Study on kinetics of thermal decomposition of low LOI goethetic hematite iron ore

In the present study, the kinetics of thermal decomposition of hydrated minerals associated in natural hematite iron ores has been investigated in a fixed bed system using isothermal methods of kinetic analysis. Hydrated minerals in these hematite iron ores are kaolinite, gibbsite and goethite, which contribute to the loss on ignition (LOI) during thermal decomposition. Experiments in fixed bed have been carried out at variable bed depth (16, 32, 48 and 64 mm), temperature (400-1200 °C) and residence time (30, 45, 60 and 75 min) for iron ore samples. It is observed that beyond a certain critical bed depth (16 mm), 100% removal of LOI is not found possible even at higher temperature and higher residence time. Most of the solid-state reactions of isothermal kinetic analysis have been used to analyze the reaction mechanism. The raw data are modified to yield fraction reacted “α” versus time and used for developing various forms of “α” functions. f(α) is the inverse of first derivative of g(α) with respect to α. The study demonstrates that decomposition of hydrated mineral in hematite follows the chemical kinetics. The estimated activation energy values in all the experimental situations are found to high, of the order of 60 kJ/mol, reinstating that the reactions are indeed controlled by moving phase boundary and random nucleation.