Absorptive and Swelling Properties of Clay-Water System

Abstract

The subject of the adsorption and swelling properties of the clay-water system may be divided into three parts: (1) clay-water vapor system, (2) clay-liquid water system in the gel state, and (3) clay-liquid water system in the fluid state, i.e. pastes and sols. In studying the swelling of clays in relation to hydration, it is necessary to distinguish between the two kinds of swelling encountered; namely, the intramieellar swelling which involves the expansion of the crystal lattice itself, commonly known as the interlayer or interlamellar expansion, as found in montmorillonite, vermieulite-like, and in some of the hydrous mica clay minerals; and intermicellar swelling which involves an increase in volume due to adsorption of water molecules between individual clay particles. Intramieellar swelling can be identified and measured only by x-ray analysis, whereas the intermicellar swelling can be determined from a measurement of the total increase in volume of the clay body or of the clay-bearing material with apparatus designed for this purpose (Freundlich et al. 1932; Keen and Raczkowski 1921; von Bnsline 1933; Winterkorn and Baver 1934). The common feature among the clay minerals is their platy surfaces which consist either of oxygen ions organized into an hexagonal network, or of hydroxyl ions organized into a closely packed network. The oxygen surfaces characterize the montmorillonitic and the micaceous clay minerals, whereas both oxygen and hydroxyl surfaces characterize the kaolinitic and the chloritic clay minerals. One of the fundamental differences among the clay minerals lies in the amount and kind of exchangeable cations present on their surfaces, and in the seat of the excess negative charge of the crystal lattice which these cations neutralize (Hendricks 1945; Eoss and Hendricks 1945). The scarcity of the exchangeable cations relative to the number of the surface oxygen ions which bear the negative charge (the ratio of the oxygen ions to the cations may range from 3 to 1, as in the micas, to 18 to 1, as in some of the montmorillonites) has been advanced as the possible cause for the polarization of these surfaces and consequently for their reactivity with polar molecules (Barshad 1952). One of the important features, insofar as water adsorption is concerned, by which the various clay minerals may be differentiated, is the extent of the absorbing surface. Table 1 is a summary of the extent of the external surfaces of several of the clay minerals as measured by Na and ethane gas adsorption, and of the extent of the internal surfaces of montmorillonite as measured by glycol adsorption (Dyal and Hendricks 1950; Keenan et al. 1951; Mooney et al. 1952, 1952a; Nelson and Hendricks 1942). The external surfaces of the mica-like clay minerals and those of montmorillonite are in the same range of values, but that of kaolinite is somewhat less; the ratio of the internal to the external surface in the montmorillonites ranges from 9 to 40.