Abstract: High fluoride concentration is a worldwide problem in drinking water due its health effects. Batch mode investigation to remove fluoride from aqueous solution and real groundwater samples by natural coal and its modified forms was made. The physicochemical analysis of adsorbents and their activation was overseen to well understand the mechanism of sorption. Adsorption was found to be pH dependent with optimal removal efficiency at pH 2 for physically and chemically activated coal and at pH 4 for natural coal (NC). The experimental data was well fitted with Langmuir and Freundlich adsorption model providing maximum adsorption capacity of 5.9, 8.36 and 11.35 mg/g for natural, physical and chemical activated coal in their order written from Langmuir model. The Dubinin–Radushkevich isotherm (R2 = 0.988) with mean free energy (E = 0.085 KJ/mol) for natural coal signify physiosorption should be mainly responsible for fluoride adsorption. The applicability of the adsorbents from fluoride contaminated groundwater indicated that natural coal (NC), physically activated coal (PAC) and chemically activated coal (CAC) can be used as an effective, low-cost adsorbent to remove fluoride from groundwater. The buffering capacity of adsorbents monitored during sorption induces a pH increase to nearly neutral, after sorption, which may be an important asset in real applications.
Keywords: Natural coal, Adsorption isotherms, Defluoridation.