Understanding smective-water complex

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Smectite is a clay mineral able to adsorb water. Water is retained between smectite layers; forming a complex with the interlayer cations that balance the charge caused by is omorphous substitution within the layers. This ability to adsorb water is an important control of the physical and chemical properties of soils and surface sediments: stability, subsidence and rising, plant nutrient availability, mobility of chemical species, water availability, etc. Water adsorption on smectite is controlled by the degree of water saturation, the nature of the interlayer cation and the extent and distribution of the layer charge. The effect of layer extent and distribution is not sufficiently understood yet and it is the focus of this study.

The project has 3 goals:
1) Study th e effect of layer charge on smectite hydration. For this, 3 specimens with different charge and charge distribution will be studied by means of X-ray diffraction, thermo gravimetry, infrared spectroscopy and nuclear magnetic resonance to obtain the accurate description of layer charge distribution, layer hydration state and ofw ater coordination at the atomic scale.
2) Investigate smectite dehydration mechanism. This will be achieved by isothermal dehydration experiments at several temperatures, using X-ray diffraction, infrared and thermogravimetry.
3) Study dehydration during the first stages of the smectite illitization and discriminate between this process and simple dehydration. Smectite will be altered to ¡Hite at different extent, in hydrothermal experiments at several temperatures and for different times. The products will be analysed in similar ways as the specimens in goals 1and 2 to study how the illitization reaction affects the hydration state and to compare the parameters governing simple dehydration and dehydration caused by illitization.

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THE NATURAL HISTORY MUSEUM, LONDON

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