Water defluoridation by alumina modified Turkey clinoptilolite: equilibrium, kinetic models and experimental design approaches

In the current work, alumina modified natural zeolite (Z-Al) was used for fluoride adsorption in aqueous solution. Effects of process parameters such as pH, temperature, initial concentration and contact time were investigated. Box-Behnken design was found effective in defining the operating conditions for fluoride sorption onto Z-Al. Confirmatory experiments were conducted to examine the reliability of the regression equation. The predicted (2.261 mg g(-1)) and experimental (2.289 mg g(-1)) capacities were found to be similar, demonstrating the accuracy of the model. The fluoride adsorption onto Z-Al was well described by the Freundlich model. Kinetic studies revealed that the adsorption followed a pseudo-second-order reaction. Thermodynamic parameters depicted that the fluoride adsorption on the alumina modified zeolite was a spontaneous and exothermic process. The co-existing ions affected the defluoridation performance significantly. Regeneration of exhausted Z-Al was achieved with H2SO4.