Hydrogeochemical characteristics of high fluoride bearing groundwater in the Hetao Plain, Northern China

This paper investigated the hydrogeochemical characteristics of high fluoride groundwater in Hangjinhouqi, the Hetao Plain, northern China, where more than 36,000 rural habitants have suffered from serious endemic fluorosis. In the study area, groundwater with high fluoride content (1.08-6.01 mg/L) are normally characterized as low calcium-contented, high bicarbonate contented and neutral to alkaline in pH, with an average calcium content of 34.21 mg/L, bicarbonate at 605.91 mg/L and pH value of 7.7. Geochemical modeling was performed to identify the relationship between F(-) and Ca(2+), HCO(3)(-) and pH value using PHREEQC. The modeling result show high pH value is in favor of the dissolution of fluoride bearing minerals; elevated calcium concentration may reduce the free F in the simulation solution by the formation of CaF(+); superfluous calcium causes reduction of total fluoride in the simulation solution as precipitation of fluorite; increased HCO(3)(-) may decrease the free Ca2+ concentration in the solution and accelerate the further dissolution of fluoride bearing minerals by the formation of CaHCO(3)(+).