Selective leaching of zinc from zinc ferrite with hydrochloric acid

Zinc ferrite is a major constituent of the steel-making dust and sludge. In the present work the hydrometallurgical extraction of zinc from this material was studied. ZnFe2O4 and the sludge were leached in hydrochloric acid at atmospheric and elevated pressure using the microwave heating. More than 90% of zinc can be extracted with diluted acid when the temperature is 250 °C retaining iron in the new oxide matrix. The product resulting from the synthetic zinc ferrite contained 91% of hematite and 9% of zinc ferrite. Dried sludge from an oxygen open hearth furnace was converted into hematite containing 0.18% of zinc and 0.05% of lead. This material can be directly recycled or used as a pigment. Over 99% of the zinc was extracted from the sludge with 0.3 M HCl solution but the amount of iron in the solution was higher than for the pure ferrite treatment because the sludge contained also some magnetite and wustite.