Adsorption of fluoride from aqueous solution by magnesia-amended silicon dioxide granules

BACKGROUND: A new kind of adsorbent, magnesia-amended silicon dioxide granules (MAS), has been prepared by wet impregnation of silicon dioxide with magnesium chloride solution. The physicochemical properties were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Brunauer, Emmett, Teller (BET) studies. The porous structure and high surface area of these granules make them suitable for sorption. The aim of this study was to show the possibility of defluoridation of water using MAS and to demonstrate the advantage of its use compared with silicon dioxide. RESULTS: XRD and FT-IR analysis showed that amorphous magnesia was loaded on silicon dioxide after treating with magnesium chloride solution and calcining at 500 degrees C. Batch sorption experiments indicated that MAS is more effective than silicon dioxide for fluoride adsorption. The sorption capacities of MAS decreased as the solution PH rose. At PH 3, the maximum defluoridation capacity of MAS was 12.6 mg g(-1). The adsorption process fitted the Dubinin-Radushkevich isotherm and kinetic studies revealed that the adsorption followed second-order rate kinetics. CONCLUSION: The results indicate that it is feasible to modify both the physical and chemical properties of silicon dioxide with magnesia so that it can be used as a potential adsorbent to adsorb fluoride from aqueous solution. (C) 2009 Society of Chemical Industry