Thermal analysis of a white calcium bentonite

Abstract

A white calcium bentonite (CaB) taken from ÇamlIdere (Ankara, Turkey) region was heated at various temperatures between 100 and 1100 °C for 2 h. The mineralogy of the CaB was determined as calcium smectite (CaS), metahalloysite (MH), opal-A (OA), opal-CT (OCT), quartz (Q), feldspar (F), and calcite (C) using the X-ray diffraction patterns of the natural CaB and its heated samples. Besides the XRD patterns, the thermogravimetry, differential thermal analysis, and low-temperature nitrogen adsorption (N 2 -AD) data show that the CaS lose adsorbed and hydration water up to 300 °C, dehydroxylation takes place between 300 and 750 °C, and then the 2:1 layer structure completely collapses above 900 °C. The activation energies for the dehydration and dehydroxylation were calculated as 7636 and 48838 J mol -1 , respectively, from the TG data using Coats and Redfern method. The specific surface area (S) and specific micro-mesopore volume (V) obtained from N 2 -AD data were 44 m 2 g -1 and 0.100 cm 3 g -1 for the natural CaB. S and V reach their maxima of 105 m 2 g -1 and 0.155 cm 3 g -1 , respectively, at 300 °C, remain approximately constant as the temperature increases up to 700 °C and then decrease almost in parallel with each other, reaching their minima at 900 °C. This indicates that the S and V values increase gradually during dehydration and dehydroxylation of the CaS. © 2010 Akadémiai Kiadó, Budapest, Hungary.