Kinetics of thermal decomposition of hydrated minerals associated with hematite ore in a fluidized bed reactor

Abstract

The kinetics of removal of loss on ignition (LOI) by thermal decomposition of hydrated minerals present in natural iron ores (i.e., kaolinite, gibbsite, and goethite) was investigated in a laboratory-scale vertical fluidized bed reactor (FBR) using isothermal methods of kinetic analysis. Experiments in the FBR in batch processes were carried out at different temperatures (300 to 1200A degrees C) and residence time (1 to 30 min) for four different iron ore samples with various LOIs (2.34wt% to 9.83wt%). The operating velocity was maintained in the range from 1.2 to 1.4 times the minimum fluidization velocity (U (mf)). We observed that, below a certain critical temperature, the FBR did not effectively reduce the LOI to a desired level even with increased residence time. The results of this study indicate that the LOI level could be reduced by 90% within 1 min of residence time at 1100A degrees C. The kinetics for low-LOI samples (< 6wt%) indicates two different reaction mechanisms in two temperature regimes. At lower temperatures (300 to 700A degrees C), the kinetics is characterized by a lower activation energy (diffusion-controlled physical moisture removal), followed by a higher activation energy (chemically controlled removal of LOI). In the case of high-LOI samples, three different kinetics mechanisms prevail at different temperature regimes. At temperature up to 450A degrees C, diffusion kinetics prevails (removal of physical moisture); at temperature from 450 to 650A degrees C, chemical kinetics dominates during removal of matrix moisture. At temperatures greater than 650A degrees C, nucleation and growth begins to influence the rate of removal of LOI.