An Investigation of the Swelling Kinetics of Bentonite Systems Using Particle Size Analysis

Particles size distribution (PSD) is introduced as a tool for analysis of bentonite aggregation and swelling kinetics. Raw Ca-bentonite was purified using a combined wet sieving and sedimentation processes, followed by thermochemical treatment with Na₂CO₃ to increase its swelling capacity. The detailed analysis of the PSD shows a strong correlation between the PSD and the swelling process. For the chemically treated raw bentonite, PSD revealed two different peaks representing unswelled and swelled particles along with some aggregates. The swelling is shown to be a kinetically controlled process that depends on time, temperature, and bentonite chemical composition. At the beginning of the chemical treatment, the effect of aggregates was more dominant; therefore, the viscosity did not increase much with particle size. However, the combined chemical and thermal treatment has enhanced the Na-activation process and boosted bentonite swelling. The rheological measurements have shown enhancement in the viscosity and confirmed the PSD findings. The same optimal treatment conditions are obtained from both rheological measurements and PSD analysis. A model is developed based on classical reaction rate kinetics and used to describe the conversion from unswelled to swelled particles. The PSD has a strong correlation with the physical properties of the suspension such as the viscosity. The swelling rate fits a second order model with a rate constant, k, in the range 0.002 to 0.124 h⁻¹ and an activation energy, E, of 87 kJ/mol. PSD analysis together with the developed kinetic model are powerful tools for studying the swelling kinetics of bentonites.