Sorption and Selectivity Sequences of Cd, Cu, Ni, Pb, and Zn in Single- and Multi-Component Systems in a Cultivated Chilean Mollisol

Abstract

The heavy-metal sorption ability of soils is one of the most important factors that determine the fate of these contaminants in this medium of the biosphere. When heavy-metal containing soil amendments are land applied, a multi-component soil-solution equilibrium may occur in which various metals compete simultaneously for the sorption sites on the soil particles. In order to determine the effect of competition among Cd, Cu, Ni, Pb, and Zn on sorption characteristics and the selectivity sequence of those heavy metals in a cultivated Mollisol of central Chile, batch sorption experiments were carried out in single- and multi-component systems. Heavy metal sorption isotherms in both types of system were well described by the Langmuir's equation. For all the metals evaluated, competition among them (multi-component system) decreased both the maximum sorption capacity, obtained from the Langmuir's isotherm, and the partition coefficient (K_d) compared to the single-component system. In addition, the simultaneous presence of the five metals promoted the sorption of Cd, and to a lesser extent of Ni, on more specific sorption sites of soil particles. Either in single- or multi-component system, Pb and Cu showed a higher selectivity and retention compared to Cd, Ni and Zn, which indicates that the later heavy metals would present a higher mobility in the soil-plant-water system. Since Langmuir's parameters and K_d were highly affected by competition for all heavy metals evaluated, the use of single-component parameters in modeling assessment might lead to an incorrect description of the transport and fate of these contaminants in receiving Mollisols.

Keywords:

• competitive interaction
• heavy metal
• Langmuir's model
• partition coefficient
• sorption isotherm

Acknowledgments

This work was supported by FONDECYT (National Fund for Scientific & Technological Development) under project number 1070116 (Chile). Mauricio Molina would like to acknowledge PUC-MECESUP (0210) doctoral scholarship. The authors thank the reviewers for their comments and helpful suggestions to improve the manuscript.