Electrowinning of Non‐Noble Metals with Simultaneous Hydrogen Evolution at Flow‐Through Porous Electrodes: I . Theoretical

This paper presents an interpretation of the experimental results obtained on the electrowinning of zinc at a flowthrough porous electrode in light of a mathematical model which was presented in Part I. The process is accompanied by simultaneous hydrogen evolution within the electrode, which increases the pore electrolyte resistivity and decreases the coulombic efficiency. We measured polarization curves, coulombic efficiencies, and current distributions under various conditions of zincate concentrations, flow rates, cell current, and electrode thickness. Reasonable agreement between the measured and predicted current distributions was obtained only under conditions of high electrolyte flow rates, low cell currents, and thinner electrodes. The deviations observed at low electrolyte flow rates and high cell currents are attributed to the agitating effects of the hydrogen gas bubbles, which enhance the local mass-transfer coefficient. This effect was not incorporated in the model due to the absence of adequate correlations.