Revealing crucial effects of temperature and salinization on swelling behavior of montmorillonite

Thermal and saline environment significantly affects the swelling behavior of montmorillonite (Mt) that is crucial for the safety of engineering barrier. However, the swelling mechanism of Mt under non-isothermal and saline environment remains poorly understood. A molecular Na-Mt model is proposed to analyze the swelling pressure change of Mt under various non-isothermal and saline conditions. The swelling mechanism of Mt at various salt solutions and temperatures is discussed based on analyses of the water concentration profile, hydration energy of Mt-salt solution system, and hydration state of interlayer cations. We find that the critical temperature that differentiates the negative and positive correlations between swelling pressure of Mt and temperature under different saline environments coincides with the hydration state saltation temperature identified from radial distribution function. Our research shows that the hydration energy of Mt and the hydration state of interlayer cations jointly control the swelling of Mt, via governing the water migration in Mt-salt solution system.