Adsorption mechanism of Pb in montmorillonite nanopore under various temperatures and concentrations.

Adsorption of lead (Pb) onto the montmorillonite (Mt) surface is one of the key approaches to remove Pb in geological and environmental engineering. Temperature and initial Pb concentration are two essential factors that influence the adsorption capacity of Mt on absorbing Pb. However, the nanoscale governing mechanism of temperature and initial concentration on Pb adsorbing of Mt is still unclear. This research performed comprehensively molecular dynamics (MD) simulations to investigate how temperature and initial concentration affect the dynamic Pb adsorption of Mt nanopore. The Pb removal ratio shows a two-stage variation with the increase of initial Pb concentration. Temperature controls the maximum initial Pb concentration for complete Pb removal by changing the maximum adsorption energy of Mt. Temperature also influences the maximum adsorption capacity and Pb removal ratio of Mt nanopore indirectly by changing diffusion and hydration state of Pb. The initial Pb concentration corresponding to the maximum adsorption energy coincides with the maximum initial Pb concentration determined by the Pb removal ratio. Lower adsorption energy and higher level of hydration and diffusion make Pb absorbing on Mt surface become more difficult, reducing the Pb adsorbing capacity of Mt. The initial Pb concentration influences adsorption capacity and Pb removal ratio not only via altering the quantity of Pb but also through controlling the adsorption energy of Mt, as well as the diffusion and hydration state of Pb. With the increase of initial Pb concentration, the hydration of Pb is weakened while the adsorption energy of Mt and diffusion of Pb are enhanced.