Abstract
Heavy metals are found as pollutant in many industrial waste waters. The toxicity of heavy metals has been known for many years and they belong to persistent toxic substances. Therefore, removal of these metals from industrial effluents represents an important challenge in order to avoid one of the major causes of water and soil pollution. The aim of this thesis was the efficient removal of two metal ions which are close to or more noble than hydrogen in the electromotive series (i. e. zinc and copper) from aqueous solutions that simulate industrial wastewater containing these two elements. The removal was done by employing an electrolytic reactor, provided with a 3-dimensional packed-bed cathode of carbon particles, operated in a continuous recirculation mode of flow. Firstly, the removal of copper from monometallic solution was dealt with where the effects of initial concentration of the metal, flow rate, applied current intensity and initial pH (pHo) on removal % and current efficiency of the metal removal were presented. Moreover, two experiments were performed at the same recirculation flow rate, pHo and initial concentration. In the first one the applied current was fixed at 7 A, while in the second one the applied current was decreased from 7 A to 3 A; by manually decreasing 1A every 15 minutes. The second mode of current application led to saving of 41.6 % in the electrical energy utilized for about 96 % removal of copper. Also, the removed copper could be recovered as Cu2O. Secondly, the removal of copper and zinc from bimetallic solutions - containing different mass ratios of Cu to Zn in the range from 0 - 80 % - were investigated. Experiments were carried out under galvanostatic condition. The initial pH was kept almost constant at a nominal value of 2.65 and the rate of flow of the treated solution was fixed at 0.065 L/s. It was found that: - The increase of Zn ratio did not affect the removal of copper negatively; but the presence of Cu with Zn did. - Increasing applied current intensity enhanced the removal of Cu and Zn while the current efficiency was decreased. - The effects of generation of hydrogen, anodic dissolution and IR drop are main reasons for decreasing current efficiency. Thirdly, a kinetic study was carried out in order to determine the order of the kinetics of metal-removal process and to shed light on how the operating parameters affect the value of rate constant. The study revealed that: - The removal of copper and Zn ions followed first order kinetics with respect to the concentration of the metal. - The apparent rate constant, k, of copper removal was found to depend on (F.R.), (pHo), (Co)Cu, (I) and the presence of Zn in the same solution with Cu. - The apparent rate constant, k, of Zn removal was found to be almost independent of the mass ratio of copper to zinc and increased with increasing applied current.