A Kinetic Surface Complexation Model of Adsorption-Desorption Processes.

Adsorption-desorption on the surface of solid minerals is one of the dominant reactions impacting the fate and transport of inorganic contaminants in soil environment. In recent few decades, numerous studies demonstrated that the sorption of many solutes on soils was time-dependent in various time scales. However, the commonly used surface complexation models did not address the kinetic behavior of sorption processes amid their equilibrium mass distribution formula. In this study, a general purpose kinetic surface complexation model is developed for simulating kinetic adsorption-desorption of metals and ligands on mineral surfaces under various chemical environment. The kinetic surface complexation model (KSCM) enables one to evaluate the impact of reaction variables such as temperature, pH, ionic strength, counter-ion, co-ion, as well as reaction kinetics on the dynamic distribution of solutes between dissolved and sorbed phases. The model assumes that the kinetic sorption is dominated by mass transfer through diffusion process. In addition to the equilibrium reaction constants, a first order mass transfer coefficient is proposed to capture the kinetics of cation- and ligand- exchange processes in soils. Results obtained with the numerical solution of the kinetic equations are assessed using observed kinetic sorption data published in literatures.