Oxidation of iron ore at moderate and high temperatures

Abstract

The oxidation of magnetite and titanomagnetites in iron-ore sinter at moderate (400–1000°C) and high (1000–1350°C) temperatures is subjected to physicochemical analysis. The oxidation kinetics is studied on briquets of Olkhovsk magnetite concentrate and Kachkanar titanomagnetite concentrate, as well as samples of unfluxed Kachkanar pellets and pellets fluxed to a basicity of 1.3. At moderate temperatures, the limiting stage in oxidation is the diffusion of the reagent to sections of the surface smaller than the total spherical surface. At high temperatures, in both isothermal and nonisothermal conditions, the limiting stage in oxidation is the diffusion of oxygen in pellet pores. From the kinetic equations for isothermal oxidation, the apparent activation energy with the specified degree of conversion is calculated; its variation is associated with change in the type of reagent diffusion through the layer of reduction products. The apparent diffusion coefficients of oxygen in Kachkanar pellets are determined at 500–1000°C. A method has been developed for determining the degree of pellet oxidation as a function of the time and the temperature in nonisothermal conditions. This method may be used to calculate the oxidation of the pellets in roasting on conveyer machines. The results may be used to determine the degree of oxidation in the roasted pellet bed and to optimize the heat-treatment parameters in roasting systems.