The removal of fluoride from aqueous solution by a lateritic soil adsorption: Kinetic and equilibrium studies

The use of natural sorbents to remove fluoride from drinking water is a promising alternative because of its low-cost and easy implementation. In this article, fluoride adsorption on a latosol soil from Misiones province (Argentina) was studied regarding kinetic and equilibrium aspects. Experiments were conducted in batch at room temperature under controlled conditions of pH 4-8) and ionic strength (1-10mM KNO₃). Experimental data indicated that adsorption processes followed a PSO kinetic where initial rates have showed to be influenced by pH solution. The necessary time to reach an equilibrium state had resulted approximately 30min. Equilibrium adsorption studies were performed at pH 8 which is similar to the natural groundwater. For that, fluoride adsorption data were successfully adjusted to Dubinin-Ataskhov model determining that the fluoride adsorption onto soil particles mainly followed a physical mechanism with a removal capacity of 0.48mgg^-1. Finally, a natural groundwater was tested with laterite obtaining a reduction close to 30% from initial concentration and without changing significantly the physicochemical properties of the natural water. Therefore, it was concluded that the use of lateritic soils for fluoride removal is very promising on a domestic scale.