Abstract
The cathode current efficiency for the electrowinning of zinc was determined under different conditions of alkali concentration (2–8M), current density (10–40 mA · cm−2), and temperature (30–75°C). Some remarkably high values of current efficiency were observed especially at 75°C. A possible mechanism involving the discharge of monovalent complex ions is suggested. The effect of two tetra‐alkyl ammonium salts TAS(a) and TAS(b) was investigated. The tetra‐alkyl ammonium hydroxide, TAS(a) was found more suitable than the tetra‐alkyl ammonium ethoxide, TAS (b). The morphology of zinc deposits was inspected by the scanning electronmicroscope; these were mainly spongy deposits. The cell voltage was measured and the energy consumption was calculated and was found to decrease with the increase of temperature. The total energy kWh/kg of deposited zinc from an additive‐free solution at 75°C was 1.253 kWh/kg. In the presence of 0.37 mg/l TAS(a), a further reduction was observed. The energy consumption amounted to 1.180 kWh/kg at the same temperature. The current density for maximum efficiency was 20 mA/cm2.
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