Recovery of Zinc as Hydrated Zinc Sulfate salts from Zinc Dross

Zinc dross is a by-product of an industrial hot-dip galvanizing process, which could contain up to 95% Zn. Dross formation accounts approximately 15 % Zinc loss of the total Zinc usage. Therefore, reclamation of Zinc from bottom dross is of imperative concern. The present study explores the recovery of Zinc from Zinc dross through hydrometallurgical route. In particular, the study deals with the production of various grades of high purity hydrated Zinc sulfate salt from Zinc dross following leaching-purification-crystallization route. It was observed that through appropriate play of crystallization parameters mainly specific gravity (s.g.) and evaporation temperature (T) desired degree of hydration in Zinc sulfate can be achieved. Zinc dross (as such) was leached in sulphuric acid medium (~8.9% (v/v)) at ambient temperature for 24 h to get a 130 g/L Zn solution. Subsequently, iron removal was achieved by oxidation and precipitation using H2O2 and lime respectively. Further, the purified leach solution (pH~5) was taken for the crystallization of different hydrated Zinc sulfate salts. The optimum conditions for the crystallization of ZnSO4. H2O are s.g. (~1.9) and T (~70 oC) followed by the hot filtration, whereas for ZnSO4.7H2O, the conditions are s.g. (~1.9) and T (~80oC) followed by cold filtration at ambient temperature condition. However, ZnSO4 (anhydrous) are obtained at s.g. (~2.1) and T (~70 oC) followed by hot filtration. Thus, this study offers promising route for the production of different grades of high purity Zinc sulfate salts from Zinc dross.