Geochemistry of Fluorine in Shallow Ground Water

Abstract

The Xingtai piedmont plain in Hebei Province is a representative area in northern China where endemic fluorosis is serious and shallow high-F groundwater is distributed. The fluoride concentration of the shallow high-F groundwater is usually in the range of 1.0 — 2.0mg/l in this area. The F-bearing minerals for biotite and hornblende and the adsorbed and dispersed fluorides are distributed in the Quaternary deposits, particularly the Holocene deposits are the main supply source of fluorine for the shallow groundwater. In the distribution area of the shallow high-F groundwater, the unsaturated soils and groundwater constitute an interactive hydrogeochemical system. The unsaturated soils have an important effect on fluoride migration and accumulation. According to the experimental analysis and the coupled model for fluoride hydrodynamic transport-chemical reaction, the increase of F concentration of the shallow high-F groundwater can be effictively controlled by regulating the burial depth of the shallow groundwater to be greater than 4.0–6.0m. In the shallow ground water F−, MgF+ and CaF+ are the major fluorine species, and the ratioes of aMgF +, and aCaF + to the molalities of total fluoride are 79.35–96.51%, 3.09–19.17% and 0.32–3.01%, respectively. These F species have different influences on endemic fluorosis, of which MgF+ may have more important effect on endemic fluorosis in the area. The mass-balance model of fluoride suggests that average fluoride contents of 1.55mg/l in the shallow high-fluoride ground water are mainly originated from the dissolution of 0.0393mmol/KgH2O fluorine-bearing biotite along flow path from the mountain to the plain.