analysis of carbothermic restoration of zinc ferrite

Abstract

Remelting scrap steel, including galvanized steel, in arc steel furnaces is accompanied by the formation of dust. Carbothermic reduction of dust in Waelz kilns at heating temperature up to 1200 °С is the main method of dust processing. The target products of the process are zinc oxide, which is formed as a result of the oxidation of reduced zinc vapor in the gas exhaust tract, and reduced iron in the composition of solid cinder. The work carried out a thermo-dynamic analysis of transformations during the carbothermic reduction of zinc ferrite ZnFe2O4, which is the main com-ponent of dust. In the first version, the carbothermic reduction of zinc ferrite with a stoichiometric amount of carbon at the temperature is increased to 1200 °C simulates a hypothetical situation when all components of the charge are crushed to an ultrafine state. In this case, there are no kinetic difficulties in delivering the reducing agent to the reduced oxides. In the second version, zinc ferrite is reduced with an increasing amount of carbon at a temperature of 1200 °С. This option simulates the process of dosed delivery of carbon to the surface of a solid oxide particle, which is typical for most heterogeneous reactions. According to the results of the first calculation option, iron is first reduced from oxides to form iron carbide Fe3C. Then zinc oxide is reduced in the temperature range 800–940 °С, and the main reducing agent is carbon of iron carbide. In the second version of the calculations, the sequence of transformations is radically different from the first option. Zinc oxide is reduced first, with only 36% of the total carbon consumed. The remaining carbon is spent on the reduction of iron oxide; the product of reduction is metallic iron. Thus, in real conditions, obtaining low-carbon iron in cinder is quite possible if the appropriate technological conditions are observed