Effects of carbonaceous matter additives on kinetics, phase and structure evolution of coal-series kaolin during calcination

Abstract

Abstract In this study, the influence of carbonaceous matter on the kinetics, phase, and structure evolution of coal-series kaolin during the calcination process was systematically investigated. The pyrolysis characteristics were studied by thermogravimetric–differential-thermal-gravity–differential-scanning-calorimetry (TG–DTG–DSC), and the kinetic parameters were calculated by the Coats–Redfern (CR) method and the Flynn–Wall–Ozawa (FWO) method. Furthermore, the changes in the mineral composition, chemical structure, and morphology of the samples during calcination were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) analyses. The kinetic analysis demonstrates that the calcination reaction behaviors of the coal-series kaolin without and with carbonaceous matter additives were according to the third-order reaction model (F3); the differential expression of the F3 mechanism is g(α) = (1 − α)−2 – 1. The activation energy (Ea) and pre-exponential factor (lnA) increased by 7–14% and 13–23%, respectively, with carbon content addition increased from 2% to 6%. The relative decomposition rate of the kaolinite in the coal-series kaolin increased, the absorption peaks of the kaolinite decreased gradually, and the scale-shaped lamellar structures of the coal-series kaolin samples became irregular and amorphous with increasing carbon content under similar calcination conditions. Carbonaceous-matter additives can promote the thermal decomposition of coal-series kaolin during the calcination process.