Swelling pressure of montmorillonite with multiple water layers at elevated temperatures and water pressures: A molecular dynamics study

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Yang, Yafan
Qiao, Rui
Wang, Yifeng
Sun, Shuyu

KAUST Department
Earth Science and Engineering Program
Physical Science and Engineering (PSE) Division

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The swelling of clay at high temperature and pressure is important for applications including nuclear waste storage but is not well understood. A molecular dynamics study of the swelling of Na montmorillonite in water at several temperatures (T = 298, 400, and 500 K) and water environment pressures (Pe = 5 and 100 MPa) is reported here. Adopting a rarely used setup that enables swelling pressure to be resolved with an accuracy of ~1 MPa, the swelling pressure was computed at basal spacings 1.6–2.6 nm (or 2–5 water layers between neighboring clay sheets), which has not been widely studied before. At T = 298 K and Pe = 5 MPa, swelling pressure Ps oscillates at d-spacing d smaller than 2.2 nm and decays monotonically as d increases. Increasing T to 500 K but keeping Pe at 5 MPa, Ps remains oscillatory at small d, but its repulsive peak at d = 2.2 nm shifts to ~2.0 nm and Ps at different d-spacings can grow more attractive or repulsive. At d > 2.0 nm, Ps is weakened greatly. Keeping T at 500 K and increasing Pe to 100 MPa, Ps recovers toward that at T = 298 K and Pe = 5 MPa, however, the repulsive peak at d = 2.0 nm remains the same. The opposite effects of increasing temperature and pressure on the density and dielectric screening of water, which control ion correlations and thus double layer repulsion, are essential for understanding the observed swelling pressure at elevated temperatures and its response to environment pressures.

Yang, Y., Qiao, R., Wang, Y., & Sun, S. (2020). Swelling pressure of montmorillonite with multiple water layers at elevated temperatures and water pressures: A molecular dynamics study. Applied Clay Science, 105924. doi:10.1016/j.clay.2020.105924

The authors greatly thank the support from King Abdullah University of Science and Technology (KAUST), Saudi Arabia through the grants BAS/1/1351-01-01 and URF/1/4074-01-01. The authors thank Mr. Do Yoon Moh for computing the dielectric constants of water at elevated temperatures. R.Q. acknowledge the support by US DOE through grant DE-NE0008806.

Elsevier BV

Applied Clay Science


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