Study of the adsorption of fluoride in aqueous solution by eco-friendly cost-effective adsorbent: characterization and adsorption mechanism

Adsorption potential of Moroccan sodium bentonite clay was investigated for aqueous solution defluoridation using batch equilibrium experiments. The aim of this study was to evaluate the adsorption potential of the natural sodium bentonite clay for fluoride removal from aqueous solution and to explore the mechanism that might occur in the fluoride adsorption process. The compositional, structural and textural characteristics of the natural sodium bentonite clay were determined using accurate physicochemical and mineralogical characterizations. The contents of fluoride ions in aqueous solution were determined by the potentiometric method with a fluoride-specific ion electrode connected to a digital ion analyzer. The study and optimization of various operational parameters such as contact time, initial fluoride concentration, adsorbent dose and initial pH solution were carried out through batch adsorption experiments, conducted at room temperature. The experiments results showed that 30 min of contact time was sufficient for attaining equilibrium between the liquid and solid phases. The maximum aqueous solution defluoridation was noted to be 52.2% in the acidic conditions, and for 5 mg L -1 and 2 g L -1 of initial fluoride concentration and adsorbent dose, respectively. The experimental data followed pseudo-second-order and fitted well into Freundlich adsorption, indicating multilayer adsorption with heterogeneous energetic distribution of active sites