Removal of heavy metal ions from aqueous solution by electrocoagulation using a horizontal expanded Al anode

Abstract

The performance of a batch cell with a horizontal expanded Al-anode in removing Cu2+ and Cr from a hexavalent chromium solution by electrocoagulation from separate solutions was examined. The effect of electrolysis time, current density, pH, initial pollutant concentration and NaCl concentration on the removal efficiency of Cu2+ and Cr has been investigated. The results revealed that as current density increases the removal efficiency of Cu2+ increases, while in the case of Cr it increases up to a certain limit, then remains approximately constant. The optimum pH is from 4 to 6 and 3.5 for Cu2+ and Cr removal, respectively. The removal efficiency of Cu2+ increases as NaCl increases, but in the case of Cr it decreases. COD measurements showed that a 66.67% reduction of COD has been obtained at the optimum conditions of Cu2+ removal. Energy consumption was calculated for both heavy metals at different current density and NaCl concentration. At the optimum condition an energy consumption of 43 kWh is required for the removal of one kg of Cu2+ ions; a value of 145 kWh is required for the removal of one kg of Cr. The difference in behavior between Cu2+ removal and Cr removal was explained on the basis that cathodic reduction of Cr6+ to Cr3+ which controls the rate of Cr removal.