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

• Hydroxy-Al, Al13 pillaring cations were used to modify montmorillonite clay.
• The adsorption equilibrium of Al13 was achieved in 12 h as determined by kinetics.
• Adsorption of Al13 by montmorillonite followed the pseudo-second-order kinetic model.
• Al13 adsorption by Mt was found to be spontaneous and endothermic.

Hydroxy-Al pillaring agent was prepared and used to modify montmorillonite (Mt), and the effects of temperature, initial Al3 + 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 Al3 + 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 Al3 + 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.

Figure optionsDownload as PowerPoint slide