Modeling Sorption of Cd, Hg and Pb in Soils by the NICA-Donnan Model

Abstract

Metal adsorption is an important process at the soil-solution interface that controls metal bioavailability and toxicity. In this study, batch adsorption experiments were conducted to investigate the binding of Cd, Hg and Pb in soils collected from around metal smelters in Quebec and Ontario, Canada. It was found that soil organic matter enhanced the retention of Cd, Hg and Pb. Assuming that the surfaces of soil particles behaved similarly to organic matter, we used the Non-Ideal Competitive Adsorption (NICA)-Donnan model to derive the parameters for surface complexation of the three metals. The shape of the Cd, Hg and Pb adsorption isotherms are briefly discussed with respect to the results of the experimental measurements and the model predictions. The average values of the NICA-Donnan model parameters could be used to give reasonable predictions of metal sorption in the soils of this study.

Keywords:

• Trace metals
• soil contamination
• adsorption
• thermodynamic equilibrium
• modeling.

We are thankful to Hélène Lalande for her assistance in chemical analyses. The financial support for this project from the Natural Sciences and Engineering Research Council of Canada–Metals In The Environment Research Network (NSERC-MITE-RN), Toxic Substances Research Initiative (TSRI) of Health Canada and a doctoral scholarship from “Fonds québécois de la recherche sur la nature et les technologies” (formerly FCAR) are greatly acknowledged.