Study of iron ore pellets hardening mechanisms in the process of burning

Abstract

One of the important characteristics of burnt iron ore pellets, which largely determines their quality, is their strength properties. A review of scientific papers on the mechanism of pellets hardening during firing and the influence of various factors on their hardening presented. It was shown that the hardening of iron ore pellets occurs as a result of sintering of particles and the formation of a liquid phase. The sintering process, being a diffusive one, depends on time, and the formation of the liquid phase is determined by the composition of the charge. The results of the study of sintering and formation of the liquid phase in iron ore pellets under various technological factors presented, the study being performed at the Department of metallurgy and metal science of STI NRTU “MISiS” are presented. Conditions for the formation of the liquid phase during the hardening of pellets were studied using bentonite, limestone, dolomite and brucite as components of the charge. It was established that at using bentonite, the liquid phase is formed at a temperature of 1200°C. When using limestone to form the liquid phase, it was necessary to increase the firing temperature to 1250°C. With the addition of dolomite, the transition of the mixture to the liquid phase was achieved at a heating temperature of 1280°C. The brucite mixture with concentrate did not form the liquid phase even at a temperature of 1280°C. Studies of the influence of the exposure time of pellets in the high-temperature zone on the formation of their strength properties have shown that the dependence is an extreme one. Studies on a metallographic microscope determined the porosity of the obtained pellets in the center and in the surface zone. It was found that with increasing exposure time, the number of pores in the pellet both on the surface and in the center decreases. Due to the exit of the pores onto the surface, the pellets were compacted. The results of the presented studies can be used to change the quality characteristics of pellets by regulating the temperature and time regime of their firing.