Effect of manganese (II) added to the electrolyte on the properties of lead anodes used in oxidation of ferrous sulphate to ferric sulphate

The present paper deals with the possibilities of increasing the corrosion resistance of lead anodes during anodic oxidation of ferrous sulphate to ferric sulphate. This was achieved by preliminary passivation of lead anodes in a sulphuric acid and ferrous sulphate solution to which manganous sulphate was introduced. Owing to the passivation of lead anodes by the 20 mA cm^–2 current a potential of 2.2 V vs SEH is established and on their surface, apart from PbO₂, MnO₂ is also formed. On the basis of voltametric measurements of lead anode oxidation, analysis of potential variations during their selfdepassivation, X-ray microanalysis and scanning analysis of the passivated electrode surface the role of MnO₂ in increasing the corrosion resistance in sulphuric acid solutions containing ferrous sulphate was determined. Also a mechanism explaining the effect of MnO₂ formed on the lead anode surface on limitation of the destruction process of the passive oxide layer during oxidation of the ferrous to ferric ions was suggested.