted to the produce concrete and later hydrated. Although mercury in coal atmosphere because of its toxic effects on the environash is immobilized in cement, it can easily be released to the ment and human health, persistence in the environment, and environment (the diffusion coefficient of Hg is 1 × 10−14 m2/ global transport in air masses. Mercury has been classified as a s).4 Mercury is an element with a high volatility. Therefore, in global pollutant by United Nations Environment Programme the high temperature environment of a cement kiln, little (UNEP). Atmospheric mercury emissions in China rank mercury from coal ash that is used as an alternative material can number one in the world,1 with emissions from coal-fired enter the clinker (tests of more than 60 clinker samples in power plants the most substantial contributor. From the China indicated that the mercury concentration ranged from Chinese Ministry of Environmental Protection, coal consumption for thermal power generation in China was 160 000 0.01−0.02 mg/kg). Most of the mercury enters the smoke and t in 2010. The average Hg concentration in coal used for kiln ash. In Chinese cement companies, kiln ash is circulated combustion in China is approximately 0.19 mg/kg,2 so the total within the cement production system, so much of the mercury Hg emitted (including atmospheric Hg and solid Hg) from in the cement kiln system will be emitted in smoke. Mercury in coal-fired power plants was approximately 304 t in 2010. The coal ash used for road building can also be leached through Chinese Ministry of Environment Protection required the long-term washing by rain. Mercury release is also a problem in percentage of desulfurization equipment in coal-fired power desulfurized gypsum that is used to produce building materials plants to be up to 38.6% by the end of 2010. Mercury removal like gypsum. is achieved mainly through dust removal, desulfurization, and These problems highlight that if not enough emphasis is put denitrification facilities in China. Assuming that the percentages on mercury control in coal ash and desulfurized gypsum, of mercury removal for an electrostatic precipitator (ESP) and mercury emission control measures at coal-fired power plants an electrostatic precipitator coupled with wet flue gas will not be effective because the release of mercury is not being desulfurization (ESP+WFGD) are 38.6 and 46.9%, respeccontrolled. In the overall use of coal ash and desulfurized 3 tively, the overall solid Hg emissions from coal-fired power gypsum, all potential pathways for mercury release should be plants was approximately 138 t in 2010. avoided. For example, restricting the use of coal ash as an With the rapid economic development in China, coal alternative material for cement production would allow consumption in thermal power plants will continue to grow, pretreatment to be performed that could change the mercury reaching an estimated 1750 million tons in 2015. If the current species in coal ash and desulfurized gypsum, reducing the dust removal processes and efficiencies remain the same, solid mobility of mercury. Finally, a mercury concentration limit in Hg emissions in China will reach approximately 150 t in 2015. building materials should be incorporated to control mercury Emission standards for air pollutants from thermal power plants concentrations in buildings. implemented in 2012 in China included an emission limit (0.03 3 mg/m ) for Hg pollutants in air from thermal power plants, highlighting the increased emphasis on the removal of mercury Received: February 27, 2012 from atmospheric emissions of coal-fired power plants in Accepted: March 2, 2012 Published: March 9, 2012 China. It would be expected that more mercury would be
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© 2012 American Chemical Society
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dx.doi.org/10.1021/es300786d | Environ. Sci. Technol. 2012, 46, 3058−3059
Environmental Science & Technology
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AUTHOR INFORMATION
Corresponding Author
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[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (51178439) and national 863 project (SS2012AA063401).
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REFERENCES
(1) Arctic Monitoring and Programme (AMAP)/UNEP chemicals branch. Technical Background Report to the global Atmospheric Mercury Assessment.2008. (2) Wang, Q.; Shen, W.; Ma, Z. Estimation of mercury emission from coal combustion in China. Environ. Sci. Technol. 2000, 34, 2711−2713. (3) Srivastava, R. K.; Hutson, N.; Martin, B.; et al. Control of mercury emissions from coal-fired electric utility boilers. Environ. Sci. Technol. 2006, 40, 1385−1393. (4) Svensson, M.; Allard, B. Diffusion tests of mercury through concrete, bentonite-enhanced sand and sand. J. Hazard. Mater. 2007, 142, 463−467.
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dx.doi.org/10.1021/es300786d | Environ. Sci. Technol. 2012, 46, 3058−3059
