Hydration mechanisms of smithsonite from DFT-D calculations and MD simulations

Investigation on the mineral?water interactions is crucial for understanding the subsequent interfacial reactions. Currently, the hydration mechanisms of smithsonite are still obscure. In this paper, the adsorption of H₂O at different coverage rates on smithsonite (1 0 1) surface was innovatively investigated using density-functional theory (DFT) calculations and molecular dynamics (MD) simulations by analyzing adsorption model, interaction energy, atomic distance, density of state, electron density difference, concentration profile, radial distribution function and self-diffusion coefficient. We found that single H₂O preferred to be dissociated on smithsonite (1 0 1) surface via the interaction of surface Zn with the Ow of H₂O and H-bond between Hw of H₂O and surface Os. However, dissociation adsorption and molecular adsorption coexisted on the smithsonite surface at a high coverage rate of H₂O, and dissociation adsorption remained the main adsorption mechanism. Moreover, we found the interaction between smithsonite surface and H₂O was weakened as a function of H₂O coverage, which was because the presence of interlayer H₂O and different layers of H₂O decreased the reactivity of the smithsonite surface. The H₂O is mainly adsorbed on the smithsonite surface by forming three layers of H₂O (about 10–15 Å), with the ordering degree gradually decreasing.