Effect of pH-modifiers on the rheological behaviour of clay slurries: Difference between a swelling and non-swelling clay

Abstract

Owing to their anisotropic surface charge and anisometric shape aqueous clay slurries are known to exhibit rich rheological behavior with the existence of yield stress at very low solids concentrations which can be modulated using different pH modifiers. The impact of particle-particle association on the rheological behaviour of two different clays, a swelling 2:1 (bentonite) and a non-swelling 1:1 clay (kaolin) was investigated. Effect of factors such as pH, pH modifiers, and solids concentration on the rheological behaviour was studied using Small Amplitude Oscillatory Shear (SAOS) and shear rheology. For kaolin, the microstructural strength as measured using storage modulus (G′) was reflected directly in the high shear response. However, for bentonite the high shear viscosity evolved non- monotonically as a function of G′ which was connected to its swelling behaviour. Cohesive energy density increased sharply as a function of volume fraction for bentonite compared to kaolin and may provide a basis for the stark contrast in industrial unit operation response of the two clays. The results highlight the importance of using several rheological material functions to understand the true microstructure of clay dispersions.