Georges Houlachi

Effect of Gelatin and Antimony on Zinc Electrowinning by Electrochemical Noise Measurements

Abstract The influence of an additive (gelatin), impurity (antimony) or a combination of both gelatin and antimony on zinc electrowinning in sulphuric acid electrolytes was investigated by electrochemical noise measurements. This study was oriented to examine the utility of using electrochemical noise (EN) technique to characterize the electrowinning process and the deposit structure morphology during electrolysis and complement the scanning electronic microscope studies (SEM). The electrochemical noise analysis in the time domain (skewness and kurtosis parameters) was successful in revealing the combined effect of different concentrations of gelatin and antimony on zinc electrowinning process. Skewness and kurtosis slope values around 0 mean that the distribution ofthe data is symmetric around the mean value and that the shape is similar to that of the normal distribution and seemed to correspond to the best combination of the synergetic effect of impurity and additive for higher current efficiency, lower overpotentials, better smooth and compact deposits.

Electrochemical behavior of mesh and plate oxide coated anodes during zinc electrowinning

Abstract The catalytic performance of two oxides coated anodes (OCSs) meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 °C. Their electrochemical behaviors were compared with that of a conventional Pb–0.7%Ag alloy anode. Electrochemical measurements such as cyclic voltammetric, galvanostatic, potentiodynamic, open-circuit potential (OCP) and in situ electrochemical noise measurements were considered. After 2 h of OCP test, the linear polarization shows that the corrosion current density of the Ti/(IrO2–Ta2O5) mesh electrode is the lowest (3.37 μA/cm2) among the three OCAs and shows excellent performance. Additionally, after 24 h of galvanostatic polarization at 50 mA/cm2 and 38 °C, the Ti/MnO2 mesh anode has the highest potential (1.799 V), followed by the Ti/(IrO2–Ta2O5) plate (1.775 V) and Ti/(IrO2–Ta2O5) mesh (1.705 V) anodes. After 24 h of galvanostatic polarization followed by 16 h of decay, the linear polarization method confirms the sequence obtained after 2 h of OCP test, and the Ti/(IrO2–Ta2O5) mesh attains the lowest corrosion current density. The Ti/(IrO2–Ta2O5) mesh anode also shows better performance after 24 h of galvanostatic polarization with the overpotential lower than that of the conventional Pb–Ag anode by about 245 mV.

Monitoring the Influence of Gelatin and Thiourea on Copper Electrodeposition Employing Electrochemical Noise Technique

Abstract The copper electrodeposition from sulphuric acid electrolytes in the presence of thiourea and gelatin as additives was investigated using Electrochemical Noise (EN) and Linear Sweep Voltammetry (LSV) in conjunction with the scanning electron microscopy technique. This study was oriented to examine the utility of using EN technique to characterize the electrowinning process and the deposit structure morphology was compared to LSV, an electrochemical method generally used industrially. Both EN and LSV techniques were successful in revealing the effect of different concentrations of thiourea and gelatin on the copper electrodeposition process. In this study, LSV detected an excess of thiourea leading to porous deposit; while the EN analysis in the time domain (skewness and kurtosis parameters) detected the presence of nodules and has provided useful information concerning the morphology of the deposit closely related to the macroscopic and microscopic studies.

Influence of silver content and MnSO4 addition on performance of different lead–silver alloys during polarisation and decay periods

Abstract The electrochemical activity and the corrosion properties of five commercial lead anodes were examined by the conventional polarisation methods and the electrochemical impedance spectroscopy method. The results show that the anode Pb–0·62Ag alloy had a lower overpotential for anode reaction than the others. The corrosion resistance after polarisation of the anode Pb–0·62Ag alloy was higher than that of the Pb–0·29Ag–0·1Ca alloy, Pb–0·58Ag alloy and Pb–0·67Ag alloy, but lower than that of the anode Pb–0·72Ag alloy. However, the anode Pb–0·72Ag alloy had the highest overpotential. When anodes Pb–0·72Ag alloy and Pb–0·62Ag alloy were used, the cathode current efficiencies were higher, while anodes Pb–0·29Ag–0·1Ca alloy, Pb–0·58Ag alloy and Pb–0·67Ag alloy gave lower current efficiency. Regarding these several factors, the anode Pb–0·62Ag alloy is the best choice. On a examiné l’activité électrochimique et les propriétés de corrosion de cinq anodes commerciales en plomb, au moyen des méthodes conventionnelles de polarisation et de la méthode de spectroscopie d’impédance électrochimique. Les résultats montrent que l’anode de Pb–0·62Ag avait une surtension plus basse que celle des autres pour la réaction de l’anode. La résistance à la corrosion après la polarisation de l’anode de Pb–0·62Ag était plus élevée que pour l’anode de Pb–0·29Ag–0·1Ca, l’anode de Pb–0·58Ag ou l’anode de Pb–0·67Ag, mais plus basse que celle de l’anode de Pb–0·72Ag. Cependant, l’anode de Pb–0·72Ag avait la surtension la plus élevée. Lorsqu’on utilisait les anodes de Pb–0·72Ag ou de Pb–0·62Ag, le rendement du courant de la cathode était plus élevé, alors que les anodes de Pb–0·29Ag–0·1Ca, de Pb–0·58Ag et de Pb–0·67Ag donnaient un rendement de courant plus bas. Par rapport aux divers facteurs, l’anode de Pb–0·62Ag constitue le meilleur choix.