Removal of crystal violet and acid green 25 from water using kaolin

The adsorption performances of crystal violet (CV) and acid green 25 (AG 25) from water by using kaolin (KM 20 and KM 40) were investigated. Batch adsorption kinetic and adsorption isotherm experiments were carried out. The fitted models were plotted and analyzed for adsorption kinetic and isotherm studies based on the experimental data obtained. For adsorption kinetics, pseudo-second-order kinetic model was best fitted. For CV, the R² values obtained were 0.9990 and 0.9995 for KM 20 and KM 40, respectively. For AG 25, the R² values obtained were 0.9971 and 0.9991 for KM 20 and KM 40, respectively. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models were plotted and investigated for the adsorption equilibrium studies. Among the isotherm models, Langmuir model was best fitted, thus indicating monolayer adsorption had occurred. For CV, the maximum adsorption capacity (q_max) values obtained were 23.64 mg/g and 31.35 mg/g for KM 20 and KM 40, respectively. For AG 25, q_max values of 23.26 mg/g and 30.49 mg/g were obtained for KM 20 and KM 40, respectively. In addition, the effect of solution pH was assessed. The qmax was obtained at pH 11 for CV and pH 7 for AG 25. (paper)