Contribution of metal‐ion complex formation with organic substances to the acidity of water extracts of polluted soils

Abstract

The formation of complexes of copper ions with organic substances in soil water extracts and the development of acid–base properties of the extracts were examined. Potentiometric titration of water extracts from several soils with copper nitrate solution with a consecutive determination of the activity of protons and copper ions in the extracts was performed. This demonstrated the existence of a functional relationship between the complexing of copper ions with organic substances and the acid–base properties of the water extracts. The parameters of the interrelated processes of formation and dissociation of metal–organic complexes and the protonation‐deprotonation of organic acids, the ligands of which participate in the complexing reactions, were determined. It was found that the formation of the complexes is accompanied by the acidification of the solution from the acid hydrolysis of the copper ions and the displacement of protons from the functional groups of organic acids. The protons released in the course of complexing reactions affected these reactions. Under their impact, the stability of the copper–organic complexes decreased; finally, the formation of the complexes and the release of protons stopped, and the pH of the extracts reached an equilibrium level.

Soil Interfaces in a Changing World

“…The random sequential adsorption (RSA) model of capture of particles gave a good description of the influence of Cu 2+ and pH on the transport of HAs. The complexes of copper ions with organic substances can contribute to acidity of water extracts of polluted soils as described by Motuzova et al (2012). The protons released during complexation reactions with the functional groups of organic acids and acid hydrolysis of the copper ions affected the stability of the copper–organic complexes.…”