Electrochemical analysis of the simultaneous electrolysis of zinc and manganese dioxide in zinc electrowinning system

In this work, the electrochemical process of the simultaneous electrolysis of zinc and manganese dioxide was systematically analyzed based on cyclic voltammetry, linear voltammetry, and electrochemical impedance spectroscopy, combined with electrolytic experiments. The results show that the reduction of Zn²⁺ and the oxidation of Mn²⁺ in the system do not interfere with each other within a Mn²⁺ concentration lower than 10 g/L. Increasing the concentration of Mn²⁺ is beneficial for electrolysis in the same cell. However, if the concentration of Mn²⁺ is too high, it will increase the generation of oxidizing MnO₄^-, leading to the dissolution of cathode Zn by chemical oxidation;The electro-oxidation process of Mn²⁺ is affected by the passivation of the electrode interface. Increasing the concentration of Mn²⁺ is favorable to the same groove electrolysis. However, an over-high concentration of Mn²⁺ will increase the production of oxidative MnO₄^-, resulting in the dissolution of the cathode Zn by the chemical oxidation. In addition, increasing the deposition temperature can improve the same groove electrolysis performance of Zn-MnO₂, but an excessively high temperature (≥ 80 ℃) will accelerate the corrosion of Zn. The optimal conditions of same groove electrolysis of Zn and MnO₂ are as follows: Mn²⁺ concentration is 10 g/L, with a cathode current density of 40 mA/cm² and an anode current density of 10 mA/cm², respectively, at a temperature of 60 ℃. In the optimal conditions, cathode and anode current efficiencies are 94.81% and 12.16%, respectively. The energy consumption per ton of zinc is 2 456.58 kW·h, and the anodic product isε-MnO₂.