Revealing the Reaction Mechanism of Lead Anodes in the Manganese Electrowinning Process

The electrowinning process of metal manganese suffers from the generation of anode slime. The solution has been hampered by a lack of clarity in the reaction mechanism. In this work, the anodic process was investigated from three aspects. First, four time points were selected to study the self-oxidation of the lead anode; second, the electrochemical behavior of manganese ions was observed by in situ UV–Vis spectroscopy; and finally, the chemical states of oxidative products and their effects on oxygen evolution were analyzed via X-ray photoelectron spectroscopy (XPS) and Tafel curves. Results show that an oxide film is formed on the inner side by self-oxidation of the lead anode and the manganese dioxide in the system is produced by the hydrolysis of trivalent manganese ions. A lead matrix/lead sulfate/lead–manganese mixed layer/nano-manganese dioxide layer is gradually formed on the surface. As the electrolysis progresses, the oxygen evolution activity of the electrode gradually increases, but the anode film tends to fall off under the wash of oxygen. The final anode slime is formed by the mixture of hydrolysates in the solution and the falling anode film. This work is expected to lay a theoretical framework for the anodic research of electrolytic manganese.