Geochemical characteristics of fluorine in coal within Xiangning mining area, China, and associated mitigation countermeasures

The geochemical characteristics of fluorine in coal obtained from 534 borehole exploration data and mining test data from the Xiangning mining area were studied, and fluorine emissions were calculated. Results reveal that the fluorine content in Carboniferous-Permian coal in the mining area ranges from 2.00 to 911.00 mg/kg, and the Carboniferous coal seam contents are generally higher than those of the Permian system. The calculated average fluorine contents in Nos. 5 and 12 coal seams of the Carboniferous system are 203.42 and 308.00 mg/kg, respectively, and therefore, both are high-fluorine coal. In addition, the calculated mean fluorine contents of Nos. 2 and 10 coal seams are 168.58 and 187.02 mg/kg, respectively, which are higher than average value of Chinese and global coal values. The highest fluorine content of 896.00 mg/kg is found in medium- to high-fluorine coal. Fluorine in coal mainly exists in an inorganic bound state in forms such as fluorapatite and calcium fluoride. The Xiangning Coal Mine predominantly produces coal for coking and power, and the release of fluorine during coal combustion is harmful to the environment. According to the information obtained in relation to coal resource reserves and development planning, the amount of fluorine released from combustion is estimated at 2258.1 t/year and is estimated to reach 4862.9 t/year by 2020. Coal washing is an effective way of reducing fluorine emissions, and flotation experiments have shown that this can reduce the amount of fluorine by up to 30–47%. Different engineering measures, such as denitrification and desulfurization, can also significantly reduce the amount of fluorine released during coal combustion and can thus be employed to reduce the associated environmental impacts.