Manipulating the sedimentation of Kaolinite clay suspensions through charge interactions

Clay minerals are present in many natural (landslides, river channels) and industrial processes (ceramics, cosmetics, oil recovery). They are plate shaped charged colloids and exhibit different rheological properties than suspended hard-sphere colloids, e.g. thixotropy and shear-banding. Kaolinite clay platelets are easily found in nature and when suspended in liquids, they possess non-zero yield stress at low concentrations, indicating that the particles structure themselves through attractive interactions. Here, sedimentation of kaolinite suspensions in water are performed as a model system for geophysical flows. Using salts (NaCl and (NaPO₃)₆) to manipulate particle interactions from attractive to repulsive, we manipulate the sedimentation behavior from hard-sphere to gel-like behavior. Rheological experiments show that the repulsive kaolinite suspensions are Newtonian, while introduction of attraction leads to non-Newtonian behavior and flow hysteresis. Knowing that phosphate and chloride salts are common in nature, these observations provide insights for geophysical flows, like particulate gravity currents or the erosion threshold for cohesive river banks.