Voltammetric Analysis of Heterogeneity in Metal Ion Binding by Humics

• Published in: Environmental science & technology Vol. 35; no. 6; pp. 1097 - 1102
• Main Authors: Berbel, Francisco, Díaz-Cruz, José Manuel, Ariño, Cristina, Esteban, Miquel, Mas, Francesc, Garcés, Josep Lluís, Puy, Jaume
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.03.2001
• Subjects: Applied sciences; Benzopyrans - chemistry; Biological and physicochemical phenomena; Biological and physicochemical properties of pollutants. Interaction in the soil; Cadmium - chemistry; Chemical reactions; Copper - chemistry; Earth sciences; Earth, ocean, space; Electrochemistry; Engineering and environment geology. Geothermics; Environment; Environmental Monitoring - methods; Environmental Pollutants - analysis; Exact sciences and technology; Ions; Lead - chemistry; Ligands; Metals; Natural water pollution; Pollution; Pollution, environment geology; Protons; Soil and sediments pollution; Voltammetry; Water treatment and pollution; Cadmium; Complexation; Organic matter; Pollutant behavior; Geochemistry; Voltammetry; Binding site; Soil pollution; Heavy metal; Competitive fixation; Pulse polarography; Lead; Water pollution; Fulvic acid; Copper; Acid base titration
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es000111y

The complexation of Cd, Pb, and Cu by fulvic acids at a fixed pH and ionic strength is studied by means of different voltammetric techniques at any metal-to-ligand ratio. When using Reverse Pulse Polarography (RPP) the complex species are electrochemically labile and not subject to significant electrodic adsorption. RPP titrations of fulvic acid with metal ions are interpreted on the basis of a recently proposed analytical expression for limiting currents valid for fully labile heterogeneous complexation. The voltammetric data are transformed into the corresponding binding curve, i.e., the fraction of occupied sites vs free metal concentration. Finally, the competition between metal ions and protons in their interaction with the fulvic binding sites as well as the concomitant polyelectrolytic effects are analyzed in terms of the NICCA-Donnan model. The results show that voltammetric techniques can be applied to the studies of heterogeneous complex systems in a broad range of metal-to-ligand ratios.