Incorporating Primary Aggregate Heterogeneity into DLVO Theory: A Case Study on Heteroaggregation of Silica and Goethite Colloids

Colloid interactions are usually interpreted using the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and its variants. However, the repulsive interaction energy given in some DLVO predictions was sometimes inconsistent with the observed aggregation in heterogeneous colloidal systems containing different types of colloids. To address this issue, we studied the heteroaggregation of silica and goethite colloids, two oppositely charged colloids commonly found in the environment, as functions of colloid mass ratio, pH and ionic strength. We found that the discrepancies between experimental observations and DLVO predictions can be attributed to the heterogeneous surface charge distributions of the primary aggregates, contradicting the DLVO assumption of homogeneously charged primary aggregates. Consequently, a new method considering the effect of heterogeneity, was developed to quantitatively evaluate the interaction energies between primary heteroaggregates based on the electrostatic and van der Waals interactions (Hetero-DLVO). The interaction energies, evaluated by considering all pairwise interactions among the component colloids of the two primary aggregates (i.e., silica-silica, goethite-goethite, and silica-goethite), showed good agreement with experimental observations under various conditions. This study contributes to a better understanding of heteroaggregation mechanisms, improved DLVO-based prediction strategies for heterogeneous colloidal systems, and facilitates accurate predictions of colloidal particle behavior in aquatic systems.