Modeling the transport behavior of Pb(II), Ni(II) and Cd(II) in the complex heavy metal pollution site under the influence of coexisting ions

Complex metal contaminated sites are generally more harmful than single metal contaminated sites. Therefore, this study combined experiment and mathematical model to investigate the migration of Pb(II), Ni(II) and Cd(II) in single and multi-metal systems. The data from batch and column experiments were fitted well by Langmuir and nonequilibrium convection-dispersion equation. In the single metal system, the adsorption capacity of metals in soil was Pb> >Cd>Ni. In multi-metal systems, Pb(II), Ni(II) and Cd(II) retention in column decreased by 42.8%, 56.2% and 92.8% respectively due to the competition effect. The competitive effect enhanced the migration of three metals in the column. Ni(II) and Cd(II) showed irregular breakthrough curves , called “overshooting”, under the effect of Pb(II). The phenomenon of overshooting made the outlet concentration C of the column greater than the inlet concentration C 0 ( C / C 0 >1), leading to serious potential risks to groundwater. In addition, results from speciation of metals showed that the competition effect and overshooting mainly occurred in exchangeable and carbonate fractions. Understanding the transport of metals in complex contaminated sites is important for risk assessment.