| Coal seam fires is widely distributed in the North of China.It possible has been a main source of the atmospheric mercury,and may lead to the serious mercury ecological risk in its surrounding.The study on coal fire mercury not only make environmental sense but also offer a new way to control the coal seam fire.In this paper,the Hg concentration,distribution,Hg emission flux,Hg isotopic characterization,Hg species,drilling hole data,etc in Wuda with typical coal fire was investigated,including coalfield,industrial park,urban,farm and wasteland.And then the mercury environmental geochemistry was investigated.The main results show as following:The Hg concentration in No.9 and No.10 coal seam from Wuda coalfield ranges from 0.168 to 0.243 ?g·g-1,with an average of 0.203 ?g·g-1.The minerals in the Wuda coal include clay minerals such as kaolinite,illite,and smectite,and non-clay minerals such as quartz,calcite,anatase,etc.The correlation coefficients between the Hg content and the LTA samples was up to 0.77,that show Hg occurrence is main inorganic.we conducted correlation between the mercury content and the percentages of minerals.The mercury in Wuda coal positively correlates pyrite(r=0.86)and total clays(r=0.63),that show mercury was associated with pyrite and clay.The average dustfall Hg concentration in coalfield,industrial park,urban,farm and wasteland was 289 ng·g-1,809 ng·g-1,160 ng·g-1,57 ng·g-1,48 ng·g-1,respectively.The average topsoil Hg was 216 ng g-1,242 ng·g-1,30 ng·g-1,30 ng g-1,respectively.Compared China tide and Wuda back ground values,the concentrations are significantly enriched in the coalfield,industrial,and urban areas.By analysis the geoaccumulation index,the results that the industrial park was the most serious dustfall Hg pollution,the moderate pollution and above account for 70%,the heavy pollution and extremely heavy pollution were up to 7%and 7%;the coalfield was the most serious topsoil Hg pollution,the moderate pollution and above account for 60%.The distribution of higher Hg concentrations is primarily observed downwind of the coal fire,suggesting that coal fires are the primary Hg source for Wuda.Some higher Hg values are also due to other factors,such as gangue hills and the topography of the coalfield,the use of activated carbon with HgC12 as a catalyst in the industrial park,and several coal washeries in the wasteland areas.The correlation coefficients between the Hg content of dustfall and topsoil in coalfield was lower than that of other areas,the reason of that was a part of topsoil Hg in coalfield directly coming from underground coal-fire.The Hg concentration of plants was significantly affected by coal-fire,and there was ecological risk of Hg.The Hg emission flux in the coalfield ranged from 14 to 318 ng·m-2h-1 with an average value of 90 ng·m-2h-1,and the average value for different areas varied,e.g.,coal-fire area 99 and 177 ng·m-2h-1;no coal-fire area 19 and 32 ng m-2h-1;and backfilling area 53 ng·m-2h-1.The Hg emission flux in the urban area ranged from 20 to 138 ng·m-2h-1 with an average value of 80 ng·m-2h-1.The Hg emission flux in the industrial park ranged from 2 to 199 ng·m-2h-1 with an average value of 71 ng·m-2h-1.By analysis of the correlation coefficients between the Hg emission flux and soil surface Hg concentration,minerals,and pH value,that suggested Hg continued to be emitted from an underground coal seam,even if there were no phenomena,such as vents,cracks,and smog from coal fire on the soil surface.This phenomenon occurred in all area types,i.e.,coal-fire area,no coal-fire area,and back filling area,which is universal in Wuda coalfield.Moreover,the effect of dust Hg was stronger than that of soil.By analysis the correlation coefficient between Hg concentration and CO,CO2,CH4 concentration in the drilling hole,the value of the correlation coefficients between Hg and CO,CH4 was higher,suggesting the Hg in drilling hole was main come from the coal seam.The mercury species in Wuda samples were investigated.Firstly,the affecting on mercury species from different atmospheres was investigated,such as argon,nitrogen,synthetic air(25%O2,75%N2)and oxygen,suggesting experiment effect was better under argon.The mercury species in No.9 and No.10 coal seam of Wuda coalfield was main HgS and HgSO4,and a small amount of HgC12 and HgO.HgC12 was main in dustfall,and it followed by HgO and HgSO4.The mercury species of topsoil was main HgSO4 with a small amount of HgC12 and HgO,and some samples have HgS.The samples showed a different MDF and MIF degree in Wuda.The ?202Hg value of coal ranged from-2.84‰ to-1.04‰,with an average of-1.97±1.78‰;the ?199Hg value of coal ranged from-0.06‰ to-0.04‰,with an average of-0.05±0.01‰.The 8202Hg value of dustfall ranged from-1.35‰ to-1.25‰,with an average of-1.30±0.08‰;the ?199Hg value of dustfall ranged from-0.14‰ to-0.12‰,with an average of-0.13±0.02‰.The ?202Hg value of topsoil ranged from-1.31‰ to-1.22‰,with an average of-1.26±0.08‰;the ?199Hg value of topsoil ranged from-0.12‰ to-0.10‰,with an average of-0.11±0.02‰.The 8202Hg value of CFS ranged from-1.66‰ to-1.34‰,with an average of-1.49±0.22‰;the ?199Hg value of CFS ranged from-0.04‰ to-0.05‰,with an average of-0.05±0.00‰.By comparing the isotopes ratios,the results show that the different value between the CFS and dustfall or topsoil,it mean that soil and CFS has different source of Hg or their Hg has undergone different transformation pathways;dustfall and topsoil has a source of Hg.The ?202Hg of CFS,dustfall and topsoil was more negative than that of No.9 coal seam.That was caused by not only the kinetic fractionation effect of burning and heating process but also the geologic chromatography effect of migration process in crack and hole.The 8202Hg of dustfall was more negative than that of topsoil,it was come from Hg2+ and MMHg photoreduction after atmospheric precipitation.On the whole,mercury environmental geochemistry in Wuda was investigated,by the Hg concentration,distribution,Hg emission flux,Hg isotopic characterization,Hg species,drilling hole data.The study make us get more deeply understanding on Hg environmental geochemistry in coalfield.In addition,the paper concluded that the mercury release channels from coalfire,the mechanism of soil surface Hg concentration abnormal,the samples Hg source in coal-fire area 9#. |
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