A molecular dynamics study on the impact of isomorphic substitution on the interaction between illite and colloidal alumina in laterite

Abstract Research on the special engineering properties of laterite has highlighted the importance of interactions between colloidal oxides and clay minerals, yet their exact microscopic mechanisms remain elusive. To address this, this study employs molecular dynamics simulations to investigate the impact of isomorphic substitution on the interactions between illite and colloidal alumina. The stable configurations and the potential of mean force for these interactions were determined. The simulation results reveal that the heterogeneous charge distribution across the surfaces of illite and colloidal alumina underpins their interaction. Specifically, the negatively charged {001} surface of illite forms a stable adsorption structure with the positively charged Al atoms of colloidal alumina. Meanwhile, equilibrium cations (K + ) and atoms from isomorphic substitution induce electrostatic attractions with O and Al atoms in colloidal alumina, leading to two localized stable states and an intermediate transition state on the {00-1} surface of illite. Furthermore, Mg substitution in the octahedral sheet and Al substitution in the tetrahedral sheet reduce the layer charge density, thereby weakening the affinity of the illite {00-1} surface for colloidal alumina. Conversely, Fe substitution in the octahedral sheet increases the local charge density, enhancing the attraction of the {001} surface. These simulation results provide molecular-level insights into the mechanisms governing the behaviour of laterite, offering a theoretical foundation for guiding future experimental studies and for the engineering application and performance control of laterite soils.