Effect of solution components on stability of protective PbO2 layers on Pb-Ca-Sn anodes for copper electrowinning

Potential-time curves have been carried out in CuSO4-H2SO4 electrolytes to establish the effect of various impurities and additives on the stability of the protective PbO2 layer formed on Pb-Ca-Sn alloys used in copper electrowinning. The most important effects are those of guar and Fe(III). Acting separately, they tend to stabilise the protective layer, whereas Co(II) and Mn(II) do not. The effect of Fe(III) can be explained by its strong oxidising power; the effect of guar, by its ability to form a protective barrier of organic molecules adsorbed on the PbO2 layer. The effects of both guar and Fe(III) are diminished by the presence of other species in solution: reducing species diminish the effect of ferric ions and guar is degraded by oxidising species.