Thermodynamic assessment of the variation of the surface areas of two synthetic swelling clays during adsorption of water

Abstract

Two synthetic smectites (montmorillonite and beidellite) are studied by a water adsorption technique in order to assess their specific surface areas under atmospheric conditions. A route recently proposed for extracting the thermodynamic data from experimental adsorption isotherms is used. The variation of the specific surface area during water adsorption is obtained, which can be linked to the enlargement of the interlayer space determined using X-ray diffraction. This variation is compared to an idealized specific surface area obtained from TEM and X-ray measurements in agreement with crystallographic models. All these results are also compared with those obtained previously for a natural montmorillonite. A simple view of swelling is proposed.

Mechanism of methylene blue removal from water by swelling clays

“…In a previous study, the SSA of a montmorillonite measured by water adsorption was 126 and 260 m 2 /g at relative vapor pressure P/P 0 of 0.1 and 0.8 with a mean layer thickness of 4.76Å in contrast to N 2 -BET ESA of 44 m 2 /g [33]. Three adsorption plateaus were found for a similar Na-montmorillonite at 10, 30, and 60% RH, resulting in SSA of 80, 150, and 200 m 2 /g, respectively [33]. Using these SSA measured by water adsorption, the area occupied per MB molecule will be 14-46Å 2 , still less that the contact area of 55Å 2 using the 17.0Å × 3.25Å face of MB and much less than 130Å 2 per MB molecule lying parallel to the montmorillonite surfaces [14].…”

“…The SSA is a function of RH and thus, can be determined by measuring water adsorption [32]. In a previous study, the SSA of a montmorillonite measured by water adsorption was 126 and 260 m 2 /g at relative vapor pressure P/P 0 of 0.1 and 0.8 with a mean layer thickness of 4.76Å in contrast to N 2 -BET ESA of 44 m 2 /g [33]. Three adsorption plateaus were found for a similar Na-montmorillonite at 10, 30, and 60% RH, resulting in SSA of 80, 150, and 200 m 2 /g, respectively [33].…”

Hydration sequence of swelling clays: Evolutions of specific surface area and hydration energy

“…From these values of n m , the specific surface area can be determined by assuming that the cross-sectional area of the water molecule for the montmorillonite is 12 Å 2 [41,53]. The specific surface area deduced from such calculations is given in Table 1 for each studied cation.…”

Study of the influence of location of substitutions on the surface energy of dioctahedral smectites

“…6. Basically, the separation of particles, implying the increase of the surface area and the increase of the interlayer distance, appears sooner for the synthetic montmorillonite than for the synthetic beidellite (X-ray experiments with comparable synthetic samples and synthesis are described elsewhere [41]). However, such a basic relation must not be generalized, because a lot of forces are acting during swelling.…”