USE OF SURFACE COMPLEXATION MODELS IN SOIL CHEMICAL-SYSTEMS

This chapter presents five common surface complexation models of the mineral–solution interface and their use in describing soil chemical systems. Common model characteristics and adjustable parameters are discussed. For each model, surface species, chemical reactions, equilibrium constant expressions, and surface activity coefficients are described. Applications of the model to ion adsorption on soil minerals and soils are presented. Incorporation of surface complexation models into computer codes is also discussed. All surface complexation models are based on a balance of surface charge expression. They contain at least one coulombic correction factor to account for the effect of surface charge on surface complexation and explicitly define equilibrium constant expressions for surface complexes. They contain mass balance equations for each type of surface site and charge balance equations for each surface plane of adsorption. Thus, all models contain adjustable parameters—the equilibrium constants, the capacitance density for the ith surface plane, and the total number of reactive surface hydroxyl groups. © 1992, Academic Press Inc.