Molecular Simulations of Swelling Clay Minerals

Abstract

We have carried out molecular simulations in the grand-canonical ensemble of water and cations in Wyoming and Arizona montmorillonite clay minerals, with varying relative humidity. Several water models and cations are used to investigate the swelling of these clays. We show how the water content depends on the type of clay, type of cation, the basal spacing, and the relative humidity. Related to the layering of water molecules in the interlayer space, the pressure normal to the clay sheets oscillates as a function of the basal spacing. Minima in corresponding free energy curves indicate the presence of dehydrated states and layered hydrates. The development of these stable states and the corresponding basal spacings are in agreement with experimental data. Density profiles show significantly different interlayer structures depending on the type of clay and models used. We show a relation between formation of two-layer hydrates and the position of the cations. The simulations with the MCY water model underestimate the spacings of two-and three-layer hydrates, whereas our simulations with the TIP4P model produce a better agreement. Therefore, we recommend the TIP4P model for simulating clay minerals. In addition, we report remarkable ordering of cations and water molecules in a one-layer Arizona montmorillonite hydrate.

Structure and dynamic properties of water saturated CTMA-montmorillonite: molecular dynamics simulations

“…One with a cation exchange capacity (CEC) of 106 mequiv/100 g is obtained from Inner Mongolia, China (abbreviated M-Mt) on the basis of previous experimental study (Zhu et al, 2008a). The other Mt model with a larger CEC of 131 mequiv/100 g is the Arizona-type Mt (abbreviated A-Mt) (Tambach et al, 2004 4 , respectively where X represents monovalence interlayer compensator cations. In these Mt models, the isomorphic substitutions obey Loewenstein's rule (Loewenstein, 1954).…”

Hydration of methane intercalated in Na-smectites with distinct layer charge: Insights from molecular simulations

“…Garfield-type nontronite only bears tetrahedral charges [20], Arizona-type montmollonite only has octahedral charges [21], and Wyoming-type montmollonite has both types [22] (Table 1). In these clay models, the isomorphic substitutions obey Loewenstein's rule [23].…”

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

“…Sato et al, 1992) or modelled by molecular dynamic approaches (Tambach et al, 2004;Chavez-Paez et al, 2001). The number of water layers in the interlayer depends on the nature of the interlayer cations and on the compaction degree (Kozaki et al, 1998;Ferrage et al, 2005).…”