Effect of layer charge on the crystalline swelling of Na⁺, K⁺ and Ca²⁺ montmorillonites: DFT and molecular dynamics studies

Abstract

The swelling and cation exchange properties of montmorillonite are fundamental in a wide range of applications ranging from nanocomposites to catalytic cracking of hydrocarbons. The swelling results from several factors and, though widely studied, information on the effects of a single factor at a time is lacking. In this study, density functional theory (DFT) calculations were used to obtain atomic-level information on the swelling of montmorillonite. Molecular dynamics (MD) was used to investigate the swelling properties of montmorillonites with different layer charges and interlayer cationic compositions. Molecular dynamics calculations, with CLAYFF force field, consider three layer charges (−1.0, −0.66 and −0.5 e per unit cell) arising from octahedral substitutions and interlayer counterions of Na, K and Ca. The swelling curves obtained showed that smaller layer charge results in greater swelling but the type of the interlayer cation also has an effect. The DFT calculations were also seen to predict larger d values than MD. The formation of 1, 2 and 3 water molecular layers in the interlayer spaces was observed. Finally, the data from MD calculations were used to predict the selfdiffusion coefficients of interlayer water and cations in different montmorillonites and in general the coefficient increased with increasing water content and with decreasing layer charge.

Effect of Crystal Chemistry Properties on the Distribution Characteristics of H2O and Na+ in Na-Montmorillonite Interlayer Space: Molecular Dynamics Simulation Study

“…The pictorial diagram about the coordination number and Van der Waals radius of Na + are shown in Figure 13. This research result is in line with the conclusions acquired by Sun et al and Seppälä et al [6,50]. Besides, the strength of the main peak of the g(Na-Ow) increases gradually with the decrease of layer charge density.…”

The Role of Clay Swelling and Mineral Neoformation in the Stabilization of High Plasticity Soils Treated with the Fly Ash- and Metakaolin-Based Geopolymers

“…It follows that Ca 2+ released from the MK solution was consumed entirely during the process of cationic exchange between the soil solution and montmorillonite exchangeable sites at OMC. The newly released alumina did not exercise any major impact on the diffraction pattern of montmorillonite in the soil treated with MKG, which is in line with the current experimental and modeling studies favoring the major impact of the nature and type of interlayer cations, as well as their hydration states, on XRD intensities of clay minerals [34,35]. XRD reflexes of quartz showed reduced intensities following the addition of MKG and FAG in OMC and saturation conditions compared to the natural soil (Figures 4 and 5).…”

A review of molecular dynamics simulations in the designing of effective shale inhibitors: application for drilling with water-based drilling fluids

“…Similar swelling behavior with increasing layer charge due to the significant number of interlayer cations and greater ion hydration enthalpies was reported by Yi et al (2018). Even so, opposite claims were made by Greathouse and Sposito (1998) and Seppälä et al (2016). They indicated that Mt with lower layer charges experiences more significant swelling than one with a higher charge.…”

“…However, Tao et al (2010) showed that Na-Mt overall swelling was higher than that of Ca-Mt and K-Mt. Still, however, it is essential to note that the higher the valence, the higher the cation's hydration energy (Hensen et al 2001;Li et al 2019;Seppälä et al 2016).…”