The lability of copper ions sorbed on humic acid

Abstract

AbstractInteraction between copper (II) ions and humic acids can yield at least three different types of complex. The soluble forms promote migration of the metal ion in environmental systems and the labile content can be more ‘biologically active’. In our study, the distribution of copper between ‘fixed’, ‘non-labile’ and ‘labile’ complex forms at different pH values has been evaluated by equilibrating Cu-loaded humic acid with ion exchange resins of different types (and counter ion forms). Metal loadings of 35 to 225 μmol g−1 were obtained by equilibrating 10 or 50 mg of purified acid with Cu (II) solutions (10−4 M, pH 2 to 4.5). After removal of the aqueous phase, the Cu-loaded particles were re-suspended in water and a porous cage containing excess resin exchanger was added to each sample vial. After overnight mixing, the cage was retrieved and phases separated. Analysis of the aqueous phase determined the non-labile soluble copper released at the equilibrium pH; the ‘labile’ fraction value was found ...