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1 Departamento de Química Agrícola, Geologíay Geoquímica, Facultad de Ciencias, Universidad Autónoma de Madrid, Campus Cantoblanco, E-28049Madrid, Spain, and 2 Laboratoire "HydrASA", UMR-CNRS 6532, Faculté des Sciences, F-86022 Poitiers, France
* E-mail: dominique.righi{at}hydrasa.univ-poitiers.fr
(Received 12 January 2004; revised 16 June 2004)
Hydrolytic exchange was performed experimentally on four smectitic clays to evaluate the extent of clay alteration induced by this process and the associated auto-transformation of H+ clays. Clay samples were Na-saturated and submitted to 10, 50 and 100 wetting-drying (WD) cycles and characterized after treatment using X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity analysis. Evidence for hydrolytic exchange was given by increasing amounts of exchangeable Mg2+ and precipitation of Na soluble salts for samples subjected to 100 WD cycles. Results indicated a decrease in the interlayer charge after 10 WD cycles but no further decrease was observed after 50 and 100 WD cycles. For one sample, XRD data indicated a decrease in the proportion of the smectite phase and a relative increase in the concentration of illite-smectite mixed layers also present in the sample. The results suggested that the reaction induces first a decrease in the layer charge and then a partial dissolution of some smectite layers.
KEYWORDS: hydrolytic exchange, smectite, auto-transformation, H+ clays, layer charge, XRD
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