Hydrometallurgical Recovery of Zinc from Fine Blend of Galvanization Processes

Abstract

In many factories, which are working in the field of steel industry, there are galvanization units in which steel products are galvanized for corrosion protection. About 15% of the total amount of the used zinc are accumulated as zinc ash and dust at the surface of molten zinc bath and in the chimney respectively. In a previous work, zinc was successfully recovered from the coarse ash by applying pyrometallurgical processing. In this work, zinc fine blend (of fine ash and flue dust) was hydrometallurgically treated using sulfuric acid. Two alternative techniques were applied for producing zinc sulfate salt or pure zinc metal. In the first technique, the salt was separated from the leach solution as zinc sulfate hydrate (ZnSO₄ · H₂O). It was crystallized by concentrating the leach liquor to a density of 1.52 g/cm³. The purity of the produced zinc sulfate was 99.5%. In the second technique, the leach solution has been purified with respect to the soluble impurities using precipitation. The electrowinning technique was applied for producing a pure zinc metal from the purified solution. Electrolysis was performed at ambient temperature (25–28°C) with current density (c.d.) of 40 mA · cm⁻². The recovery of zinc proceeds down to a concentration of 50 g · l⁻¹ with acceptable cathodic current efficiency of 96.5%, and energy consumption for the electrolysis step of 2.75 KWh/Kg. The zinc purity in the deposit obtained from the electrolysis was 99.9%.

Keywords:

• Zinc recovery
• fine ash and dust
• leaching
• crystalization
• electrowinning

Acknowledgements

The authors gratefully appreciate Prof. S.E. Afifi and Prof. A.E. Saba, for their help and advice regarding this work.