Temperature gradient during the reduction of self-reducing chromite pellets

The reaction rate of self-reducing agglomerates is very dependent on temperature and how fast is the evolution of temperature from the periphery to the center of the agglomerate. The temperature gradient is dependent on the heat flow from the surface to inner part which is affected by many factors like components and phases, particle size, porosity, chemical reactions, counter-flow of generated gases, etc. This gradient is higher: i) at the beginning of heating; ii) at high temperatures; iii) for highly endothermic reactions, such as for chromite carbothermic reduction reaction; iv) for large agglomerates. Self-reducing pellets of Brazilian chromite, containing petroleum coke, were agglomerated with Portland cement. These pellets were heated to 1,773 K (1,500°C) to analyze the reduction progress at the core and the external layers of the pellets. The products were analyzed by scanning electron microscopy (SEM) and EDS. There were morphological differences between the surface and the center of the self-reducing pellets, showing that the average intensity of the reaction depends on how fast the temperature rises in the core of the pellet. This heat flux improves with shrinkage of reduced pellets, the porosity reduction and with the formation of liquid phase (slag).