A Thermodynamic model on the effect of salinity on the micropore structure of Na-montmorillonite

Sato, Haruo

This paper presents a thermodynamic model which can calculate the interlayer space of Na-montmorillonite based on the relative partial molar Gibbs free energy of interlayer water in the Na-montmorillonite when contacted with a solution of an arbitrary salinity. Since the interlayer space of Na-montmorillonite cannot be directly calculated thermodynamically, here the average density of the Na-montmorillonite stacks and aggregates was calculated versus salinity. Based on the calculated results of Na-montmorillonite density versus salinity, interlayer space versus salinity was estimated. The calculated average density of montmorillonite stacks and aggregates increased with salinity, and particularly the change in density was significant in the low region of the initial montmorillonite density. The initial montmorillonite density of 0.5kg/dm increased to about 1.05kg/dm at the condition of 0.5M-NaCl, meanwhile the initial montmorillonite density of 1.0kg/dm increased to about 1.16kg/dm at the same salinity. The interlayer space estimated decreased with increasing salinity, and this trend was consistent with that of measured results.