Atmospheric leaching of steel-making wastes and the precipitation of goethite from the ferric sulphate solution

The hydrometallurgical processing of EAF dust and steel-making sludge with sulphuric acid was investigated at atmospheric pressure. The influence of acid concentration, temperature, time, and liquid/solid ratio was studied. Zinc extraction reaches almost 100% and iron extraction exceeds 90% in 3 M H2SO4 at 80 °C and L/S ratio of 5 after 6 h. A good selectivity with regard to zinc altogether with the relatively high zinc extraction was achieved in 0.1–0.3 M H2SO4 at 80 °C. In that range the zinc extraction was about 30% and the Zn/Fe ratio was about 9. The leach liquor was treated using goethite precipitation. The process was modified in order to minimize the consumption of the alkali and to reduce the sulphur and zinc content in the precipitate.