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Metal ion binding to humic substances: application of the non-ideal competitive adsorption model

Metal ion binding to humic substances: application of the non-ideal competitive adsorption model

Environmental Science and Technology 29(2): 446-457

The application of a new model to describe metal ion binding by humic acids is discussed. Metal ion binding is always of a competitive nature since the proton is always present. Although of great practical importance, the combination of a chemically heterogeneous system with competitive binding poses difficult problems from both experimental and theoretic points of view. The new Non-Ideal Competitive Adsorption model (NICA model) used here is able to account for the non-ideal binding to heterogeneous ligands. A good description of the binding of H, Ca, Cd, and Cu to a purified peat humic acid is achieved over a wide range of free metal ion concentrations (-2 gt log Me-2+ gt -14) and pH (2 lt pH lt 10). The results show that binding of metal ions to humic acid is strongly influenced by the intrinsic chemical heterogeneity of the humic material itself as well as by ion-specific non-ideality. The results indicate that copper competes much more efficiently with protons bound to the phenolic type groups than calcium and cadmium.

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Accession: 009014706

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PMID: 22201392

DOI: 10.1021/es00002a022

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