Clay minerals distribute widely in soil and sediments, and play crucial roles in transport and retention of heavy metal cations. They are widely applied as adsorbent materials in environmental engineering and have been considered as backfill materials in geological disposal sites for nuclear wastes. Lots of experiments have focused on the adsorption of cations on clay minerals. However, owing to many factors these studies cannot give atomic-scale information, which greatly limits the understanding of relevant interfacial processes. Therefore, it is imperative to uncover the underlying adsorption mechanism by theoretical methods.
In the pursuit of a microscopic understanding of the complexation of heavy metal cations on clay edges, systemic first principles molecular dynamics (FPMD) simulations were conducted to investigate Ni(II) complexes on edge surfaces of 2:1-type phyllosilicates. With constrained FPMD and pKa calculation method, the complexation mechanism of Ni(II) is derived, including complexing structures, free energies, and the protonation states of surface complexes. These results are useful in future experimental and modeling researches, e.g., in interpreting experimentalobservations and building theoretical models.