Zn-recovery from steel making dusts - Kinetics and mechanism of thermal zinc-ferrite phase decomposition

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Zinc-iron concentrate as a by-product from EAF-dust processing (as well as from primary ore processing) counts as waste for disposal, although an available content of zinc represents about from 300 to 500 €/t. Every year approx. 65.000-75.000 tons zinc are lost in European countries. In former times this material was consumed in West-European Imperial Smelting Furnaces, but this technology now it is not accessible anymore after closure of those plants. Because of the presence of Cd, Zn and As in such materials their recycling disposal is not acceptable. At the moment the yield of metals by existing metallurgical treatment processes amounts smaller than 20 %. The high content of sulphur (5-13 mass percent) does not allow a treatment in the common Waelz process. This project focuses on a pyrometallurgical treatment of iron-zinc concentrate in order to study the mechanism and kinetics of thermal zinc ferrite phase decomposition. Fundamental experiments in a modified Tamman furnace should be performed in a very weak reducing atmosphere at 1150°C to prevent Zinc-gas-formation. After established optimal parameters the thermal decomposition of zinc ferrite will be investigated in a rotary kiln furnace in order to investigate the technical feasibility. The chemical equilibrium and the kinetics of this process step as well as for the subsequent hydrometallurgical recovery of zinc from a solid residue is studied with suitable computer models and validated under laboratory conditions. The research will be conducted as a DFG-partner project with the Institute of Chemical Technology in Prague.