Preparation and characterization of acid-activated bentonite powders

The Kütahya calcium bentonite (CaB) from Turkey shows significant changes in crystal structure, chemical composition and porosity with H2SO4 activation realized by heating its acidic aqueous suspension at 97 °C for 6 h. The acid content was changed from zero to 70% by mass, based on the dry bentonite–acid mixture. It was estimated from chemical analysis (CA) and X-ray diffraction (XRD) data that the CaB contains 65% calcium montmorillonite (CaM) and 30% opal-CT (OCT) by mass, and also illite (I) and other impurities in lower extents. The decrease in crystallinity of the CaM by the activation was discussed as regards to the decrease in the relative intensity (I / I0) and increase in the full width at half-maximum peak height (FWHM) of the 001 XRD peak for CaM with the H2SO4%. The CA data reveals that the relative content of the undissolved cations in the CaB increase in the order of Ca2+, Na+, Mg2+, Fe2+,3+, Al3+, K+, Si4+, and Ti4+ with H2SO4%. The specific micropore volume (Vmi) and specific mesopore volume (Vme) of the samples were estimated from N2-adsorption and desorption data, by standard methods. The Vme shows a ‘zig-zag’ increase from 0.104 cm3g− 1 to a maximum of 0.232 cm3g− 1 at 40% and then decrease to 0.149 cm3g− 1 at 70% H2SO4, respectively. The Vmi increases about from zero to 0.055 cm3g− 1 at 10% H2SO4 and then stayed approximately constant.