ABSTRACT
The Chapter describes the quality parameters of pellets affecting the iron-making process and their dependence on the influencing variables. Their interrelationship with bonding in pellets and their textural characteristics are described. The influencing variables—process related, such as ore characteristics in terms of fineness and alumina content, addition of binder, pellet basicity, and MgO and FeO contents; and also those operation related, such as induration conditions (addition of carbon, bed height, feed rate, firing temperature, etc.)—are described in the text. The schematic of strength development in the pellets that undergo densification with the increase in firing temperature is also represented. The pellet porosity and its characteristics are important to the diffusion of reducing gases and affect its reducibility and reduction–degradation index (RDI). Their dependence on the pellet basicity and the contents of Al2O3 and MgO, when incorporated through lime and dolomite/pyroxenite, are outlined. The increase in melting point of the binding phases and their changes with MgO addition are explained. The formation of silicates and ferrite minerals and also micropores and macropores in the pellets and their effect on the reduction parameters, as their chemical constituents change, are mentioned in the text. The practice of MgO added fluxed pellets, having improved reduction behavior, are reported. The phenomenon of swelling during the reduction of the hematite phase to magnetite and its correlation with the formation of whiskers in pellets is described. The swelling mechanism in terms of stress development, dependence on gangue content in the concentrate, pellet basicity, and MgO content are described. The importance of lime assimilation in the pellets being indurated, and their role to control the firing temperature in induration to improve swelling is outlined.
