Change of b-Dimension with Swelling of Montmorillonite

Abstract

Abstract--The effect of swelling on the b-dimension of Na-saturated, Upton, Wyoming montmorillonite was re-examined using powdered silicon as an internal standard. After being corrected with reference to the internal standard, the b-dimension did not increase through the entire range of swelling as reported previously. It increased up to a water content of ~ 3.0 g/g montmorillonite and remained constant thereafter. However, the diffraction peak of the internal standard shifted towards lower angles at higher water contents. This shift was attributed to a relaxation of the wetter samples away from the knife edge of the diffractometer. Presumably, a similar relaxation occurred in the earlier study and was responsible for the apparent increase in b-dimension at water contents above ~ 3.0 g/g.The b-dimension of Upton montmorillonite saturated with different cations was determined using powdered silicon and a colloidal quartz impurity as internal standards. The water content at maximal swelling decreased as the b-dimension increased.

Quantification and comparison of the reaction properties of FEBEX and MX-80 clays with saponite: Europium immobilisers under subcritical conditions

“…3 and 4, b-f) the basal spacing of 238 bentonites was increased to 15.5 Å, in agreement with data reported for smectites saturated with 239 multivalent cations (Ravina and Low, 1977). This increase agreed with a sorption of Eu 3+ 240 equivalent to its CEC at 0 h (see Fig.…”

“…Figure 5 250 shows the XRD pattern of both bentonites after hydrothermal treatment at 80ºC for 63 days and 251 at 150ºC for 56 days. In both cases, the 2θ position of the 001 reflection indicates the basal 252 spacing of bentonites, increased up to 15.5 Å, in agreement with the sorption of Eu 3+ at no 253 specific sites (Ravina and Low, 1977). 254…”

“…Their reaction rate 189 constants, k, were also similar within the uncertainty (Table 3). k values displayed in Table 3, with the characteristic "saw-tooth" shape of the two-dimensional reflections (Warren, 1941 Ravina and Low, 1977;Warren, 1941). 237…”

Changes in the Properties of a Montmorillonite-Water System during the Adsorption and Desorption of Water: Hysteresis

“…In a dry montmorillonite, the silicate tetrahedra in the tetrahedral sheet are rotated alternately clockwise and counterclockwise in order to articulate with the alumina octahedra in the octahedral sheet (Radoslovich and Norrish, 1962) and are coordinated with the exchangeable cations occupying the ditrigonal cavities formed by the surface oxygens (Lahav and Bresler, 1973). These cations electrostrict the surrounding structure, and its b dimension therefore decreases as the crystallographic radius of the exchangeable cation decreases (Leonard and Weed, 1967;Ravina and Low, 1977). Probably, the amount of strain energy stored in the structure is increased accordingly.…”

“…In the process, the exchangeable cations move out of the ditrigonal cavities (Sposito et al, 1983), their electrostrictive influence on the surrounding structure is reduced, and the structure relaxes. Relaxation of the structure is indicated by an increase in the b dimension (Ravina and Low, 1977;Margheim, 1977). Some of the energy released in the hydration of the surfaces and cations and in the relaxation of the mineral structure is utilized to remove the cations from the ditrigonal cavities and to separate the layers against the prevailing attractive forces, but most of it is lost as heat.…”