Distribution of acidity of late Permian coal in border area of Yunnan, Guizhou and Sichuan

To investigate the distribution pattern of acidity in the Late Permian coals in the boundary area of Yunnan, Guizhou and Sichuan and its possible impact on Endemic fluorosis,about 83 samples of coal were collected from the endemic fluorosis area of Weixin and Zhenxiong in Yunnan,Hezhang and Dafang in Guizhou,Gulin and Xuyong in Si- chuan to determine the acidity,sulfate and fluorine content. The new discovery confirm that the pH of the Late Permian coals range from 1. 86 to 8. 62,with an average of 5. 70 (n = 83) and the proportions of acidic coal (pH≤5. 6) and normal coal (pH>5. 6) take account for 41% and 59% respectively,and 97. 1% of coal is outcrop coal. The pH of outcrop coals range from 1. 86 to 8. 62,with an average of 4. 86 (n = 55),and the pH of acidic outcrop coal reaches 3． 39(1． 82-5． 50,n = 33). The pH of coals in mine range from 4． 45 to 7． 94,with an average of 7. 36. The average pH of domestic coal ranges from 6. 71 to 7. 81,which shows that the acidity of outcrop is stronger than that of mine coal and domestic coal. The measured average value of total sulfate is 249 -64 706 μg / g with an average value of 7 070 μg / g (n = 83). The fluorine content in coal is 44-382 μg / g,with an average of 120 μg / g (n = 83),which is close to the background value of fluorine content in Chinese coal (130 μg / g). The pH and p( SO24- ) of coal is posi- tively correlated (correlation coefficient:0. 62),which could conclude that the form of acid may be acidic sulfate such as KHSO4 or NaHSO4 . When the clay with high fluorine content coexists with acidic coal in the study area,under cer- tain circumstances,such as heating or burning, they would lead to a chemical reaction producing volatile fluoride (HF). The acid and the high content of sulfate in coals may be derived from the oxidation of pyrite.