Kinetics and thermodynamic analysis of the adsorption of hydroxy-Al cations by montmorillonite

Hydroxy-Al pillaring agent was prepared and used to modify montmorillonite (Mt), and the effects of temperature, initial Al^3 + concentration and contact time were investigated by using a batch technique. The results showed that the uptake of Al₁₃ by Mt increased with increasing temperature, initial Al^3 + concentration and contact time. The adsorption equilibrium was achieved in 12 h as determined by kinetics. The adsorption kinetics demonstrated that the adsorption of Al₁₃ by Mt followed the pseudo-second-order kinetic model. The adsorption isotherms at the temperatures of 40, 60, 80 and 90 °C were determined and simulated using Langmuir, Freundlich and Redlich-Peterson models. The three kinds of isotherms could represent the experimental data well. The specific surface areas and pillar density increased while the total porous volumes slightly decreased with increasing Al^3 + concentrations. The XRD result showed that adsorbed Al₁₃ ions were located in the Mt interlayer spaces through monolayer adsorption. Thermodynamic analysis of adsorption process showed that the adsorption of Al₁₃ by Mt was spontaneous, endothermic with increasing disorder during the adsorption process and mainly physical in nature.