Fluoride Removal from Water with Spent Catalyst

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Abstract
The adsorption of fluoride from water with spent catalyst was studied. Adsorption density of fluoride decreased with increasing pH. Linear adsorption isotherm was utilized to describe the adsorption reaction. The adsorption was a first-order reaction, and the rate constant increased with decreasing surface loading. Adsorption reaction of fluoride onto spent catalyst was endothermic, and the reaction rate increased slightly with increasing temperature. Fluoro-alumino complex and free fluoride ion were involved in the adsorption reaction. It is proposed that both the silica and alumina fractions of spent catalyst contribute to the removal of fluoride from aqueous solution. Coulombic interaction is proposed as the major driving force of the adsorption reaction of fluoride onto spent catalyst.