Enhanced fluoride adsorption by nano crystalline γ-alumina: adsorption kinetics, isotherm modeling and thermodynamic studies

Nano materials in particular nano oxides with enhanced surface area and an excellent catalytic surface serve as potential adsorbents for defluoridation of water. In the present study nano gamma-alumina was synthesized through a simple and low cost, surfactant assisted solution combustion method. As synthesized material was characterized by XRD and FESEM for its phase, size and morphological characteristics. Surface properties have been investigated by BET method. Nano gamma-alumina was further used for a detailed adsorption study to remove fluoride from water. Batches of experiments were performed at various experimental conditions such as solution pH, adsorbent dose, initial fluoride concentration and contact time to test the defluoridation ability of gamma-alumina. Fluoride Adsorption by nano sized gamma-alumina was rapid and reached equilibrium within two hours. The adsorption worked well at pH 4.0, where similar to 96 % of fluoride was found to be adsorbed on adsorbent. It was possible to reduce fluoride levels to as low as 0.3 mg/L (within the safe limit of WHO: <= 1.5 mg/L) from an initial fluoride levels of 10 mg/L. This could be achieved using a very small quantity, 1 g/L of gamma-alumina at pH 4 within 1 h of contact time. Defluoridation capacity of nano gamma-alumina was further investigated by fitting the equilibrium data to various isotherm as well as kinetic models. The present study revealed that gamma-alumina could be an efficient adsorbent for treating fluoride contaminated water.