Kinetics of reduction step of wustite to iron in gaseous reduction of quaternary calcium ferrite

As a fundamental study for clarifying the reduction phenomena of sintered ore in a blast furnace, quaternary calcium ferrite was synthesized from chemical reagents of Fe₂O₃, CaCO₃, SiO₂, and Al₂O₃ and the kinetic behavior at the final stage of reduction of the quaternary calcium ferrite with CO and H₂ gas was studied. The results obtained are summarized as follows: (1) Reduction rate increased with an increase in temperature both in CO and H₂ reductions. The increase of reduction rate with temperature was not very large above 900°C but it was remarkably large between 800°C and 900°C. (2) Reduction at 900°C and above proceeded topochemically both in macro- and microstructures. At 800°C, the reduction did not proceed topochemically but rather homogeneously. (3) Reduction data at 900°C and above were analyzed based on the unreacted-core model. Reduction curves calculated by using the rate parameters obtained by the analysis agreed with the observed data very well. Temperature dependencies of the chemical reaction rate constant ke and the effective diffusivity in the product layer De were given by following equations: ke_CO = exp (13.28-164.9 × 10³/RT) (m/s) (1173 approximately 1273 K) De_CO = exp (-7.16-32.07 × 10³/RT) (m²/s) (1173-1273 K) ke_H(2) = exp (3.62-55.83 × 10³/RT) (m/s) (1173 approximately 1273 K) De_H(2) = exp (-3.61-53.91 × 10³/RT) (m²/s) (1173 approximately 1273 K).