Atomistic simulations of the swelling behaviour of Na-montmorillonite in mixed NaCl and CaCl2 solutions

Abstract

Using molecular dynamics simulations, the interlayer swelling pressure of Na-montmorillonite clay was determined at different dry densities and ionic strengths while varying the concentration of NaCl and CaCl2. The composition and charge of the interlayer ions in the clay were also analysed.When the salt composition of the surrounding environment is varied, its influence on the swelling pressure is dependent on the overall ionic strength and dry density of the clay. At low or moderate dry density, as the ionic strength percentage ratio of NaCl to CaCl2 decreases, the swelling pressure trend shows a downward slope. In addition, at high dry density, the swelling pressure increases as the ionic strength percentage ratio of NaCl to CaCl2 decreases.The composition and the total charge in the interlayer space of Na-montmorillonite clay are dependent on the ionic strength, ionic strength percentage ratio of the surrounding solution and d-spacing of the clay layers.