14), and Gan (15) concluded that the heat of immersion
The enthalpy changes, DH, in suspensions of Li-, Na-, and depends on hydration of the particle surfaces as well as K-montmorillonite were determined as functions of the molal hydration of the exchangeable cations. Van der Marel (16) concentrations of LiCl, NaCl, and KCl, respectively, by microcapointed out that the surface area of a clay is of more imporlorimetry. These changes were compared with the corresponding tance in determining the heat released than the amount of changes in interlayer distance, l, as determined by X-ray diffracexchangeable cations. Heat of wetting and specific surface tion. It was found that DH values accompanying the collapse of are directly related. Gan (15) found that the energy required the montmorillonite layers from l ú 14 nm to l à 1.0 nm (or 0.6 to separate the particles reduces the heat of immersion signm for K-montmorillonite) were essentially negligible; however, nificantly, especially for planar particles. To our knowledge, DH values accompanying the collapse of layers of Li-and Namontmorillonite from l à 1.0 nm (three-water-layer hydrate) to however, there have been no definitive studies that have l à 0.6 nm (two-water-layer hydrate), and the collapse of layers separated the different contributions to the heat of immerof K-montmorillonite from l à 0.6 nm (two-water-layer hydrate) sion. Therefore, we conducted the present study to try to to l à 0.3 nm (one-water-layer hydrate), were not negligible. No accomplish this separation. additional collapse of Li-and Na-montmorillonite layers occurred after l à 0.6 nm, and for K-montmorillonite layers after l à 0.3 nm, but DH continued to change with increasing salt MATERIALS AND METHODS addition. This change was attributed to the penetration of electrolyte into the interlayer space. A notable observation was that the Clay Minerals value of DH was positive for Li-montmorillonite, but negative for Na-and K-montmorillonite. These observations were inter-Raw clay (montmorillonite from Upton, Wyoming) suppreted to mean that DH changes in the montmorillonite suspenplied by American Colloid Company was used to prepare sion were largely attributable to reorganization of the interlayer space by the added electrolytes.