Thermal analysis of a white calcium bentonite

• Published in: Journal of thermal analysis and calorimetry Vol. 101; no. 3; pp. 873 - 879
• Main Authors: Bayram, Hale, Önal, Müşerref, Yılmaz, Hamza, Sarıkaya, Yüksel
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-09-2010; Springer
• Subjects: Adsorption; Analysis; Analytical Chemistry; Bentonite; Calcite crystals; Calcium; Calorimetry; Carbonates; Chemistry; Chemistry and Materials Science; Clay; Dehydration; Diffraction; Exact sciences and technology; General and physical chemistry; Hydration; Inorganic Chemistry; Ion-exchange; Maxima; Measurement Science and Instrumentation; Other ion exchangers: preparations and properties; Physical Chemistry; Polymer Sciences; Smectite; Specific surface; Surface physical chemistry; Thermal analysis; X-rays; Bentonite; Dehydroxylation; Pore volume; Dehydration; Surface area; Activation energy; Clay; Calcium Compounds; X ray diffraction; Pore size; Surface properties; Thermal analysis; Kinetic parameter; Porosity; Physicochemical properties
• ISSN: 1388-6150; 1588-2926; 1572-8943
• DOI: 10.1007/s10973-009-0626-y

A white calcium bentonite (CaB) taken from Çamlıdere (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.