Effect of Current Densities on the Electrochemical Behavior of a Flat Plate Pb-Ag Anode for Zinc Electrowinning

Abstract

We studied the anodic potential,corrosion rate,and anodic passive layer of a flat plate Pb-Ag(0.8%(mass fraction,w) anode over a long period of polarization under different current densities.Additionally,the cathode current efficiency and quality of the zinc product in the ZnSO4-MnSO4-H2SO4 electrolyte were also studied.The morphology of the anodic passive layer was characterized by scanning electron microscopy(SEM).The results show that the current density greatly affects the electrochemical behavior of the anode and the cathode during zinc electrowinning irrespective of Mn2+.With an increase in the current density,the anodic potential,corrosion rate,cathode current efficiency,and quantity of anode slime increased while the Pb content in the zinc product decreased.When the current density decreased from 500 to 200 A·m-2 in the ZnSO4-MnSO4-H2SO4 electrolyte,the stable anodic potential and the corrosion rate decreased by 64 mV and 40%,respectively.Under a lower current density,the anodic potential stabilizes more easily and the passive layer that forms on the surface of the anode is denser and it adheres better to the base body,which is advantageous for the reduction of the corrosion rate.Therefore,to reduce the anodic potential,corrosion rate,and the quantity of anode slime,increase the cathode current efficiency and quality of zinc product,we suggested that the ideal working condition for zinc electrowinning is a higher cathodic current density and lower anodic current density.