Extraction of Fluoride from Polluted Waters Using Low-cost Active Carbon Derived from Stems of Acalypha indica Plant

Abstract

Batch mode adsorption experiments have been conducted successfully for the removal of fluoride from polluted waters with nitric acid active carbon derived from stems of Acalypha indica plant (NAcIC). The effect of various parameters such as pH, sorbent dosage, agitation time, initial concentration of fluoride, temperature, particle size and presence of foreign ions have been studied in detail and optimized for the maximum extraction of fluoride. Adsorption data have been modelled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms and it has been observed that Langmuir isotherm well describes the experimental data because of R_L and highest R² values. Further, the Dubinin-Radushkevich mean free energy (E = 3.16 kJ/mol) and Temkin heat of sorption (B = 0.210 J/mol) for the NAcIC indicates the physisorption. Further, the adsorption kinetics is found to be pseudo-second order rate mechanism followed by pseudo-first order, intra particle diffusion, pore diffusion and Elovich model. FTIR, SEM and EDX studies confirm the fluoride binding ability of adsorbent. Field studies have been carried out with the fluoride-contaminated groundwater samples in order to test the suitability of the NAcIC using the same methodology at field conditions and it is found to be remarkably successful.