Modeling the kinetics of competitive sorption and desorption of Zn(II), Ni(II), and Pb(II) in an acidic soil: Stirred‐flow experiments
Joshua T. Padilla, H. M. Selim
Abstract
Abstract The mobility and fate of heavy metals in soils is of environmental concern. Stirred‐flow experiments were conducted to study the competitive sorption and desorption of Zn, Ni, and Pb in binary systems in acidic Olivier loam soil. For all three binary systems, consecutive pulse applications demonstrated that the metal of highest affinity displaced sorbed amounts of metals of low affinity, whereas sorbed concentrations of the ion of highest affinity were unaffected by the addition of the metal of lower affinity. The displacement of Ni by Zn appeared irreversible, whereas the displacement of Zn by Pb and Ni by Pb was reversible. A two‐site competitive kinetic model consisting of common and ion‐specific sites successfully described the experimental data. Specifically, the model was able to accurately predict lower sorbed concentrations in concurrent pulse studies, as well as the displacement of Ni by Zn and Zn by Pb in the consecutive pulse studies. The presented model provided significant improvement over single‐ion models that have been previously used to describe competitive interactions between species in stirred flow experiments.