UBC Theses and Dissertations
Corrosion of lead anodes in metallic electrowinning environments Tunnicliffe, Matthew
The corrosion of anodes in electrowinning is costly because of their relatively short lifespan, material cost, and their impact on cathodic deposit quality. The objective of this thesis was to understand the corrosion behavior of Pb anodes in electrolyte simulating Zn and Ni electrowinning conditions. Pb-based alloys have been used because they are cheap, conductive and stable at high potential and low pH. Experiments in this thesis included open circuit potential (OCP), potentiodynamic, and potentiostatic polarizations. The parameters studied include; icorr, Ecorr, slope of the oxygen evolution region and O₂ potential. For Zn electrowinning, variables changes included modifying H₂SO₄, Mn²⁺, Cl⁻, Zn²⁺ concentrations and increasing temperature. The best corrosion resistance in Zn electrowinning was achieved by increasing H₂SO₄ concentration, using 15 g/L Mn²⁺, 0 g/L Cl⁻, and increasing both Zn²⁺ temperature. Corrosion products were studied using SEM and EDX and the relationship between surface morphology of the working electrode and operating potential. Deaerating the cell reduced the dissolved oxygen in the cell and generally increased icorr, oxygen evolution region slope and OER overpotential. For Ni electrowinning applications, three materials were used as cast PbAg, rolled PbAg, and as cast PbCaSn. The effects of H₂SO₄ and Cl- on corrosion behavior were studied using both potentiodynamic and galvanostatic polarizations. Corrosion rates were determined by measuring the length of the discharge peak after 24 hours galvanostatic polarization and SEM and XRD were used to determine the surface morphology and phase composition of the anodes.
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