Flocculation Kinetics and Cluster Morphology in Illite/NaCl Suspensions

Using static and dynamic light-scattering techniques, we investigated the flocculation of geologic specimen illite and soil illite colloids suspended in NaCl solution at pH 8. Our results show that the two universality classes proposed by Lin and co-workers to characterize the diffusion and reaction-limited régimes of cluster-cluster flocculation do not apply to illite colloids, which have nonspherical morphology. Static light-scattering measurements yielded mass fractal dimensions for the soil illite clusters that were significantly above those required by universality. Those for specimen illite were influenced by the initial colloid concentration, suggesting that cluster restructuring had occurred during flocculation. Dynamic light-scattering measurements revealed a significant departure from linear growth of the mean cluster size with time, as required by universality in the diffusion-limited régime, and, for specimen illite, an oscillatory dependence of the mean cluster radius on time was observed in the transition from diffusion-limited to reaction-limited flocculation. Overall, the morphology, interactions, and restructuring of primary particles are believed to be responsible for the departure from universality in the flocculation behavior of the illite colloids. Copyright 2000 Academic Press.