Kinetic analysis of dehydroxylation of Ethiopian kaolinite during calcination.

The calcination process is the dehydroxylation reaction of the kaolinite mineral into the formation of amorphous metakaolinite phase. The dehydroxylation reaction of kaolinite is affected by various parameters such as calcination temperature, time and particles size. The present work aimed to analyze the kinetics of dehydroxylation reaction of Ethiopian kaolinite during calcination. The effects of temperature (550–675 °C), time (30–210 min) and particles size (0.900–0.106 mm) on the degree of conversion were also investigated. Subsequent to sample preparation and calcination, it was characterized by various analytical techniques such as X-ray diffractometer (XRD), Fourier transformer infrared spectrometer (FTIR), differential scanning calorimeter (DSC), thermogravimetry analyzer (TGA) and scanning electron microscope (SEM). The broadening of the XRD peaks was due combined effects of micro-strain and crystalline size. The crystalline peaks in the XRD curve and the hydroxyl bands in FTIR curve were disappeared in calcined kaolinite which revealed the formation of metakaolinite. In the TGA curve, three endothermic peaks and one exothermic peak were detected from 25 to 1100 °C. The conversion degree increased as calcination temperature and time were increased, and the particles size was reduced. The maximum conversion degree was 0.989 at 625 °C, 0.106 mm and 150 min. The dehydroxylation reaction results were well fitted with pseudo-first-order reaction rate kinetics. For the particles size of 0.900, 0.500, 0.250 and 0.106 mm, the activation energies were 263.105 ± 2.631, 252.831 ± 2.528, 250.727 ± 2.507 and 237.619 ± 2.376 kJ mol−1, respectively, for the pseudo-first-order rate kinetics. [ABSTRACT FROM AUTHOR]