Weathering of Clay-Pyrite of Coal-Bearing Formation in the Endemic Fluorosis Area of Southwest China

Abstract

It is common practice to use clay for coal-burning in fluorosis areas on the border of Yunnan, Guizhou, where coal-bearing strata is widely outcropped, and clay for coal-burning is usually considered to be collected from efflorescent clay in coal-bearing strata by some scholars. However, the relevant chemical properties of the clay, the mechanism that causes the fluorosis are not clear and the chemical forms of fluorine species present during transfer from the clay to the human body remain unclear. In this study, approximately 71 samples of efflorescent clay of coal-bearing strata were collected from seven counties in this area, and the results showed that those samples had a high-fluorine content with an average of 751 μg•g -1 (237-1,764 μg•g −1 , n = 71). The clays were rich in acid with an average pH of 5.81 (2.39-8.25, n = 71) and the acidic clays accounted for 52% of the total clay samples. The sulfate (SO 4

Fluorine pollution in a sheep fluorosis area of the northern Helan Mountains, Ningxia, China

“…It has been shown that the weathering of clay-pyrite in coal produces HSO 4 − and sulfate, which further promote the release of fluoride from the clay. 35 These may be the root cause of the high concentration of fluoride, sulfate and acid in the surface soil of the northern Helan Mountains, resulting in fluorosis in sheep in this area.…”

“…− and sulfate, which further promote the release of uoride from the clay. 35 These may be the root cause of the high concentration of uoride, sulfate and acid in the surface soil of ) in acidic topsoil.…”