Adsorption of Fluoride from Water Using Aluminum Coated Sand: Kinetics, Equilibrium, Effect of pH, and Coexisting Ions

Abstract

An aluminum coated sand (AlCS) was evaluated as a metal oxide adsorbent for adsorption and removal of fluoride from water using a low-cost adsorbent with potential application in continuous flow adsorber systems. Surface characterization of the AlCS sorbent was performed using TEM, SEM/EDX, XRD and BET. The AlCS sorbent contained mostly amorphous aluminum oxides based on adsorbent characterization results. Favorable adsorption of fluoride onto the AlCS sorbent occurred according to the Langmuir and Freundlich adsorption equations, while physical adsorption of fluoride onto the AlCS sorbent was observed based on results from the Dubinin-Radushkevich equation. Fluoride adsorption onto the AlCS sorbent followed pseudo-second order kinetics, while surface charge analysis indicated a pHPZC of 7.1 for the AlCS sorbent. Effective fluoride removal occurred over a broad pH range from 3 to 11 with a maximum fluoride removal observed at pH 4 to 5. The effect of co-existing ions in water resulted in a decrease in fluoride uptake in the presence of bicarbonate, while resulting in an increase in fluoride uptake in the presence of calcium. The AlCS sorbent was a low-cost and sustainable adsorbent for effective adsorption and rapid removal of fluoride from water within an hour.