| 其他摘要 | With a concentration scope of 20-500 mg/kg and an average value at 150 mg/kg, fluorine is one of the abundant trace elements in coal. Because of its presence in the daily diet at varying levels, fluorine often has an extraordinary significance in health and environments. During the combustion of coal, fluorine is released into the.fume in the form of HF, most of which enters the o atmosphere. Statistical data collected by the Chinese Ministry of Health in 2001 from 201 counties of 14 provinces, autonomous regions, and municipalities in China indicates that coai-burning fluorosis led to 18,138,780 cases of dental fluorosis and 1,594,799 cases of skeletal fluorosis. Coal-burning fluorosis in China is therefore one of the most serious health problems resulting from environmental pollution anywhere in the world. Based on the progress of study on fluorine in coals, this dissertation mainly studies the fluorine content and its distribution in Chinese coals, the environmental geochemistry of coal-burning endemic fluorosis, the fluorine reduction by coal cleaning and the determination of fluoride in corn and chili. Based on the study, some conclusions can be drawn: 1. Fluorine contents in Chinese coals are achieved through a designed nationwide samples collecting and consistently determining by the most effective method i.e. pyrohydrolysis. The contents of fluorine in Chinese coals show logarithm normal frequency distributions. The estimate of the most probable fluorine concentration for Chinese coals can be designated as 136 ppmw with the range for most of the Chinese coals of 47-347 ppmw. 2. The concentration of fluorine versus ash content in 288 coal samples was studied. A significant positive correlation is inferred from this data, showing that fluorine increases in the samples studied, as does the ash content, suggesting that the fluorine compounds present in the Chinese coals are mainly of an inorganic nature. 3. Fluorine in coal is predominantly associated with the inorganic constituents, and it is not affected when coal developed from lignite coal to anthracite. The fluorine content varying from lignite coal to anthracite can't be attributed to the coal-rank's varying. 4. Fluorine contents in coal increase from C_1, J_2, J_1, P_1 C_3, C_2, P_2. J_3, R to T_3. The concentration of fluorine in coal is strongly influenced by geological factors such as sedimentary environment, character of source rock, tectonic setting, and hydrogeological conditions. Most of these parameters have regional characteristics, whereas China's abundant coal resources are spread over widely distributed coal fields with large variations in coal-forming periods. Therefore, it is difficult to get any consistent relationship between the fluorine content and the coal-forming period for the nation as a whole. 5. The clay mixed with the coal to make coal-clay is derived from illuvial lower soil and has a high fluorine level. The fluorine content of most coals in China is relatively low. Because of the similar geochemistry and the essentially identical habits of coal-clay usage in coal-burning endemic fluorosis areas, clay remains a major source of endemic fluorosis in China. 6. Little fluorine pollution of surface water and plant is deduced from the stone-like coal's- weathering and leaching. Fluorine released- from stone-like coal combustion results in serious fluorosis. To improve stove and abandon the traditional backward habit of food baking and improve the room sanitation to avoid the cpntamination of dust is effective in get rid of fluorosis. 7. Physical coal cleaning techniques are effective in fluorine reduction. At the same time, coal cleaning offers numerous benefits. It reduses the ash-forming mineral content of coal and increases the heating value, reducing transportation costs and increasing boiler efficiency. Coal cleaning also provides environmental benefits by reducing the sulfur dioxide and other HAPs emissions potential of the coal and the amount of ash for collection and disposal. 8. Fluorine in corn can be totally extracted by acid lixivium by once. Due to its abundant lipid, fluorine in chili can be totally extracted by several times. The fluorine content in the residue of acid lixivium is a constant. These factors should be taken into account when the limits is laid down for fluoride exposure and fluorine levels in foodstuff. |
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