Thermal degradation kinetics and structural characterization of sodium bentonite

Abstract

ABSTRACT The thermal-decomposition behavior of a sodium-bentonite sample was investigated in this study. Non-isothermal pyrolysis tests were performed through simultaneous thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis to characterize the thermal-behavior of the bentonite sample in a temperature range from ambient to 750°C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) were used to determine the changes in mineralogy, structural features and morphology of bentonite before and after pyrolysis at 750°C. Iso-conversional methods were used to obtain kinetic-parameters such as the activation energies whereas Coats-Redfern (CR) method was used to find the most probable reaction mechanisms involved on the bentonite pyrolysis. XRD analysis showed that bentonite sample was mainly composed of sodium montmorillonite and a minority of other minerals such as quartz, plagioclase, alkali feldspar, cristobalite and calcite. Structural collapse of the clay mineral due to the thermal treatment was confirmed through XRD, FT-IR and SEM. Results indicated that thermal-decomposition of bentonite is carried out in two stages: a dehydration following a diffusion-controlled kinetics with an average activation energy of 72.23 kJ/mol, and a dehydroxylation characterized by a second-order kinetics with an average activation energy of 228.28 kJ/mol.