Effect of CO gas concentration on reduction rate of major mineral phase in sintered iron ore

As a fundamental study for clarifying the reduction phenomena of iron ore sinter in blast furnace, iron oxide (H) and quaternary calcium ferrite (Cf) were prepared and these kinetic behaviors at the final stage of reduction with CO-CO₂ gas mixture were studied. Reduction rate increased with increasing reduction temperature. Moreover, it increased with increasing partial pressure of CO gas. Difference of reduction rate caused by gas composition is much larger than reduction temperature. From comparisons of weight loss curves, reduction rate of H samples was faster than that of Cf samples under the same or similar conditions. Reduction reaction of H and Cf samples proceeded topochemically at higher temperature (≥1100°C), and didn't proceed topochemically at lower temperature (≤1 000°C). Besides, the reduction reaction of samples with CO rich gas proceeded more topochemically. Structure of iron layer in H samples was affected by temperature and gas composition. On the other hand, structure of iron layer in Cf samples was almost the same in all experimental conditions. Reduction data were analyzed based on one interface unreacted core model, and chemical reaction rate content k_c and effective diffusion coefficient in product layer D_e were determined. The values of k_c show Arrhenius-type temperature dependency, and were approximately same tendency except for Cf samples with near equilibriums gas compositions. The values of D_e of H samples show the temperature and gas composition dependencies, and that of Cf samples were approximately constant in all experimental conditions.