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Title: Competition effects in cation binding to humic acid: Conditional affinity spectra for fixed total metal concentration conditions
Author: David, Calin
Mongin, Sadrine
Rey-Castro, Carlos
Galceran, Josep
Companys, Encarnació
Garcés, Josep Lluís
Salvador, José
Puy, Jaume
Cecilia, Joan
Lodeiro, Pablo
Mas i Pujadas, Francesc
Keywords: Macromolècules
Àcid húmic
Equilibri àcid-base
Humic acid
Acid-base equilibrium
Issue Date: 2010
Publisher: Elsevier Ltd
Abstract: Information on the Pb and Cd binding to a purified Aldrich Humic Acid (HA) is obtained from the influence of different fixed total metal concentrations on the acid- base titrations of this ligand. NICA (Non-Ideal Competitive Adsorption) isotherm has been used for a global quantitative description of the binding, which has then been interpreted by plotting the Conditional Affinity Spectra of the H+ binding at fixed total metal concentrations (CAScTM). This new physicochemical tool, here introduced, allows the interpretation of binding results in terms of distributions of proton binding energies. A large increase in the acidity of the phenolic sites as the total metal concentration increases, especially in presence of Pb, is revealed from the shift of the CAScTM towards lower affinities. The variance of the CAScTM distribution, which can be used as a direct measure of the heterogeneity, also shows a significant dependence on the total metal concentration. A discussion of the factors that influence the heterogeneity of the HA under the conditions of each experiment is provided, so that the smoothed pattern exhibited by the titration curves can be justified.
Note: Versió postprint del document publicat a:
It is part of: Geochimica et Cosmochimica Acta, 2010, vol. 74, num. 18, p. 5216-5227
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ISSN: 0016-7037
Appears in Collections:Articles publicats en revistes (Ciència dels Materials i Química Física)

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