Studies of the Kinetics of Solute Adsorption at Solid/Solution Interfaces:  On the Possibility of Distinguishing between the Diffusional and the Surface Reaction Kinetic Models by Studying the Pseudo-First-order Kinetics

It is shown that the popular pseudo-first-order Lagergren equation can be applied to correlate kinetic adsorption data only in the adsorption systems that are not far from equilibrium. Also, it is shown that the Lagergren equation is then the limiting form of the kinetic equations developed by assuming both diffusional and surface reaction kinetic models. However, the theoretical interpretation of the coefficients in the Lagergren equation is then different for the two different kinetic models. The comparison of the theoretically predicted values of these coefficients with their experimentally determined values creates a chance to conclude whether the diffusional or the surface reaction model should be assumed to represent the kinetics of adsorption in an investigated adsorption system.