Effects of Sediment Lithology and Groundwater Hydrochemical Characteristics on Fluorine Transport at Water-Soil Interface

Fluorine transport at water-soil interface affects formation of high fluoride groundwater.High fluoride groundwater occurring in Datong Basin is a serious problem,which is typical in China.In this paper,efforts were made to analyse the distributional characteristics of fluorine content and fluorine forms in the sediments of different lithologies,and to investigate the influence of pH,Ca₂₊,HCO^-₃ and H₂PO^-₄ on fluorine transport at water-soil interface using static experiments.The results show that contents of different fluorine forms in sediments descended in the following sequence:residual F ≥Fe/Mn oxide-F>water soluble F>organic F>exchangeable F.The order of fluorine contents in the aforementioned forms in different lithologies is:clay>silty clay>silt,in which clay minerals and calcite are main fixed fluorine minerals in sediments.In addition,the solution pH value and the concentrations of Ca²⁺,HCO^-₃ and H₂PO^-₄ are closely related to adsorption-desorption and dissolution-precipitation equilibrium of fluorine on the surface of sediments.The adsorption capacity of sediments on fluorine decreases with increasing pH and HCO-3concentration,but increases with the concentration of Ca²⁺ and H₂PO^-₄.