Size and charge constraints in microaggregation: Model experiments with mineral particle size fractions

Abstract In natural soil systems the mass ratio of clay minerals and Fe oxides is decisive for aggregate formation and stability but little information exists on the importance of size constrains in microaggregation. Therefore, we determined the aggregation kinetics of mono- and dual-mineral mixtures at pH 6 by dynamic light scattering, using three size fractions of model minerals (goethite and illite). Aggregates were characterized by scanning electron microscopy (SEM), and measured for zeta potential (ζ), surface chemical composition by X-ray photoelectron spectroscopy (XPS), and specific surface area (SSA). Destabilization experiments using sonication revealed the stability against dispersion. Aggregation occurred in all homoaggregation experiments, particularly for fine illite ( pzc ) of respective mineral mixtures. Surface chemical analysis, N 2 gas adsorption, and SEM showed that the illite surfaces were largely covered by goethite layers and clusters. Illite-goethite heteroaggregates were most stable at their pzc , whereas homoaggregates were generally less stable. Our study suggests a primary role of the