Hydrochemical characteristics and cause analysis of high fluoride groundwater in Zhuanlongwan coal mine

In order to gain insight into the hydrochemical characteristics and formation mechanism of high fluoride groundwater in Zhuanlongwan Coal Mine, we conducted a comprehensive analysis of 48 samples including quaternary groundwater (QGW), sandstone groundwater (SGW), and mine water (MGW) using statistical analysis and hydrochemical methods. The findings demonstrate that the groundwater in Zhuanlongwan Coal Mine generally exhibits weak alkalinity, with predominant cations comprising of Ca2+ and Na+, and anions consisting of HCO3– and Cl–. The mean mass concentration of SO4 2–, Cl–, TDS, pH, and CO3 2– in groundwater follows the order of MGW>SGW>QGW, whereas HCO3– and F– exhibit the trend of SGW>MGW>QGW. Specifically, the average mass concentration of F– in QGW, SGW, and MGW is 0.76 mg/L, 4.55 mg/L, and 4.35 mg/L, respectively. Notably, most samples from SGW and MGW significantly exceed the permissible F−concentration threshold of 1.0 mg/L. The hydrochemical type of low fluoride (\begin{document}$\rho_{{\mathrm{F}}^{-}} $\end{document}1 mg/L) are mainly HCO3−Na (35.42%) and SO4·Cl−Na (45.83%). The dissolution of fluorinated minerals serves as the main source of F– in the high fluoride groundwater of Zhuanlongwan Coal Mine. Moreover, cation exchange, competitive adsorption, as well as the dissolution and precipitation of dolomite and calcite, are significant factors influencing the occurrence of high fluoride groundwater.