Kinetics study on removal of LOI by thermal decomposition of hydrated minerals associated in hematite ore

Abstract

In the present study, the kinetics of removal of loss on ignition (LOI) by thermal decomposition of hydrated minerals associated with natural hematite iron ore 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 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 degrees C) and residence time (30, 45, 60 and 75 min) for iron ore sample. It is observed that beyond a certain bed depth (16 mm), 100 % removal of LOI is not found to be 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 'alpha' versus time and used for developing various forms of 'alpha' functions. The study demonstrates that decomposition of hydrated minerals associated with hematite ore is controlled either by chemical kinetics or nucleation or both. The estimated apparent activation energy values in all the experimental situations are found to be of the order of 70 kJ mol(-1), reinstating that the reactions are indeed controlled by chemical kinetics.