Relationship between Textural Parameters of Lamellar Products Obtained by Acid Activation of Pure and Commercial Vermiculites and Their Iron and Water Content

Abstract

The relationship between textural parameters (specific superficial area (SBET) and porosity (Vp)) of lamellar products obtained from HNO3-activated vermiculites and their iron and water content has been established. Two commercial vermiculites, one thermoexfoliated commercial vermiculite, and one pure vermiculite were nitric-acid-treated at 4 and 8 M concentrations for 1, 3, and 7 days. Untreated and treated samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and N2 physisorption analysis. The untreated vermiculites showed a direct relationship between their iron content and the values of SBET, Vp, and pore size; an inverse relationship was observed in the case of the treated samples. The iron content may prevent further leaching of cations but not water loss, therefore forming lamellar products with lower SBET and Vp values. The SBET and Vp values of the studied thermoexfoliated sample were higher than those of the starting sample. The SBET and Vp values of the activated thermoexfoliated sample were lower than those of the activated non-thermoexfoliated sample.