Selected Papers on Coal Petrology and Coal Geochemistry in Ren Deyi
Coal is a complex geological body formed in various geological historical periods, and it is an essential energy and chemical raw material for people to survive. Coal contains a variety of potentially toxic trace elements, which will cause serious pollution to the environment during coal processing and utilization [1 ~ 8]. Coal burning is the main pollution source of mercury in the atmosphere, and more than 90% of mercury in coal enters the atmosphere during combustion [1, 6]. The amount of mercury released during the combustion of coal and oil in the world exceeds 1600 tons per year on average [7]. Mercury vapor is toxic, and elemental mercury can be transformed into methyl mercury with greater toxicity under the action of anaerobic methanogenic bacteria [6,8]. Therefore, it is of great significance to study the distribution and occurrence of mercury in coal for understanding the washability of mercury in coal and reducing the pollution of mercury in coal to the environment.
Stock and Cucuel( 1934) discovered mercury in coal for the first time. Dvornikov( 198 1) proposed that mercury in coal exists in three forms: cinnabar (HgS), metallic mercury and organic mercury compounds. Swaine [9] thinks that mercury in coal is mainly distributed in pyrite and sphalerite. Finkelman [10] found micron-sized mercury sulfide in coal. Most of the late Permian coals in southwest Guizhou are high-sulfur coals [1 1], and some coals have high mercury content. In this paper, the mercury in the main minerals of the late Permian coal seam in southwest Guizhou was studied preliminarily.
I. Samples and analytical methods
1. Geological survey and samples of the sampling area
The sampling area is located in the "Qianxi fault depression area" between Shuicheng-Ziyun fault, Nanpanjiang fault and Panxian fault, and the middle part is cut by Shizong-Guiyang fault, which is a tectonic active area [1 1, 12]. The metamorphic degree of the upper Permian Longtan Formation coal in this area is high [1 1]. The sulfur content in coal is mostly high. Samples were collected from Dachang in Qinglong County, Sang Mu in Zhenfeng County and Dayakou in Xingren County. Macro minerals in coal seams are divided into the following seven types (Table 1):
Table 1 Mercury Content Table of Main Associated Minerals in Southwest Guizhou Coal Seam
① Pyrite vein (QL07) formed by late leaching; ② massive pyrite (qg061); ③ Pyrite veins (XD 011) formed by late low-temperature hydrothermal solution; ④ Pyrite nodule (Zm022); ⑤ Clay mineral (zm03); ⑥ calcite vein (zm051) formed by late low-temperature hydrothermal solution; ⑦ Black migmatite veins formed by late low-temperature hydrothermal solution (XD 10).
Although there are many timely detritus in coal in southwest Guizhou, the mercury content in the timely detritus is very low [9], so the timeliness of detritus is not analyzed. Pyrite veins and calcite veins formed by low-temperature hydrothermal solution are easily distinguished from pyrite veins and calcite veins formed by leaching in coal seam profile. The former is bundle-shaped, irregular and has obvious extrusion marks. While the latter has fewer bifurcations and a regular shape.
Microscopic identification shows that QG06 1 samples are all composed of pyrite. QL07 and XD0 1 1 samples contain a small amount of other minerals; Pyrite in ZM022 sample has metasomatism trace; ZM03 contains timely detritus and a little pyrite; ZM05 1 sample is mainly composed of calcite; XD 10 sample is composed of calcite, pyrite and coal detritus particles, with a small amount of time and a thickness of about 5mm, which is of low-temperature hydrothermal origin and is rare in coal.
2. Analytical methods
The separated samples were crushed and ground to less than 200 meshes, and a certain amount of reduced samples were taken for digestion, and the mercury content in the samples was analyzed by cold atomic absorption spectrometry. The instrument used is F732-S mercury meter. Part of the reduced sample is decomposed into
Second, the analysis results and discussion
1. Mercury content in different minerals
The content of mercury in the samples analyzed by cold atomic absorption spectrometry is listed in table 1. The analysis results show that the average mercury content of 14 coal samples in this area is 0.172×10-6; The mercury content of clay minerals in coal is 0. 174× 10-6, which are basically the same. The mercury content in other minerals is 10 ~ 120 times higher than that in coal, indicating that mercury in coal in southwest Guizhou is mainly distributed in associated minerals.
The mercury content in pyrite of different genesis is quite different [13], and the mercury content in pyrite of late low-temperature hydrothermal origin is (22.5× 10-6)? (3.5 1× 10-6) in globular pyrite > (2.97× 10-6) in massive pyrite >: (1.80× 10-6) is caused by late leaching. The mercury content in late low-temperature hydrothermal pyrite is 12 times higher than that in late leaching pyrite. The mercury content in pyrite vein (22.5× 10-6) and calcite vein (1 1.9× 10-6) in the middle and late stage of coal in southwest Guizhou is the highest, and the high mercury content in calcite in coal seam has not been reported before. There are obvious metasomatism traces in pyrite nodules, indicating that mercury must be added in the later stage.
The mercury content in black migmatite veins formed by low-temperature hydrothermal solution is obviously lower than that in pyrite veins and calcite veins formed by low-temperature hydrothermal solution. Firstly, because the black migmatite vein contains a lot of coal dust (about 23.5%), the mercury content in the organic components of coal is very low; Second, it may be due to the differentiation of low-temperature hydrothermal solution, which leads to the obviously low mercury content.
2. The existing forms of mercury in associated minerals in coal.
The main associated minerals in coal were observed under high power optical microscope and scanning electron microscope, and no independent mercury-containing minerals were found. Therefore, it is speculated that mercury in the main associated minerals in coal may exist in two forms: ① nanoscale mercury minerals. The properties of nano-materials are far from ordinary particles, and nano-materials have strong diffusion ability and strong solid-state migration ability [14]. Nano-mercury minerals are distributed in various main associated minerals in coal. ② It exists in isomorphic form. Mercury is a sulfur-loving element and can exist in pyrite in the form of isomorphism [15].
3. The main source of mercury in coal
The average content of mercury in the crust is 77× 10-9 [16]. The distribution area of ancient continental basalt in Sichuan and Yunnan is the main continental source area of late Permian coal-bearing rock series in the study area. The average mercury content of basalt samples near Qinglong is 4.19×10-6 [17]. Because the ionization potential of mercury is very high, the ionization potential of one electron of mercury is 10.39eV, and the ionization potential of two electrons is 29.06eV. The high ionization potential determines that mercury is easy to become an atom [6]. It is precisely because of the difficult ionization and easy dispersion of mercury that the mercury content in terrestrial debris and plants transported to peat bogs is very low, so the mercury content in primary coal mines is low. However, in the high mercury background area, acidic surface water and groundwater may contain high mercury content [7], which leads to high mercury content in veins leached and deposited in some coals.
The main source of mercury in coal in southwest Guizhou is low-temperature hydrothermal solution. The temperature measurement of inclusions shows that the formation temperature of dikes in this area is 130 ~ 300℃, and most of them are 160 ~ 200℃. Low-temperature hydrothermal deposits such as antimony, arsenic and mercury are widely distributed in this area [17, 18], which also shows that the low-temperature hydrothermal activity in this area is very strong. The mercury content of low-temperature hydrothermal veins in coal is obviously higher than that in coal. The mercury content in low-temperature hydrothermal calcite is more than 65 times that in coal, and that in low-temperature hydrothermal pyrite is about 120 times that in coal. Therefore, the low-temperature hydrothermal solution in southwest Guizhou is the main source of mercury in some coals.
In a word, the mercury content in the coal seam in southwest Guizhou is low, and the groundwater leaching increased the mercury content in the coal seam in the later stage, and a large amount of mercury was added to the coal seam in the later stage due to the low-temperature hydrothermal activity.
4. Occurrence state of mercury in coal
Through the analysis of mercury in the main associated minerals [19,20] in coal and coal seam, combined with optical microscope, scanning electron microscope and energy spectrum analysis, it is preliminarily determined that the mercury content in the organic components of coal in southwest Guizhou is very low, and mercury is mainly distributed in minerals. There are great differences in mercury content in different kinds of minerals and different producing areas. There is basically no mercury in time [9], and the content of mercury in clay minerals is low, and mercury is mainly distributed in pyrite and calcite. There are also obvious differences in mercury content in pyrite from different origins. This shows that mercury in coal is mainly inorganic.
Mercury in coal in Southwest Guizhou mainly exists in mineral form, which can reduce the ash content in coal washing process and greatly reduce the mercury emission during coal burning.
This paper is directed by C.L.Chou, a researcher of Illinois Geological Survey, and Professor Jin of China University of Mining and Technology. Guizhou Coalfield Geology Bureau, Zhenfeng County Government and Qinglong County Coal Management Bureau gave great support and help to the field work. Thank you here.
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[1] Wang Qichao, Ma Rulong. Mercury in coal and its ash. China environmental science, 1997, 17 (1): 76 ~ 78.
[2] Rasmussen P.T. Existing Methods for Estimating Atmospheric Mercury Flux in Remote Areas. environment Sci。 Technology. , 1994,28( 13) : 2233 ~ 224 1
[3] Sorensen J.A. Glass G.E. Schmidt K.W. Regional model of wet mercury deposition. environment Sci。 Technology. , 1994,28( 12) : 2025 ~ 2033
[4] Germani M.S., Zole W.H. Gas phase concentrations of arsenic, selenium, bromine, iodine and mercury in the chimney of coal-fired power plant. environment Sci。 Technology. , 1988,22( 9) : 1079 ~ 1085
[5] Swaine D J, Goodarzi F. Environmental aspects of trace elements in coal. Klfuwer Academic Press, 1995
6 United Nations Environment Programme, World Health Organization. Environmental health benchmark (1): mercury. Beijing: China Environmental Science Press, 1990.
Chen Jingsheng, Deng Jiashan, Peng Tao, etc. Environmental geochemistry. Beijing: Ocean Press, 1990.
Liao. Pollution harm and migration of trace heavy metals in the environment. Beijing: Science Press, 1989.
[9] Swaine D.J. Trace elements in coal. Butterworth, London, 1992
[10] Finkelman R.B. uses occurrence mode information to predict the removal of harmful air pollutants before combustion. J. Coal area al, 1993,12 (4):132 ~134
Editor Wang Xiaochuan. Sedimentary environment and coal accumulation law of late Permian coal-bearing strata in western Guizhou, southern Sichuan and eastern Yunnan. Chongqing University Press, 1996.
Liu Wenjun, Zeng Yunfu, Zhang Jinquan, et al. Geochemical characteristics and tectonic environment of volcanic rocks in Youjiang basin. Geology of Guangxi,1993,6 (2):1~14.
[13] Barton E.S., Hall Bauer D. K. Trace elements and U-Pb isotopic composition of pyrite types in Proterozoic black reefs in Transvaal sequence, South Africa: implications of genesis and age. Chemical geology, 1996,133:173 ~199.
Liu, ren tianxiang, Application of underground nanomaterials in mineral deposit exploration. Bulletin of Mineral Rock Geochemistry, 1997, 16 (4): 250 ~ 253.
Zhao, Zhang Benren. Geochemistry. Beijing: Geological Publishing House, 199 1.
Mars. Analytical chemistry of minerals. Beijing: Science Press, 1994.
[17] Guizhou Provincial Bureau of Geology and Mineral Resources. Regional geology of guizhou province. Beijing: Geological Publishing House, 1987.
[18] China Deposit Editorial Committee. Deposits in China (1). Beijing: Geological Publishing House, 1989.
Zhou Yiping. Source and occurrence of mercury in coal in Laochang mining area. Coalfield Geology and Exploration,1994,22 (3):17 ~ 21.
[20] selected elements in main minerals of bituminous coal as determined by Palmer C.A. and Lyons P.C.: the meaning of removing environmentally sensitive elements from coal. J. Coal Geology,1996,32:151~166.
Distribution of Mercury in Main Associated Minerals of Coal Seam in Southwest Guizhou
, Ren Deyi, Xu Dewei, Liu,,
(Beijing Graduate School of China University of Mining and Technology, Beijing, 100083)
(Institute of Environmental Health, Chinese Academy of Preventive Medicine, Beijing, 10002 1)
(Shanxi Coal Geology Company Taiyuan, 030045)
Abstract: Seven kinds of main minerals with different genesis in southwestern Guizhou coal were identified by microscopic analysis, scanning electron microscope-energy spectrum analysis, inclusion analysis and sulfur isotope analysis. Determination of mercury in coal and minerals by cold atomic absorption spectrometry. The results show that mercury in coal in southwest Guizhou is mainly combined with minerals. The mercury content in pyrite of different genesis is obviously different: epithermal pyrite vein (22. 5 × 10- 6) ? Spherical pyrite (3. 5 1 × 10- 6) > massive pyrite (2. 97 × 10- 6) > leaching pyrite from vein (1. 80 × 10- 6). In addition, the mercury content in epithermal calcite veins is also very high (1 1. 9 × 10- 6). Mercury in coal in southwest Guizhou mainly comes from epithermal. Clean coal technology can remove most mercury from coal.
Keywords: coal seam; Late Permian; Mercury; Happen; Minerals in coal; Southwest Guizhou
(This paper was co-authored by,, Xu Dewei, Liu, and was originally published in Geological Review, Vol.45, No.5).