| In recent years, the toxic elements in coal have been research highlights in many countries, especially in China, the largest coal-consuming country in the world. The fluorine in coal is a toxic trace element. Its a gas product of fluorine: HF, had a pernicious influence on humans and animals. In this study, we take coals, slag, fly ash as targets to reveal the changes in the occurrence mode and migration of fluorine in a coal-fired power plant in Inner Mongolia, China.Fluorine content in coal was determined by high temperature combustion-fluoride ion selection electrode method.The precision and accuracy of this method were also analyzed.The results show that high temperature combustion fluoride ion selection electrode method has high precision and accuracy for determination of fluorine content. It was an effective method to measure fluoride content in coal and other complex minerals, and it was also simplicity of operator, practicability. The content of fluorine of coal is 169 PPM from a power plant in Inner Mongolia, and higher than that in the rest of the world(the average level in the world is 88 ppm). Fluorine is a volatile element in coal, low fluorine content in slag is 81 ppm. The fly ash particles have the stronger adsorption to the fluorine, and fluorine content in electrostatic precipitator(EPS) or a bag filter is higher than fluorine in coal. During coal combustion, the fluorine is immigrated into slag,fly ash and flue gas flow.Only 3.02% of fluorine remain slag(LZ), and a total of 23% immigrate into fly ash(QH)(8.05%), ash of EPS(HHC)(14.96%) and ash of a bag filter(HHX)(1.84%) during coal combustion. The rest of the fluorine are released into the flue gas flow, and only 1.24% are emitted into the environment, and 72.74% of the fluorine are absorbed by flue gas desulfurization gypsum. Fluorine in the coal-fired power plant discharges mostly as solid products; however, only tiny amounts of fluorine(1.24%) emitted into environment as gas products(HF, Si F4) cannot be captured.Extraction method is employed to reveal the changes in the occurrence mode of fluorine, and the content of fluorine is determined by fluoride ion selection electrode method. The leach liquor include water, alkali-solution, acid-solution and salt-solution.The results are as follows: the fluorine in YM mainly exists in insoluble inorganic mineral forms, such as Ca F2, Mg F2 and Al F3; the fluorine occurrence modes in LZ are inorganicvilliaumite, such as soluble Na F, KF, and insoluble Ca F2, which are difficult to break down even at high temperatures; and physically adsorbed fluorine and insoluble inorganic mineral fluoride(Ca F2, Mg F2 and Al F3) are the main occurrence modes of fluorine in HHC and HHX. The high fluorine content in fly ash is mainly attributed to physically adsorbed fluorine along the direction of the flue gas flow. The insoluble inorganic mineral fluoride content in fly ash is also high, but the gradually increasing fluorine content in fly ash is mainly caused by physical adsorption. Fluorine in the coal-fired power plant discharges mostly as solid products; however, very little fluorine as HF and Si F4 released into air cannot be captured.Mineral morphological of fluorine in coal, fly ash, slag were verified by environmental scanning electron microscopy(SEM) as comparing with results of extraction. Their result were consistent. The two methods can confirm mutually, and the conclusion is more reliablity and accuracy. |
