Invasion of Pb2+ into montmorillonite-illite clay and the response of interlayer K+ and water

Abstract The soil environment is encountering a serious threat from heavy metal contamination (e.g., Pb2+). However, it is still unclear what actually happens following the invasion of Pb2+ into soils, especially on the molecular scale. In this study, the molecular dynamics method was used to exclusively determine the influence of Pb2+ invasion on the swelling properties of montmorillonite-illite clay (Mt/I) and the stability of interlayer K+ and water. The model of Mt/I was constructed to simulate a situation similar to the real natural environment. The invasion of Pb2+ energetically promoted the hydration and swelling of the mixed clay, which may, in turn, further increased the risk of Pb2+ penetrating into the interlayer. K+ adsorption and the stability of Pb2+ increased with increasing Pb2+ invasion, but the adsorption mode and distance to the surface were not affected. The condensation of water layers on a clay surface was regulated by the invasion of Pb2+, and in particular, Pb2+ exerted a significant effect on the orientation and hydrogen bond network of the water molecules at the illite surface. Therefore, the invasion of Pb2+ increases the stabilities of the interfacial interlayer K+ and water molecules. Our findings provide new insights into the mechanical aspects of heavy metal contamination of a clay soil environment.