Interactions of lignin preparations obtained by enzymatic and other processes with copper(II) and zinc(II) ions were studied. The shape of adsorption isotherms depends on the provenience of lignin. Copper(II) ions are bound more strongly than zinc(II) ions. The dependence of the sorption on pH indicates that carboxylate anions may be involved in binding of copper(II) ions, whereas phenolate groups in that of zinc(II) ions. As the binding is predominantly irreversible for both ions, ion exchange is not the predominant mechanism. The effect of neutral salts on adsorption isotherms indicates changes in the tertiary structure of lignin. Some observed adsorption isotherms are simple, others are complex, indicating the presence of two adsorption sites of different accessibility. The interaction with one or two adsorption sites depends both on the nature of the lignin used and on the metal ion involved.
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