Why Organic Additives is Added to the Zinc Electrowinning Process?

Why Organic Additives is Added to the Zinc Electrowinning Process?

Organic additives are used extensively in zinc electrowinning to assist in controlling the process. The most common organic additive in Zn electrowinning is glue. The addition of animal glue to the zinc electrolyte used in zinc electrowinning plants seves several purposes.The glue additives control cathode growth to give smooth cathode zinc deposits, inhibit the deleterious effects that impurities such as antimony have on the current efficiency of zinc electrodeposition, and decrease acid mist evolution by formingstable foam layers on the electrolytic cell tops in conjunction with additives such as m-pcresol.

The addition of sodium lauryl sulfate to the zinc sulfate solution increased current efficiency, reduced power consumption and improved the surface morphology. Maximum current efficiency and minimum power consumption were achieved on addition of 0.02mg dm-3 Sb with 1mg dm-3 sodium lauryl sulfate. SLS and glue affected the cathodic polarization of zinc similarly and SLS is more effective than glue in counteracting the deleterious effects of Sb on electrowinning of zinc from acidic sulfate solution.

Increasing concentrations of thiourea in the electrolyte decreased the CE for zinc deposition; the additional presence of antimony did not significantly alter the decrease in CE but the presence of glue resulted in a further substantial decrease in CE. Thiourea changed the zinc deposit morphology and orientation, and also altered the shape of the zinc deposition cyclic voltammogram.