Geochemical Characterization of Fluoride in the Groundwater of the Huaibei Plain, China

Forty-two groundwater samples were collected for the geochemical characterization of fluoride in the Huaibei Plain, a high fluorine area, in Northern China. The concentration of fluoride in the groundwater was from 0.20 to 3.75 mg/L, and 23.81% (n = 9) of the samples exceeded the drinking water standard of 1.5 mg/L recommended by the World Health Organization. The groundwater was alkaline (pH 7.14-8.67), brackish (total dissolved solids 421-1196 mg/L), and the water was classified as sodium bicarbonate, calcium bicarbonate, calciumsodium bicarbonate, and chloride-sodium bicarbonate. This prevailing characteristic may be attributed to mineral weathering, water-rock interactions, and ion exchange in the aquifer. The main source of fluorine in the groundwater may be from the leaching of minerals. The elevated concentration of fluoride in groundwater may be derived from the calcite-fluorite minerals. This study also discusses several factors affecting the fluoride concentrations in groundwater. High fluoride concentrations are associated with weakly alkaline conditions, moderate total dissolved solids, and calcium and sodium ions as the dominant ions. Correlations between fluoride and sample depth and SO42+ were not observed. All samples were below the solubility product curve of CaF2, which may be explained by positive correlation between fluoride and total dissolved solids. Evapotranspiration and runoff conditions also favor fluoride enrichment in groundwater.