Effects of firing temperaturc (1100°1300°C), slag content (5, 10 wt%), basicity [(wt%CaO)/(wt%SiO₂)=02], total porosity (0.050.45), and reduction temperature(800°1000°C)upon the reduction rate of hematite pellets are examined. Their pore-radius distributions, swelling, and microstructures in the course of reduction vary with the above-mentioned factors.
Swelling and pore-radius distribution of unreduced pellets influence the reduction rate in the early stage; the pellets of basicity 0.52 indurated at 1 250°C and pure hematite pellets of total porosity 516% indurated at 1 300°C have many closed-pores and/or small pores below 0.2 μ and show poor reducibility. The other pellets have many large open-pores and their reducibilities become better as total porosity and swelling increase.
In the later stage, the reduction rate varies according to the amount and diameter of wüstite particles encircled with dense iron (particle E) ; the reduction of basic pellets at 1 000°C is retarded remarkably in this stage, because the diameter of particle E is large (10 μ). As the diameter of particle E decreases, the reduction rate increases. Pellets having almost no particle E (e. g. the pellets of basicity 0.5) show good reducibility.
The pellets of basicity 01 indurated at 1 150°C have the best reducibility at the final stage.