Hydrothermal Reactivity of Mixed-Layer Kaolinite/Smectite: Experimental Transformation of High-Charge to Low-Charge Smectite

D. Proust1, J. Lechelle2, A. Lajudie2 and A. Meunier1
1 Laboratoire de Pétrologie des Alterérations Hydrothermales Université de Poitiers, 86022 Poitiers Cedex, France
2 Commissariat à l'Energie Atomique, DRDD/SESD 92260 Fontenay-aux-Roses, France

Abstract: A mixed-layer kaolinite/smectite (K/S) containing trace amounts of quartz, discrete kaolinite, goethite-hematite, and calcite was hydrothermally reacted with deionized water at 150°, 200°, and 250°C for 1 to 12 months. The starting K/S contained 50% smectite consisting of 15% low-charge and 35% high-charge layers. The X-ray powder diffraction and chemical analyses of the reacted products indicated a progressive reaction from high-charge to low-charge smectite as a function of time and temperature. The reaction reached completion after 4 months at 250°C, at which point high-charge smectite layers entirely reacted to low-charge smectite layers, the latter maintaining a constant proportion of about 90% for longer run durations. For long reaction times, discrete kaolinite totally reacted, whereas quartz showed only partial dissolution and iron oxides remained stable. Thus, the reaction of high-charge to low-charge smectite layers may be expressed as: high-charge smectite + kaolinite (both interstratified and discrete component) + quartz → low-charge smectite.

Key Words: Cation-exchange capacity • Hydrothermal transformation • Kaolinite/smectite • Layer charge • Smectite • X-ray powder diffraction

Clays and Clay Minerals; August 1990 v. 38; no. 4; p. 415-425; DOI: 10.1346/CCMN.1990.0380411
© 1990, The Clay Minerals Society
Clay Minerals Society (www.clays.org)