Extraction of zinc from zinc ferrites by fusion with caustic soda

Zinc ferrites are one of the major forms of zinc in some wastes, such as steel mill EAF dusts and the leaching residues of roasted zinc sulfide concentrates. These ferrites can be very difficult to chemically decompose so that the zinc can be recovered. This decomposition is the key to the recovery of zinc in these solid wastes. In this work, the recovery of zinc from synthetic zinc ferrite was investigated. It was found that around 75–80% of the zinc in zinc ferrite can be extracted after being fused directly with NaOH pellets and dissolved in an alkaline leaching solution. The recovery increased to over 90% when the ferrite was hydrolyzed with water or dilute NaOH solution prior to the fusion step.