Influence of interlayer cations on the water sorption and swelling-shrinkage of MX80 bentonite

The potential of water sorption and swelling-shrinkage in the expansive clays is practically defined by the nature of interlayer cations. The purpose of this paper is to estimate the effects of the cation saturation (Mg+, Ca+, Li+, Na+, and K+) on the swelling-shrinkage behaviour of the MX80 bentonite. The MX80 bentonite (a commercial clay) was treated with concentrated solutions (1 N) of sodium, calcium, magnesium, potassium, and lithium chlorides. This treatment was made three times with constant agitation for 1 h. Then, the clay was washed three times with distilled water. The scanning transmission electron microscopy (STEM) and inductively coupled plasma atomic emission microscopy (ICP-AES) analyses were used to verify the efficiency of the cation saturation. Finally, two techniques were employed to estimate the effect of the cation saturation on the swelling-shrinkage behaviour of the bentonite: the first one uses an isothermal system of water adsorption, where the water activity is controlled by a supersaturated salt solution. In the second, environmental scanning electron microscopy (ESEM), coupled with a digital image analysis (DIA) program, was used to estimate the swelling-shrinkage potential at different water activities. The swelling-shrinkage isotherms were always estimated on isolated aggregates. The isotherms of water adsorption and swelling-shrinkage of the bentonite MX80 show that the amount of adsorbed water and the swelling-shrinkage potential depend directly on the interlayer cation. For example, the sodium bentonite presents an excellent capacity to swell while the lithium bentonite does not swell significantly at the aggregate scale. In addition, other textural properties may be modified by the cation saturation, such as the specific surface, the particle size, porosity, etc. (C) 2003 Elsevier B.V. All rights reserved.