THE EFFECT OF ADDITIVES ON ZINC DEPOSITED FROM ZINC-SULFATE SOLUTIONS

Zinc is industrially electrowon from acid zinc sulfate solutions at ambient temperatures. Some refining agents 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 (TAS) were used separately and in combination as grain refiners of the cathodic deposits. Current efficiency determination experiments were performed 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 TAS 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.