Study on the Physico-chemical Properties and Microstructure of Lime Rapidly Calcined at High Temperature

It is a vital measure of energy-saving and emission reduction for iron and steel industry that limestone is used instead of active lime in converter steelmaking process. The effect of the microstructure on the reactivity and physico-chemical properties of lime were investigated. The limestone (12.5-15mm) was calcined fastly at 1450・C for 5min to 15min. The results show that the escape of CO2 promotes highly developed micropores forming after calcining at 1450・C for 5min to 10min. With the extension of calcining time, CaO recrystallizes and grows up, resulting in the disappearance of micro pores and densification for the structure of lime. With regard to the physic-chemical properties, the porosity of lime quickly increases at first and then decreases, which reaches the maximum at 10min, with the extension of calcining time. However, the variation of bulk density is opposite. The specific surface area of lime decreases with the extension of calcining time. The reactivity of lime reaches the maximum when calcined for 10min. In the condition of high temperature and fast calcination, CaCO3 decomposition is from the outside to the inside. CaO grain on the surface of lime has recrystallized, grown up and become dense, but CaCO3 is still in the decomposition inside of lime, leaving a lot of micro pores.