Swelling pressure of Na- and Ca-montmorillonites in saline environments: A molecular dynamics study

The swelling pressure of bentonite clay is an important characteristic that influences its use in nuclear waste disposal repositories. A molecular dynamics study was performed to investigate the influence of salt solutions of different concentrations on the swelling pressure of Na-montmorillonite and Ca-montmorillonite in NaCl and CaCl2 solutions, respectively. Na-montmorillonite shows a gradual increase in swelling pressure as the dry density increases, while Ca-montmorillonite shows a slow increase as the dry density increases, after which a steeper increase in swelling pressure was observed. There is an overall decrease in swelling pressure of Na- and Ca-montmorillonites as the salinity of the surrounding solution increases. The influence of ionic strength was most prominent for Na-montmorillonite at moderate to high dry densities. At low to moderate dry densities, the swelling pressure of Na-montmorillonite was greater than that of Ca-montmorillonite; however, at high dry densities and ionic strengths, Ca-montmorillonite exhibits the higher swelling pressures.