Influence of manganese on the electrochemical behavior of an aluminum cathode used in zinc electrowinning

Pure aluminum is commonly used as the cathode electrode in the traditional hydrometallurgy applications of zinc electrowinning. However, with the decrease of zinc concentrate grade and increase of the impurity ions in the electrolyte, the corrosion consumption of the cathode material increases gradually. To further improve the corrosion resistance and electrocatalytic activity of the aluminum cathode, the electrochemical behavior of manganese as an additive for pure Al cathode material, such as Al-Mn alloy, was studied herein. Using the analysis methods of electrochemical impedance spectroscopy, cathodic polarization, galvanostatic polarization, and Tafel curves, the effect of Mn content on the electrochemical behavior of Al-Mn alloy in 40℃ constant temperature conditions and a solution containing Zn²⁺ at 65 g·L^-1 and H₂SO₄ at 150 g·L^-1 was investigated. The results show that the corrosion resistance of Al alloy containing Mn increases obviously compared to that of pure Al electrodes, and the increase of the Mn content could decrease the corrosion current. Moreover, the corrosion potential and the Mn content do not exhibit obvious change trends. When the Mn content reaches 1.5%, the corrosion current reaches the lowest value of 1.11 mA·cm^-2 and the corrosion potential reaches the minimum of -1.0954 V. When the electrical potential of cathode becomes zero, the exchange current density is influenced by the Mn content and the exchange current density i₀ exhibits an initial increasing trend and then declines with the increase of the Mn content. When the Mn content is 1.5%, the exchange current density of the Al alloy cathode reaches the maximum of 3.7462×10^-16 mA·cm^-2; this value is much higher than that of the pure Al electrode (4.8027×10^-33 mA·cm^-2). The overall change amplitude is obvious, and the electrocatalytic activity of the Al-Mn electrodes is much improved compared with a pure Al electrode. The electrochemical process is controlled by the electrochemical mass transfer. Considering the corrosion resistance and electrocatalytic activity of the electrode material, the Al-Mn alloy containing 1.5% of Mn can be used as an ideal electrolytic zinc cathode.