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

The relationship between textural parameters (specific superficial area (S_BET) and porosity (V_p)) 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 S_BET, V_p, 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 S_BET and V_p values. The S_BET and V_p values of the studied thermoexfoliated sample were higher than those of the starting sample. The S_BET and V_p values of the activated thermoexfoliated sample were lower than those of the activated non-thermoexfoliated sample.