Aluminum-cerium double-metal impregnated activated carbon: a novel composite for fluoride removal from aqueous solution

Several studies have focused on the application of layered double hydroxide or nanoparticle based adsorbent for removing fluoride. The objectives of this study are to impregnate aluminum (Al) and cerium (Ce) within the pore spaces of activated carbon (AC) for removal of fluoride from water and to evaluate the partitioning behavior of fluoride by the double-metal-AC composite. To achieve the objectives, combined oxides/hydroxides of Al and Ce were impregnated within the pore spaces of AC under varying pH, metal concentration, and synthesis temperature. The fluoride removal by different composite was evaluated, and the best performing composite was selected for equilibrium sorption experiments and kinetic tests. The effect of pH on fluoride removal was assessed. Overall it was observed that impregnation of a small amount of metal (0.05 mol/L Al-Ce) can enhance the fluoride removal efficiency, compared to unmodified AC. Sorption of the best performing composite follows the Freundlich isotherm model. The maximum fluoride sorption capacity was estimated as 3.05 mg F-/g of composite. The rate of sorption by the selected composite is reasonably fast (3.6/h). Furthermore, within a wide range of pH (5-10), removal of fluoride was observed to be consistent.