Mobility and contamination assessment of mercury in coal fly ash, atmospheric deposition, and soil collected from Tianjin, China

Abstract

Samples of class F coal fly ash (levels I, II, and III), slag, coal, atmospheric deposition, and soils collected from Tianjin, China, were analyzed using U.S. Environmental Protection Agency (U.S. EPA) Method 3052 and a sequential extraction procedure, to investigate the pollution status and mobility of Hg. The results showed that total mercury (HgT) concentrations were higher in level I fly ash (0.304 µg/g) than in level II and level III fly ash and slag (0.142, 0.147, and 0.052 µg/g, respectively). Total Hg in the atmospheric deposition was higher during the heating season (0.264 µg/g) than the nonheating season (0.135 µg/g). Total Hg contents were higher in suburban area soils than in rural and agricultural areas. High HgT concentrations in suburban area soils may be a result of the deposition of Hg associated with particles emitted from coal-fired power plants. Mercury in fly ash primarily existed as elemental Hg, which accounted for 90.1, 85.3, and 90.6% of HgT in levels I, II, and III fly ash, respectively. Mercury in the deposition existed primarily as sulfide Hg, which accounted for 73.8% (heating season) and 74.1% (nonheating season) of HgT. However, Hg in soils existed primarily as sulfide Hg, organo-chelated Hg and elemental Hg, which accounted for 37.8 to 50.0%, 31.7 to 41.8%, and 13.0 to 23.9% of HgT, respectively. The percentage of elemental Hg in HgT occurred in the order fly ash > atmospheric deposition > soils, whereas organo-chelated Hg and sulfide Hg occurred in the opposite order. The present approach can provide a window for understanding and tracing the source of Hg in the environment in Tianjin and the risk associated with Hg bioaccessibility.

Acid leaching of CaOSiO2 resources

“…The latter, multistep process, wherein calcium ions are first leached from the mineral matrix by acetic acid and, then, precipitated as carbonate in a separate step [10][11][12][13]. The indirect carbonation is considered more attractive one, while there have been some important research on the contamination by minor components such as As [14] and Hg [15]. The method not only accelerates the carbonation rate, but also produces pure calcium carbonate as well as byproduct of silica, if selectively leached [11].…”

Trace metals, organic carbon and nutrients in the Beidagang Wetland Nature Reserve, northern China

“…The Beijing-Tianjin-Hebei region has a very large consumption of energy and power, the majority of which is sourced from coal combustion, identified as the major source of particulate Hg in Beijing and Tianjin [ 5 , 6 ].Total global Hg emissions from anthropogenic sources to the atmosphere range from 1900 to 2900 t/yr; East Asia currently accounts for almost 40% of total global anthropogenic emissions of Hg [ 43 ].Total anthropogenic Hg emissions in China were estimated to have continuously increased from 356 t in 2000 to 538 t in 2010 with an average annual increase rate of 4.2% [ 44 ]. Coal-fired power plants in China emit less than 100 tons Hg directly to the atmosphere every year due to nationwide air control actions [ 45 ].…”

“…Wet deposition of Hg in Beijing was 101.52 μg/(m 2 yr) (Nov 1994–Nov 1995) and 123.09 μg/(m 2 yr) (Nov 1995–Nov 1996) [ 50 ]. The atmospheric dry deposition fluxes of Hg and Cd in Tianjin were 35.3–37.5 μg/(m 2 yr) and 97.4–103.6μg/(m 2 yr), respectively [ 5 ]. Atmospheric deposition of Hg in the Bohai Sea was 31.0 μg/(m 2 yr) [ 51 ].…”

Blast-furnace process as a source of anthropogenic mercury emissions

“…Mercury content in blast furnace slag released in liquid form from the surface of the pig iron is about 50.0 μg Hg/kg [21,22].…”