Study on Lime Activity of Limestones with Different Properties after High Temperature Calcining

　　Lime is one of the most important slag-making materials for converter steelmaking. The ability of lime to participate in the slag-making reaction in the steelmaking process is usually expressed by the "activity" of lime. Generally, the activity measured by acid-base titration is 300mL ( Lime above 4N-HCl) is called active lime. At present, the active lime used in converter steelmaking is mainly made by fully preheating limestone at 700～900℃ in rotary kiln or shaft kiln, and then calcining it at 1050～1200℃. The lime is cooled to room temperature and sent to steelmaking plant for slagging. material. This process on the one hand loses the physical heat of the high-temperature lime, on the other hand the coal gas consumed by the calcined lime emits the greenhouse gas CO2.

　　 Scholars from Wuhan University of Science and Technology have studied the relationship between the activity of lime and the physical and chemical properties of limestone raw materials when limestones with different properties are quickly calcined at a temperature much higher than the optimum calcination temperature for active lime. The activity of lime was measured by hydrochloric acid titration, the phase composition of limestone and lime was measured by XRD, the morphology of CaCO3 in limestone and the microstructure change of CaO grain in lime were observed under scanning electron microscope. The test results show that the smaller the grain size of CaCO3 in limestone, the lighter the degree of sintering and densification of CaO grains in the lime obtained by high-temperature rapid calcination, and the higher the activity of lime; when the high-temperature calcination time is extended to 15min at 1450℃, the difference is different The CaO grains in the lime calcined from limestone with CaCO3 grain size have all been fused and grown, and the activity has been significantly reduced; the SiO2 in the limestone has a great influence on the activity of the calcined product. When the content of SiO2 is high, the lime will be quickly calcined at high temperature. The degree of activity is significantly reduced. Therefore, the smaller the grain size of CaCO3 and the lower the content of SiO2 in limestone, the more favorable it is to obtain lime with high activity under high temperature and rapid calcination conditions.