Removal of aniline from aqueous solution by activated kaolinite: Kinetic, equilibrium and thermodynamic studies

Abstract

In this study, the adsorption kinetics, equilibrium and thermodynamics of aniline on native (NK) and acid activated (AK) kaolinites were examined. It was shown that modification of kaolinite with acid not only increases the adsorption capacity of the adsorbent from 109.89 to 256.41 mgg−1for aniline but also its initial sorption rate for aniline, suggesting the activated kaolinite with higher adsorption capacity have great potential application in removal of aniline from water and wastewater. Adsorption efficiency for AK reached at about 91% while it was at about 75% for NK. The kinetics of adsorption of aniline was discussed using three kinetic models, the pseudo-first-order, the pseudo-second-order and the intra-particle diffusion model. The experimental data fitted very well the pseudo-second-order kinetic model due to the higher correlation coefficient and lower sum of squared errors (SSE,%) values, and a good agreement between the experimental and the calculated qe values. Experimental results were also analysed by the Langmuir, Freundlich and Dubinin–Redushkevich (D–R) isotherm models. RL separation factor for Langmuir and the n value for Freundlich isotherm show that aniline are favourably adsorbed by NK and AK. The negative value of ΔG and positive value of ΔS showed that the adsorption of aniline onto NK and AK was feasible and spontaneous. The positive value of ΔH confirmed the endothermic nature of adsorption.