Acid-leached mixed vermiculites obtained by treatment with nitric acid

Two samples of pristine vermiculites (V and V*) were reacted with nitric acid under controlled conditions. Structural and textural studies were performed using chemical composition, X-ray diffraction (XRD), 29Si and 27Al NMR, adsorption/desorption gaseous nitrogen measurements, SEM and TEM. Acid-activation increased the specific surface area and porosity of the samples and led to partial leaching of iron, aluminum and magnesium from the octahedral sheets. Acid leaching of the two vermiculite samples with 3 and 4 mol L− 1 HNO3 at 80 °C for 4 h nearly removed all the MgO, Al2O3 and Fe2O3, and left behind SiO2-containing residue. The elements were easily extracted from both samples and the dissolution rate decreased in the order Mg2 + > Al3 + > Fe3 +. XRD showed the formation of products with low crystallinity for both vermiculites treated with high acid concentrations.