Hematite Dissociation Mechanism and Kinetics in Iron Ore Pellets during Heat Treatment

The mechanisms of magnetite oxidation (forward reaction) and hematite dissociation (reverse reaction) are considered in terms of a general kinetic approach. The dissociation in a pellet is found to develop during sintering when temperature increases. A derivatograph is used to perform experiments with Kachkanar fluxed pellets at various heating rates in a gas containing various oxygen contents. The reaction surface and the dissociation rate are found to increase with the temperature and the slag-forming oxide content. The heating of samples in a reducing atmosphere is studied. The temperature range of reduction of partially dissociated pellets, in which their intense destruction induced by the hematite–magnetite transition does not occur, has been determined. Based on the results of analyzing the pore structure of a pellet, we conclude that, when a melt appears in the system, the dissociation in a pellet is associated with both liquid-phase sintering, when closed porosity forms, and an increase in temperature. The results obtained in this work are of great practical importance, since the use of partially dissociated pellets excludes hematite reduction in them at low temperatures and does not lead to a violation of the gasdynamic conditions of blast-furnace melting.