Fluoride removal from water by electrocoagulation: Effect of the type of water and the experimental parameters

Contamination of the ground water with fluoride is a great problem worldwide. Removal of fluoride (F-) ions from simulated natural waters containing fluoride by electrocoagulation (EC) using aluminum electrodes, has been investigated in a discontinuous lab cell. Two types of water have been studied: local tap water and deionized water-based luoride solutions of sodium fluoride with addition of sodium chloride to reach the desired conductivity. The effect of four operating parameters has been followed for a current density fixed at 5 mA/cm(2) within the following ranges: fluoride concentration (5-50 mg/L), temperature (25-55 degrees C), conductivity (1-6 mS/cm) and initial pH (4-8.5). In accordance with published data, the presence of 61 mg/L buffering hydrogencarbonate ions in the tap water was found to substantially reduce the Al(III) amount required for a given abatement in comparison with deionized water. Performance comparison of the discontinuous electrocoagulation treatment between the two types of water has been discussed for 90% abatement of F- introduced, in terms of the amount of Al(III) dissolved over the initial fluoride concentration, the parameters of a previous adsorption model and the fraction of Al(III) flocs not involved in the adsorption. EC performances were shown to be governed by the solution pH for the two types of water, with little effect of the other operating conditions: at initial pH 6, F- abatement was found to require two or three times less trivalent aluminium than at initial pH 8.5. (C) 2019 Elsevier Ltd. All rights reserved.