பொருள் அறிவியல் & பொறியியல் இதழ்

Effects of Inorganic Salts Addition on Na-montmorillonite Clay at High Temperature and High Pressure: Insights from Molecular Dynamics Simulation

Abstract

Moussa Camara, Hualin Liao, Jiafang Xu, Tingji Ding, Rogers Swai and Jun Zhang

In the present work, we performed a molecular dynamics (MD) simulation of Na-montmorillonite (Na-Mt) in nonambient environment under the crystalline swelling to evaluate the effect of temperature and inorganic salts addition on the interlayer structure and the swelling behavior of Na-Mt. The activities of inorganic salts (NH4Cl, AlCl3, MgCl2 and FeCl3) on the hydration process of Na-Mt at high temperatures (200, 300, 400, 500, and 600 K) and high pressure (HTHP) of P=6 GPa in an isobaric isothermal ensemble (NPT) were investigated. The results showed that addition of inorganic salts into Na-Mt enhanced mobility of the interlayer species, and shrunk the hydration shell of the interlayer ions with a rise in temperature. The salts inhibited swelling by reducing the mobility of the interlayer species and the basal spacing. The type of cations present between the layers, their hydration energies affected the structure and properties of Na-Mt. Chlorine played an important role in the inhibition process of inorganic salts by exerting strong attractive forces on interlayer H2O molecules. Compared with the other salts, the most stable state of Na-Mt at HTHP is achieved with NH4Cl. These results could help a better understanding of the inhibition effect of inorganic salts on Na-Mt and predict the hydration process of Na-Mt at HTHP for further improvement of its structure.

Highlights

• Cl anion hydration energy change is more evident with salt type than temperature
• Inorganic salt and temperature increase shrink the hydration shell of interlayer ions
• NH4Cl addition provides a good inhibition at high temperature and high pressure
• Increasing temperature and hydration degree promote the cation exchange process