Surface Complexation Modeling of Fluoride Adsorption by Soil and the Role of Dissolved Aluminum on Adsorption

摘要

The adsorption processes of F- on a natural soil as a function of varying pH and F- concentration were evaluated by applying a surface complexation model (SCM) based on a single surface functional group with monodentate binding sites. A granitic soil from Tsukuba, Japan, was chosen as an example, and the SCM was developed to explain the pH dependency of F- sorption isotherms on the soil. Four possible surface complexation reactions were postulated with and without including dissolved Al. Optimized constants for F - surface complexation, and those for protonation and deprotonation, were used for the simulations. The SCM including dissolved Al and the adsorption of Al-F complex can simulate the experimental results, the decreasing trend of F- adsorption with the increase in pH, quite successfully. Also, including dissolved Al and the adsorption of Al-F complex to the model explained the change in solution pH after F- adsorption. Therefore, incorporation of dissolved Al and Al-F complex in model calculations of a soil-F system is an important improvement to predict F(- )concentrations of soil solutions.