Charge Properties, Characteristics and Applications of Bentonite: A Concise Review

Abstract

Bentonite belongs to the smectite group of clay with montmorillonite as the primary subunit. Calcium and sodium bentonite are the two common types of bentonite which are used in various fields. As a filler material, surface modification is usually necessary to make bentonite more compatible with matrix materials. During the modification process, elemental additives can intercalate between the clay layers, promoting layer exfoliation. This results in a filler material with very high specific surface area-to-weight ratio. Consequently, even at low filler loading the resulting composites can exhibit significant improvements in mechanical and thermal properties. In aqueous environments, sodium bentonite swells more than its calcium counterpart due to the weaker interlayer bonding by monovalent Na⁺ ions as compared to the stronger divalent Ca²⁺ ions. High water uptake could be advantageous in agriculture is but generally regarded as disadvantageous in separation processes such as wastewater treatment and oil & gas drilling exploration. Based on its wide availability, abundance and cost effectiveness, bentonite and other smectite clays are expected to attract more interest in the future. In addition, with various sustainability goals outlined by the United Nations, the use of natural materials like bentonite is projected to expand particularly in countries with substantial natural reserves.