Modeling the competitive sorption and transport of Ni(II) and Zn(II) in soils: Comparing two multicomponent approaches

Authors: Padilla, Joshua - Josh; SELIM, H - Louisiana State University; GASTON, LEWIS - Louisiana State University

Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2022
Publication Date: 11/15/2022
Citation: Padilla, J.T., Selim, H.M., Gaston, L.A. 2022. Modeling the competitive sorption and transport of Ni(II) and Zn(II) in soils: Comparing two multicomponent approaches. Journal of Contaminant Hydrology. 252. Article 104108. https://doi.org/10.1016/j.jconhyd.2022.104108.
DOI: https://doi.org/10.1016/j.jconhyd.2022.104108

Interpretive Summary: The mobility of contaminants in soil is controlled by reactions between the contaminant and the soil surface. These reactions can be affected by the presence of other chemicals in the soil solution and must be accounted for to accurately model the behavior of a given contaminant in the environment. In this study, soils were reacted with solutions containing a range of nickel (Ni) concentrations in the presence of a range of zinc (Zn) concentrations, and vice versa. When Ni and Zn were both present in solution, the retention of either chemical by soil was reduced, indicating that the mobility of both solutes would be expected to increase. To determine if this was the case, Ni and Zn were applied to soil columns individually and as a mixed solution. When applied together, the mobility of both Ni and Zn was greater than when applied separately. A new model was introduced that could accurately describe the retention of Ni and Zn by soils, as well as the transport of both solutes through soil columns. This new model was compared to an older, commonly used modeling approach and provided a better description of the observed data. The advantage of the new model is that it can account for the effect of Zn on Ni mobility in soils, and vice versa, and requires a small number of easily obtained parameters.

Technical Abstract: The mobility of contaminants in soil is controlled by sorption reactions which can be affected by the presence of other solutes that compete for sorption sites. The ability to model such effects is necessary for evaluating the environmental risk of a given contaminant. In this study, the competitive sorption and transport of nickel (Ni) and zinc (Zn) in Olivier and Windsor soils was investigated using batch equilibration and miscible displacement experiments. During batch experiments, the sorption of Ni and Zn was mutually reduced in multicomponent systems, indicating that the metal cations compete for sorption sites. When applied concurrently, the retardation of both ions decreased and peak effluent concentrations increased relative to single ion experiments, demonstrating that competition increased the mobility of both ions during miscible displacement experiments. A novel Freundlich-type multicomponent isotherm (CDI) and its kinetic analog (CDIT) were developed and compared to the commonly used SRS isotherm and SRS-based kinetic approach (SRST) in describing the experimental data. The CDI provided a superior description of the competitive batch data, especially at low surface coverage, and may therefore be more applicable to multicomponent sorption than the SRS. The Olivier and Windsor transport data were best described by the CDIT and SRST, respectively, however, both models generally described the data well. Since both approaches gave comparable descriptions of the transport data while the CDI outperformed the SRS in describing the batch data, the CDI/CDIT may be more generally applicable to multicomponent systems and warrants further study.