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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~ Some remarkably high values of current efficiency were observed especially at 75~ 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~ was 1.253 kWh/kg. In the presence of 0.37 rag/1 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/cm 2. * Electrochemical Society Student Member.

Zinc is industrially electrowon from acid zinc sulfate solutions at ambient temperatures. Some refiningagents are usually added to improve the deposit qualities. Gelatin is a traditional additive, but other additives are also used. In the investigation described here, the basic parameters of deposition (e.g., current density, acid concentration, and zinc concentration) were optimized. Gelatin and a tetraalkylammonium salt (T AS) were used separately and in combination as grain refiners of the cathodic deposits. Current efficiency determination experiments were perf.ormed to investigate the role of these additives. Scanning electron micrographs of the cathodic deposits were obtained to examine the surface qualities of deposits at certain conditions. Results showed that gelatin is generally a better refiner,although T AS may be used in concentrations of 0.074 mg/l to 1 mg/l. A mixture of the two additives resulted in a decrease of current efficiency. 100

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