Removal of copper, zinc and nickel present in natural water containing Ca2+ and HCO3- ions by electrocoagulation

Electrocoagulation (EC) is an efficient technique for cleaning wastewater containing heavy metals before discharge in the environment. Studies on EC are usually conducted by adding supporting electrolyte to the medium investigated so as to increase the electrolyte conductivity and improve the sacrificial anodic dissolution of the electrodes. The present study was conducted with low-conductivity natural water (Grenoble tap water) artificially polluted with copper, zinc and nickel. It shows that addition of supporting salts is not necessary to obtain high removal efficiencies. For these metals, elimination rates above 95% were obtained after only 60 min of treatment, especially in the case of aluminum electrodes. These high removal efficiencies can be explained by the partial precipitation of copper and zinc before treatment owing to the highest pH value of natural water (compared with distilled water), by pH increase during EC caused by the reduction of water on the cathode, and by possible co-precipitation of calcium carbonate (formed from calcium and bicarbonate ions present in tap water) and metallic hydroxide species produced by the anodic dissolution of the electrodes. (C) 2013 Elsevier B.V. All rights reserved.