Coagulation of kaolinite colloids in high carbonate strength water

Dynamic light scattering (photon correlation spectroscopy) was used to investigate the influence of a carbonate rich groundwater on the aggregation kinetics of kaolinite clay colloids. Suspension stability was determined by the ratio of the Smoluchowski rate expression for irreversible aggregation to the experimentally determined binary aggregation rate. At solution pH of 7.8 kaolinite particles were stable in electrolyte, NaCl, concentrations below 100 mM. Charge reversal of edge surfaces and double-layer compression at electrolyte concentrations exceeding 100 mM are proposed as the governing mechanisms for observed kaolinite aggregation. Edge-to-face heterocoagulation by electrostatic attraction was not observed. Implication for facilitated contaminant transport in carbonate rich groundwater is discussed.