Insights into cationic methyl violet 6B dye-kaolinite interactions: Kinetic, equilibrium and thermodynamic studies

In this study, adsorption and adsorption kinetics of methyl violet dye from aqueous solutions onto kaolinite were investigated. The effects of adsorbent dosage, pH, ionic strength, contact time, temperature and initial dye concentration were studied. Kinetic and thermodynamic parameters were determined using experimental data. Adsorption capacity decreased with increasing ionic strength. Changes in the initial pH of the dye solution in a range close to the dye's natural pH (i.e. ∼ pH 5.0) values affected adsorption capacity slightly, indicating that adsorption studies could be carried out at the dye's natural pH. The adsorption process followed the Freundlich-type adsorption isotherms and pseudo-second order type adsorption kinetics. However, an intraparticle diffusion process was found to have effects in adsorption processes. Thermodynamic parameters were calculated from the experimental data and enthalpy of the adsorption, AH0, was found to be -6.82 kJ moP, indicating physisorption nature of the adsorption. Other thermodynamic parameters, AS and DG0, were also calculated. Negative values of AG0 indicated that the adsorption process for methyl violet on kaolinite is spontaneous. © 2013 The Mineralogical Society.