Adsorption/desorption of a dye by a chitosan derivative: Experiments and phenomenological modeling

• Adsorption and desorption experiments for reactive dye on a chitosan derivative.
• A phenomenological (mechanistic) model for adsorption and desorption is developed.
• Simulation of repeated cycles with adsorption/desorption steps is performed.
• Adsorption efficiency reduction is due to mass conservation requirement.

The literature for adsorption of solutes from the liquid phase to solids or gel adsorbents under batch conditions is vast. The corresponding literature on the fundamentals of the process and its modeling from empirical to physical (phenomenological) models is also very extensive. This is not true for the process of desorption, despite its importance for the adsorption process to acquire economical viability. The literature for batch desorption is very small compared to that of adsorption and the corresponding theoretical/modeling studies are almost absent. In order to study the dynamics of batch adsorption/desorption process, a novel adsorbent–adsorbate combination of a chitosan-based derivative and a reactive dye is considered. Adsorption and desorption equilibrium experiments at optimal pH values were performed for three temperatures. Kinetic experiments were performed at three temperatures and three values of initial dye concentration in the solution (for adsorption) and in the adsorbent particle (for desorption). Typical analysis for equilibrium and kinetic data is presented. In addition, a phenomenological kinetic model is developed and fitted to the data assuming complete reversibility of the adsorption/desorption process. The model is extended to simulate batch adsorption/desorption cycles, which are typically studied experimentally in the literature. It is shown that the reduction of the adsorption efficiency during the cycles is not necessarily due to thermodynamic irreversibility of the process but may be due to the total solute mass conservation requirement.