Hydrometallurgical process development for the production of a zinc sulphate liquor suitable for electrowinning

This study deals with the development of an innovative hydrometallurgical process for zinc recovery from Waelz Oxide, a concentrate of zinc and lead oxides obtained pyrometallurgically from the treatment of EAF dusts.Its main objective is the production of a zinc sulphate liquor to be used as feedstock in electrolytic processes. The process requires different stages to achieve this goal. The first stage consists of a double-sulphuric-acid-leaching, achieving a 88% lixiviation of the zinc present in the Waelz Oxide. After the leaching, to fulfil the strict requirements of an electrolysis feed, some purifying stages, such as oxidation, removing more than the 99% of the iron present in the leach liquor, and cementation to remove cadmium, lead and copper were investigated. Finally, if the concentration of some metallic impurity is above the accepted level for electrolytic processes, an additional purification stage could be considered.Through this process, sulphate zinc liquors with a zinc purity of around 99.75%, containing less than 135 ppm of metallic impurities, could be obtained.