摘要
The carbon gasification has a great effect on reduction behavior of iron ore pellets containing carbon, especially in neutral atmosphere. General speaking, adding any additives, which can promote carbon gasification reaction, can enhance the reduction rate of iron ore pellets containing carbon in neutral atmosphere. Investigations［1-4］ showed that alkali-metal compounds have obviously catalysis effect on the carbon gasification reaction, but the mechanism is understood insufficiently. As the vaporization temperatures of these alkali-metals are lower than 1 373 K, such as the vaporization temperature of sodium and potassium is 1 153 K and 953 K［5］ respectively, at this temperature iron ore pellets may be reduced at a higher reduction rate, and alkali-metals may be vaporized in the catalytic process of composite pellets by different mechanisms. Those vaporized alkali metals may react with iron ore pellets containing carbon in pre-reduction furnace, such as shaft furnace to generate cyanides, fluorides, silicates, carbonates and oxides. As those generated matters can deposit on the surface gaps both on pellets and furnace refractory lining, and then affect adversely the strength pellets and destroy furnace refractory lining. From the viewpoint of metallurgical industry, adding some alkali-metal compounds to enhance reduction rate of composite pellets［6-9］ is challenging.
The effect of some metallurgical fluxes, such as CaO, CaCO3, on reduction rate of composite pellets has not been reported extensively［10-12］. This paper is to present the effect of CaO and CaCO3 on reduction rate of iron ore pellets in nitrogen atmosphere.
The effect of metallurgical fluxes CaO and CaCO3 on the reduction rate of iron ore pellets containing carbon in nitrogen atmosphere has been studied by a weight-loss thermal balance. The experimental results showed that adding CaO or CaCO3 can promote reduction reaction as the added CaO or CaCO3 probably decrease the apparent activation energy of iron ore concentrate-carbon-CaO or CaCO3 reaction, and the reduction rate constant changes with mass percent of CaO and CaCO3. The kinetic analysis also showed that the rate-controlling step of the reaction is inner gas diffusion.
