Molecular insight into the transport of multicomponent heavy metals in calcium silicate hydrate and its mechanical behavior

Heavy metal-contaminated sites are primarily treated via solidification and adsorption. Calcium silicate hydrate (C-S-H) is generated during the soil stabilization process and contributes significantly to the strength and durability of the stabilized soil. To understand how the soil moisture content and heavy metal concentration affect the transport of heavy metals and the tensile strength of C-S-H, this study performed molecular dynamics (MD) simulations under different moisture and concentration levels. The results showed that Pb 2+ presented the highest adsorption to the surface of C-S-H due to its strong electrostatic interaction energy. The adsorption density peaks of Pb 2+ were 1.5–5 times greater than those of Cd 2+ and Zn 2+ . Zn 2+ and Cd 2+ ions were more likely to be adsorbed onto water molecules and form a larger hydrated radius than Pb 2+ . The adsorption of heavy metals onto C-S-H initially increased as the metal concentration increased and then decreased because of the limited sorption sites on C-S-H. The diffusion coefficients of the multicomponent metals in C-S-H showed no consistent trends. The maximum tensile strength of C-S-H decreased with increasing soil moisture and heavy metal concentrations. The tensile stress increased approximately linearly with strain until it reached a peak, after which it gradually declined but remained above zero, indicating good ductility and toughness under unsaturated conditions. These findings offer valuable molecular insights into the interactions between C-S-H and heavy metals and soil moisture, thereby advancing our understanding of their combined effects on soil stabilization.