ELECTROWINNING OF NONNOBLE METALS WITH SIMULTANEOUS HYDROGEN EVOLUTION AT FLOW-THROUGH POROUS-ELECTRODES .2. EXPERIMENTAL

This paper presents an interpretation of the experimental results obta ined on the electrowinning of zinc at a flow-through porous electrode in light of a mathematical model which was presented in Part I. The pr ocess is accompanied by simultaneous hydrogen evolution within the ele ctrode, which increases the pore electrolyte resistivity and decreases the coulombic efficiency. We measured polarization curves, coulombic efficiencies, and current distributions under various conditions of zi ncate concentrations, flow rates, cell current, and electrode thicknes s. Reasonable agreement between the measured and predicted current dis tributions was obtained only under conditions of high electrolyte flow rates, low cell currents, and thinner electrodes. The deviations obse rved at low electrolyte flow rates and high cell currents are attribut ed 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.