Acidic leaching both of zinc and iron from basic oxygen furnace sludge

► The amount of leached zinc was the highest (70%) using 1 M concentration of sulphuric acid with the leaching time up to 15 min and at temperature of 80 °C. ► Choosing the right leaching conditions it is possible to leach zinc into the solution. ► By suitable adjusting of pH value it is possible to remove iron from the solution. ► Selected leaching conditions are valid only for the particular BOF sludge because the chemical and mineralogical composition of each steelmaking dust is individual. During the steel production in the basic oxygen furnace (BOF), approximately 7–15 kg of dust per tonne of produced steel is generated. This dust contains approximately 1.4–3.2% Zn and 54–70% Fe. Regarding the zinc content, the BOF dust is considered to be highly problematic, and therefore new technological processes for recycling dusts and sludge from metallurgical production are still searched for. In this study the hydrometallurgical processing of BOF sludge in the sulphuric acid solutions under atmospheric pressure and temperatures up to 100 °C is investigated on laboratory scale. The influence of sulphuric acid concentration, temperature, time and liquid to solid ratio (L:S) on the leaching process was studied. The main aim of this study was to determine optimal conditions when the maximum amount of zinc passes into the solution whilst iron remains in a solid residue.