The Effect of Lead Impurity in Presence of Manganese Addition on Zinc Electrowinning

"Zinc electrowinning process is sensitive to the presence of metallic impurities such as lead ions that could substantially and negatively affect the power consumption and surface morphology. Effect of various concentrations of manganese ions and traces of lead ions up to 2.5 mg L-1 added to the electrolyte during electrowinning have been investigated by electrochemical polarization techniques such as galvanostatic, cyclic voltammetry and potentiodynamic. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to examine the surface morphology and crystallographic orientation, respectively. Microwave plasma-atomic emission spectrometry has been used to determine the lead content in the deposit and in the electrolyte after electrodeposition. It was found that lead ions added to the zinc electrolyte led to the increase of cathodic overpotential and current efficiencies of zinc deposit. However, addition of Mn2+ into the zinc electrolyte resulted in the decrease of cathodic potential and current efficiency of zinc deposit. It can be stated as example that galvanostatic polarisation at 40?C and 52.5 mA cm-2 in presence of lead up to 0.1-0.2 mg L-1 in the electrolyte and 8-12 g L-1 Mn could be better considered as practical working parameters for electrowinning process.INTRODUCTIONApproximately 85% of the global production of zinc metal is produced by electrolytic process (Sinclair, 2005). The main goal of the zinc plant is to obtain pure zinc deposits with high current efficiencies. Smooth and pure deposits with high current efficiency (CE) are always obtained from pure electrolytes (Alfantazi & Dreisinger, 2001). The presence of metallic impurities in the zinc sulphate electrolyte is a major problem for the zinc electrowinning industry, since decreases in current efficiency, changes in deposit morphology and cathodic polarization are observed for electrolytes containing small concentrations of impurities (Ault & Frazer, 1988; Muresan, Maurin, Oniciu & Gaga, 1996). Low level concentrations as parts per million of these impurities are reported to influence negatively the zinc electrodeposition (Beshore, Flori, Schade & O'Keefe, 1987)."