Electrocoagulation in the dual application on the simultaneous removal of fluoride and nitrate anions through respective adsorption/reduction processes and modelling of continuous process

Abstract

Electrocoagulation (EC) is known as an electrochemical process for the efficient removal of various pollutants including fluoride and nitrate anions. Continuous electrocoagulation (CEC) was applied to synthetic aqueous solutions containing mixtures of nitrate and fluoride anions both at initial concentrations of 0.1 g L−1 for simulation of effluents arising from the etching process in microelectronic industries. Several parameters such as electrode material, pH, current density, initial concentration as well as the presence of co-existing ions were studied. Without addition of an electrolyte, the optimizing conditions were found for aluminum electrodes at pH = 5.94, current density of 9.09 mA.cm−2 and distance between electrodes of 18 mm, leading to removal rates of 42.83% and 88.28% for nitrate and fluoride anions, respectively. The isolated electrogenerated solids were characterized by Energy Dispersion Spectroscopy (EDS) coupled to SEM, FT-IR, XRD, XPS, TGA and Raman spectroscopy. All the characterizations agree with the removals of nitrate and fluoride anions by reduction and adsorption, respectively. The anode and the cathode were involved, but the reduction and adsorption processes were independent of each other. The nitrate reduction was a cathodic reaction leading to hydroxide anions which were involved in the formation of electrogenerated adsorbents by reaction with the aluminum cations (or metal cations) arising from the anode oxidation. A modelling kinetic theory for a continuous electrocoagulation process was developed and applied to the treatment of artificial and real wastewaters. The treatment cost of the real wastewater was found at 2.3097 USD per m3.