Electrochemical investigation of electrolyte composition and electrolysis parameters during zinc electrowinning

Abstract

The effect of different Mn2+ and Pb2+ concentrations added to the zinc sulfate acid electrolyte during zinc electrowinning process was investigated. Operating parameters such as zinc ion concentration, acid concentration, current density, electrolyte agitation, and temperature were investigated in the presence of Mn2+ and Pb2+. Galvanostatic polarization, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy studies were performed to examine the cathodic behavior. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the surface of the zinc deposit. The addition of lead ions to the zinc electrolyte led to an increase in the cathodic potential and current efficiencies of the zinc deposition. The addition of Mn2+ to the zinc electrolyte resulted in a decrease in the cathodic potential and current efficiency of zinc deposition. An increase in the current density from 45 to 60 mA cm−2 and in electrolyte agitation from 60 to 412 rpm resulted in an increase in the cathodic potential and decrease in current efficiencies. A temperature increase from 35 to 45 °C led to a decrease in the cathodic potential. After a short initial electrodeposition (2–4 h) using a Pb–0.7%Ag anode, the lead content in the zinc deposit was higher than that obtained with a Pt anode (0.15 mg L−1 Pb2+). A long deposition period of more than 72 h was also considered, and Pb content was almost the same in the zinc deposit for Pb2+ quantities (0.15 or 0.2 mg L−1).