A study of acidity and structure of hydroxy-Cr intercalated bentonites

Abstract

Hydroxychromium bentonites were prepared using hydroxychromium solutions with a OH/Cr content of about 1 and 2. The samples were heated in air and vacuum to study the influence of temperature and atmosphere on their final properties. Structural characteristics were obtained using X-ray diffraction and sorption of nitrogen. The surface chemistry was evaluated by means of infrared spectroscopy and potentiometric titration. The results obtained demonstrate the influence of the content of intercalating solutions on the properties of clays. Intercalation caused a fourfold increase in the surface area compared to the initial bentonite. Potentiometric titration and IR provides the evidence of innersphere complexation of the interlayer Cr with siloxane oxygen. The pK(a) distributions revealed peaks characteristic of chromium polymers (Cr(III)). Heat treatment of intercalated samples in air caused oxidation of Cr species resulting in Cr(VI).