Removal of fluoride from polluted waters using active carbon derived from barks of Vitex negundo plant

Abstract

Abstract Background Deleterious effects of fluoride contamination in ground waters on the health of human beings are well known and intensive research on developing de-fluoridation methods is globally pursued. Of the various methodologies, increasing interest is being envisaged in using the adsorption methods based on active carbons derived from plant material. In the present investigation, Nitric acid activated carbon derived from barks of Vitex negundo plant (NVNC) is probed for its de-fluoridation abilities. Methods The activated carbon is characterized adopting various physicochemical methods and surface morphological studies are carried out using FT-IR and SEM-EDX techniques. The effect of various parameters such as pH, sorbent dosage, agitation time, initial concentration of fluoride, temperature, particle size and presence of foreign ions on the extraction of the fluoride is studied adopting Batch methods.The adsorption process is analyzed with Freundlich, Langmuir, Temkin and Dubinin-Radushkevich (D-R) isotherms and kinetics of adsorption is studied using pseudo first-order, pseudo second-order, Weber and Morris intraparticle diffusion, Bangham’s pore diffusion and Elovich equations. The methodology developed is applied to real ground water samples. Results De-fluoridation is maximum at the pH: 7.0, adsorbent dosage: 4.0g/lit; equilibrium time: 50 min, Particle size: 45μ and temperature: 30 ± 1°C. The correlation coefficient values for the adsorption isotherms: Freundlich, Langmuir, Temkin and Dubinin-Radushkevich are 0.929, 0.998, 0.980 and 0.946 respectively and for kinetic models: pseudo-first-order, pseudo-second-order, Weber and Morris intraparticle diffusion, Bangham’s pore diffusion and Elovich equations are 0.989, 0.994, 0.874, 0.902 and 0.912 respectively. The Temkin heat of sorption, B, and the Dubinin-Radushkevich mean free energy, E, for the activated carbon adsorbent are 0.196 J/mol and 7.07 kJ/mol respectively. Conclusions Nitric acid activated carbon derived from barks of Vitex negundo (NVNC) plant is found to be an effective adsorbent for the de-fluoridation of waters. The adsorption process is satisfactorily fitted with Langmuir adsorption isotherm with good correlation coefficient value and it indicates monolayer adsorption. The adsorption kinetics is found to follow pseudo-second-order kinetics. The Dubinin-Radushkevich mean free energy and Temkin heat of sorption confirm the physisorption nature as these are lower than 20kJ/mol. The procedure developed is remarkably successful in de-fluoridation of real ground water samples.