Influence of Associated Cations on the Transport and Adsorption of Chloride Ions in the Nano-channel of Calcium Aluminosilicate Hydrate Gel: A Molecular Dynamics Study

Abstract

Molecular dynamics simulation was utilized to investigate the transport and adsorption of chloride in the nanopore of calcium aluminosilicate hydrate (C-A-S-H) with associated cation types of Ca, Mg, Na and K. The local ionic structure, atomic dynamics and bond stability were analyzed to elucidate the interaction between cations and chloride ions. The results show that interfacial chloride is absorbed through the ion pairing formation in the vicinity of C-A-S-H substrate. Interfacial cations can simultaneously interact aluminosilicate chains, water molecules and Cl⁻ ions, which restrict the motion of interfacial Cl⁻ ions. Pore solution chloride can be immobilized through the solvation effect of cations. Cations along with their hydration shell can connect to neighboring Cl⁻ ions to decrease their mobility. Owing to the varied ionic chemistry, cations show different interaction strength with neighboring water molecules and anions, which determines the chloride transport behavior in the nanopore of C-A-S-H. The chloride immobilization capacity of C-A-S-H nanopore with different associated cations is listed in following order: Mg²⁺<Ca²⁺<Na⁺≈K⁺, which agrees reasonably with previous experiments.

Keywords

calcium aluminosilicate hydrate / nanometer channel confinement / chloride immobilization / associated cations / ionic structure