UBC Theses and Dissertations
Lowering the energy consumption of zinc electrowinning by electrocatalysis of the oxygen evolution reaction using manganese oxides Arfania, Sheida
Zinc is employed in a wide range of commercial applications including galvanizing iron and steel and production of various metal alloys. In hydrometallurgical processes, zinc electrowinning from sulfate-based electrolytes is the last step of zinc extraction in which high purity metallic zinc is electrodeposited from a highly acidic solution on an aluminum cathode. The electrowinning stage is very energy-intensive and responsible for approximately 60% of the power requirement of a zinc refinery. Inside the electrowinning cell, oxygen evolution reaction (OER) overpotential on conventional lead-silver (Pb-Ag) anodes contributes to nearly 25% of the overall cell potential and places a heavy financial burden on zinc refining plants. Thus, improving the energy efficiency of electrowinning by lowering the OER overpotential is of primary significance to the zinc refineries. This study aimed to develop and evaluate novel anodes in order to lower the OER overpotential within the zinc electrowinning process. The novel anodes were prepared by electrodeposition of manganese oxides (MnOx) on industrially provided Pb-Ag substrate using various potentiodynamic and galvanostatic polarization techniques. The anodic electrocatalytic activity of the baseline and MnOx electrodeposited Pb-Ag electrodes was investigated in a manganese (II)-containing sulfuric acid electrolyte using linear scan voltammetry and 72-hour galvanostatic electrolysis at 500 amperes per meter squared current density. Additionally, the baseline and novel anodes were studied within the full-cell electrowinning setup by the means of 24-hour galvanostatic electrolysis at 500 amperes per meter squared current density. The electrolyte composition and operating conditions were selected such that to be directly applicable to the industrial zinc electrowinning process. The MnOx electrodeposited Pb-Ag anodes reduced the OER overpotential by a maximum of 155 and 113 mV in the absence and presence of chloride ions. Investigation of the novel electrodes in the full-cell zinc electrowinning operation corroborated the half-cell experiments, revealing a maximum of 133 mV reduction in overall cell potential. The surface morphology and elemental composition of the novel anodes were investigated using SEM/EDX, XRD, and ICP-OES. This work demonstrated that the MnOx electrodeposited Pb-Ag anodes reveal improved electrocatalytic activity and have great capacity to lower the energy consumption of the conventional zinc electrowinning process.
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