Removal of fluoride from an aqueous solution by using montmorillonite Original Research Article

The removal of fluoride from aqueous solution by using montmorillonite was studied by a batch equilibration technique. Influence of contact time, pH, initial fluoride concentration and adsorbent dosage on the adsorption were investigated. It was found that the sufficient time for adsorption equilibrium of fluoride ions is 180 min. The maximum removal of fluoride ion was obtained at pH 6. The mechanism for fluoride removal was explained by considering the interaction between the metal oxides at the surface of montmorillonite and fluoride ions. The adsorption isotherms were analyzed using the Langmuir, the Freundlich, and the three-parameter Redlich–Peterson isotherms. In order to determine the best-fit isotherm, two error analysis methods, the linear coefficient of determination and the Chi-square statistic test for determination of a non-linear model, were used to evaluate the data. According to the error analysis, both Freundlich and Redlich-Peterson isotherm models were found to represent the measured sorption data well. The adsorbed fluoride could be easily desorbed by washing the adsorbent with a solution pH of 12.