Acid-leached mixed vermiculites obtained by treatment with nitric acid

• Published in: Applied clay science 2015-02, Vol.104, p.286-294
• Main Authors: Santos, S.S.G., Silva, H.R.M., de Souza, A.G., Alves, A.P.M., da Silva Filho, E.C., Fonseca, M.G.
• Format: Article
• Language: English
• Subjects: Acid leaching; Aluminum; Dissolution; Leached-clay mineral; Lixiviation; Magnesium; Nitric acid; Silicon dioxide; Specific surface; Vermiculite
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2014.12.008

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 4molL−1 HNO3 at 80°C for 4h 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. The reaction between the pristine vermiculite and acid nitric resulted in a discolored solid. [Display omitted] •Two vermiculites leached with HNO3 resulted in solids with high surface areas.•Acid-activation decreased the crystallinity of the vermiculites.•The layered structures of solids were maintained after lixiviation.•The dissolution rate decreased in the order Mg2+>Al3+>Fe3+ for both vermiculites.