A discrete element model for kaolinite aggregate formation during sedimentation

The formation of colloidal aggregates during sedimentation is an important process when considering geotechnical and environmental engineering problems including wastewater treatment systems and slurry wall constructions for waste isolation. In this paper, a quasi three-dimensional discrete element framework is developed to model aggregate formation during sedimentation by considering the following microscopic inter-particle forces present in the clay–water–electrolyte system: van der Waals attraction, electrical double-layer repulsion, Born's repulsion, hydrodynamic viscous drag, and gravity. The role of these physico-chemical forces in the formation of clay clusters during sedimentation is investigated using an integrated numerical and experimental approach. The discrete element method (DEM) framework has been previously shown to accurately model clay behavior at the microscopic level. The model is validated with experimental data for comparison of distributions of aggregate density and aggregate size. Good agreement between the model prediction and the experimental results is obtained, suggesting that the DEM can be a powerful tool to better understand the aggregate formation process at the microscopic scale. For particle sizes ranging from 0.05 to 1 µm it is also shown, through numerical simulations, that ionic strength of the fluid medium is the controlling factor for aggregate size and density and that at aggregate sizes less than 20 µm, face-to-face interactions dominate the force regime between a pair of particles. Copyright © 2007 John Wiley & Sons, Ltd.

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