Statistical physics modeling of equilibrium adsorption of cadmium ions onto activated carbon, chitosan and chitosan/activated carbon composite

The adsorption ability of activated carbon, chitosan, and chitosan/activated carbon composite for cadmium separation from aqueous solution was analyzed via statistical physical modeling. The equilibrium data were analyzed by the Langmuir, Hill, double layer model, and multi-layer model with saturation isotherm models. The results showed that the multi-layer model with saturation could well describe the data. The number of adsorbate ions per site, the receiver site density, the number of formed layers, and the energies of adsorption relative to the different layers were estimated by numerical simulation. The results showed that the chitosan/activated carbon had a higher receiver site density and a higher amount of adsorbed ions than the other two adsorbents. The results showed that the cadmium adsorption onto the activated carbon/chitosan composite was a monolayer and exothermic process. With increasing temperature, the amount of cadmium adsorption decreased due to the fact that the number of receiver adsorption sites decreased. Also, the statistical physics modeling indicated that the geometry of the cadmium ions adsorbed onto the adsorbent surface was parallel.