External mass transport process during the adsorption of fluoride from aqueous solution by activated clay

Abstract

The removal of fluoride ions from an aqueous solution using a modified sulfuric acid clay was studied in batch adsorption. The adsorption kinetics were studied to identify the retention mechanisms. For kinetics study, perfectly stirred batch experiments were carried out after the adjustment of the parameters influencing the system, such as the pH, the adsorbent dosage, the initial concentration of fluoride ions, and the stirring speed. It appears that the rate of fluoride ion removal (1) increased with the mass of adsorbent and the stirring speed, and (2) decreased with the initial fluoride ion concentration. The experimental results were adjusted according to kinetic equations representing four external transport models. The latter were used to calculate the external mass transfer coefficient, k f . The results showed that this coefficient is in the range of 10 −5 –10 −4 m s −1 .