Sintering of Montomorillonites Pillared by Hydroxy-Aluminum Species

D. Tichit, F. Fajula, F. Figueras, B. Ducourant, G. Mascherpa, C. Gueguen and J. Bousquet
Laboratoire de Chimie Organique Physique et Cinétique Chimique Appliquées, UA 418 CNRS, ENSCM 8, rue Ecole Normale, 34075 Montpellier Cedex, France
Laboratoire des Acides Minéraux, USTL-UA 79 Place Eugène Bataillon, 34060 Montpellier Cedex, France
Centre de Recherches ELF-Solaize Saint Symphorien d'Ozon, France

Abstract: The sintering of montmorillonites pillared by hydroxy-Al species was investigated by several techniques. The change of the microporosity of the pillared interlayer clay with temperature shows that sintering was mainly due to the loss of microporosity. On calcination of the parent clay at 760°C the X-ray powder diffraction pattern did not change; the 060 line shifted only slightly from 8.988 to 9.017 Å. The infrared (IR) spectrum suggested some dehydroxylation, but the structure appears to have been preserved. On calcination of the pillared clay at >700°C, the intensity of the 001 line decreased steadily, the 060 line broadened, and the b parameter decreased slightly from 8.988 to 8.928 Å. Fe3+ ions apparently occupied only one site after calcination at 300°C and two sites after calcination at 700°C. Smaller isomer shifts and higher quadrupole splittings in the Mössbauer spectra suggest that calcination produced more covalent bonding of Fe3+ and a highly distorted structure. The IR spectrum was significantly modified by calcination of the sample, and the 935- and 1125-cm−1 bands disappeared and the 1035-cm−1 band broadened. These results suggest that at <700°C the pillars sintered and that the clay progressively decomposed at >750°C. The pillaring-induced decrease of thermal stability of the clay was likely due to the introduction of protons during the first step of the preparation. The thermal stability of these Al-pillared interlayer complexes is comparable to that reported for hydroxy-silicoaluminum montmorillonites and fluorhectorites.

Key Words: Calcination • Hydroxy-Al • Infrared spectroscopy • Montmorillonite • Mössbauer spectroscopy • Pillared interlayer complex • Thermal stability

Clays and Clay Minerals; August 1988 v. 36; no. 4; p. 369-375; DOI: 10.1346/CCMN.1988.0360413
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)