Kinetics of liquid phase batch adsorption experiments

Abstract

Batch adsorption experiments are carried out by adding a known amount of adsorbent to a liquid solution at a known initial concentration and following the evolution in time of the concentration of the adsorbate. This is a very common method to obtain equilibrium and kinetic information in liquid systems, but in most cases kinetic results are analysed on the basis of empirical models. Two phenomenological models based on macropore diffusion in beads and shrinking core kinetics are used to generate data that are then interpreted with the widely used unconstrained linear regression methods. The results show that for both cases R2 values close to unity are obtained leading to the incorrect interpretation of the mechanism of mass transport. It is recommended that batch adsorption experiments should be analysed using phenomenological models to obtain physical parameters that are applicable to other systems and to reduce the experiments required to characterise fully the kinetics of adsorption.