Comparative Study on Adsorption Isotherm and Kinetics of Defluoridation Using Aluminum and Iron Electrodes in Electrocoagulation

Adsorption equilibrium and kinetics of fluoride removal by aluminum and iron electrodes in electrocoagulation technology were investigated and compared in a batch reactor. Adsorption equilibrium for Al-EC and Fe-EC were conducted at a range of current density (J) 19–38 and 10–18.50 mA/cm2, respectively, while the treatment time was at a range of 15–60 min to study the adsorption kinetics. The surfaces of flocs produced were characterized using Fourier transform infrared spectroscopy. The adsorption equilibrium and kinetics of fluoride in both Al-EC and Fe-EC fitted well to the Freundlich model and pseudo second order. The removal mechanisms of fluoride were through ion exchange and electrostatic attraction in Al-EC and Fe-EC, respectively both occurred spontaneously and were physical in nature. The Al(OH)3 and Fe(OH)2 exhibited monolayer adsorption capacities of 131 and 0.08 mg/g, respectively. Thus, the Al(OH)3 in Al-EC is a better candidate for defluoridation compared to Fe(OH)2 of Fe-EC during electrocoagulation technology.