Adsorption of methylene blue from aqueous solution by kaolin and zeolite

In the present study, kaolin and zeolite have been utilized as adsorbents for the removal of a cationic dye, methylene blue (MB), from aqueous solution within a batch process. Characterization of the two adsorbents was carried out by nitrogen adsorption–desorption experiments (specific surface area measurements by the BET method). The effects of various parameters such as initial MB concentration, contact time, adsorbent concentration, stirring speed, solution pH and salt concentration were examined and optimal experimental conditions were determined. The kinetic data were analyzed using pseudo-first-order and pseudo-second-order models. The mass transfer model in terms of interlayer diffusion was applied to the experimental data to examine the mechanisms of the rate controlling step. In order to determine the best-fit-isotherm, the experimental data were analyzed by the Freundlich, Temkin, and Dubinin–Radushkevich equation which are found to best represent the equilibrium data for kaolin and zeolite. The values of activation parameters such as free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were also determined. The results indicate that kaolin and zeolite could be interesting alternative materials with respect to more costly adsorbents used for dye removal.