INFLUENCE OF SALINITY ON THE SWELLING RATE AND HYDRAULIC CONDUCTIVITY OF NA-BENTONITE AND CA-BENTONITE CLAYS

Bentonite, consisting mostly of montmorillonite, is a smectite clay formed from weathered volcanic ash. It is an absorbent aluminum phyllosilicate and due to its 2:1 ratio consisting of an octahedral hydroxide sheet sandwiched between two tetrahedral silicate sheets, bentonite clay expands when exposed to moisture. Due to use in multiple industries, the two types of bentonite clay used for this study are sodium and calcium. In this study, varying sodium chloride (NaCl) concentrations were used on each type of bentonite clay to determine salinity’s influence on swelling rate and hydraulic conductivity. X-ray Diffraction (XRD) analysis of both the sodium and the calcium bentonite samples were conducted using the Shimadzu XRD6100. Visual swelling tests were performed using a graduated cylinder and compared to the Swelling Index. Hydraulic conductivity and infiltration rate experiments were also conducted using a chromatography column. The swelling properties of bentonite are dependent on factors such as; the water absorption at platelet level, the repulsive forces of the particles, and the exchangeable ions contained in the clay. Sodium bentonite, with sodium cation prevalence (Na⁺), showed the highest rate of swelling when exposed to the control DI water which has no NaCl. The swelling capacity and barrier effects of sodium bentonite exposed to concentrations of NaCl were drastically reduced. Calcium bentonite, with calcium cation prevalence (Ca²⁺), does not show the same dramatic swelling ability of sodium bentonite. The swelling of bentonite clay leads to many challenges in the petroleum, engineering, and environmental industries and understanding the principles of bentonite clay can help resolve these challenges.