Application of the NICADonnan model for proton, copper and uranyl binding to humic acid
Saito, T. ; Nagasaki, S. ; Tanaka, S. ; Koopal, L.K. - \ 2004
Radiochimica Acta 92 (2004)9-11. - ISSN 0033-8230 - p. 567 - 574.
metal-ion binding - fulvic-acids - humate interactions - substances - complexation - adsorption - parameters - heterogeneity - uranium(vi) - goethite
Humic acids are natural organic materials that play an important role in the migration of heavy metal and actinide ions in aquatic and soil systems. In the present study, the binding of protons, copper ions and uranyl ions to the purified Aldrich humic acid (PAHA) is investigated and the results are modeled with the Non-Ideal Competitive Adsorption (NICA) model extended with electrostatic interactions according to the Donnan model (NICA-Donnan model). The NICA part of the model enables one to describe the competitive ion binding to a heterogeneous substrate taking into account a different stoichiometry per ion. The NICA-Donnan model can describe the binding of the ions to PAHA in large concentration ranges (3
Adsorption of humic acid on goethite: Isotherms, charge adjustments and potential profiles
Saito, T. ; Koopal, L.K. ; Riemsdijk, W.H. van; Nagasaki, S. ; Tanaka, S. - \ 2004
Langmuir 20 (2004)3. - ISSN 0743-7463 - p. 689 - 700.
natural organic-matter - oxide-water interface - metal-ion binding - donnan model parameters - fulvic-acid - iron-oxide - polyelectrolyte adsorption - weak polyelectrolytes - humate interactions - surface ionization
The adsorption of natural organic matter (NOM) on mineral (hydr)oxide plays an important role in the evaluation of the speciation of toxic metal ions in the environment. Because both NOM and mineral oxide have variable charges that adjust upon adsorption, a good understanding of proton binding is required before the binding of metal ions can be understood. In this study, the adsorption of purified Aldrich humic acid (PAHA) on goethite was examined as a function of the environmental conditions (pH, salt concentration, and free concentration of PAHA) together with the proton adsorption to PAHA, goethite, and their mixtures. The induced charges on both components were separated on the basis of the difference between the charge/pH curves of the mixture and those of the single components. The electrostatic potential profile across the adsorbed layer was obtained as a numerical solution of the Poisson-Boltzmann equation using the charge density of the adsorbed PAHA and the goethite surface. From the quantitative evaluation of the induced charge on both components, it is revealed that the degree of the charge adjustment is related to the electrostatic affinity between the PAHA segments and the goethite surface, the electrostatic repulsion between the PAHA segments, and the electrostatic shielding by salt ions. Considering the charge distribution of the adsorbed PAHA at the goethite surface, it is concluded that the change of the charge adjustment is sensitive to that of the conformation of the adsorbed PAHA. From the detailed inspection of the assumptions made and the comparison with the reported theoretical calculations, the obtained potential profiles are considered to broadly reflect the true potential profiles. Because a charge adjustment is not frequently considered in detail in relation to the NOM adsorption on metal (hydr)oxides, the obtained results can form the basis for the further development of modeling of the adsorption of NOM on (hydr)oxide surfaces.
Generic NICA-Donnan model parameters for metal-ion binding by humic substances
Milne, C.J. ; Kinniburgh, D.G. ; Riemsdijk, W.H. van; Tipping, E. - \ 2003
Environmental Science and Technology 37 (2003)5. - ISSN 0013-936X - p. 958 - 971.
conditional stability-constants - fulvic-acid complexes - selective electrode - proton binding - humate interactions - cadmium-binding - organic-matter - cation binding - cu(ii) ion - aluminum
A total of 171 datasets of literature and experimental data for metal-ion binding by fulvic and humic acids have been digitized and re-analyzed using the NICA-Donnan model. Generic parameter values have been derived that can be used for modeling in the absence of specific metal-ion binding measurements. These values complement the previously derived generic descriptions of proton binding. For ions where the ranges of pH, concentration, and ionic strength conditions are well covered by the available data, the generic parameters successfully describe the metal-ion binding behavior across a very wide range of conditions and for different humic and fulvic acids. Where published data for other metal ions are too sparse to constrain the model well, generic parameters have been estimated by interpolating trends observable in the parameter values of the well-defined data. Recommended generic NICA-Donnan model parameters are provided for 23 metal ions (Al, Am, Ba, Ca, Cd, Cm, Co, CrIII, Cu, Dy, Eu, FeII, FeIII, Hg, Mg, Mn, Ni, Pb, Sr, ThIV, UVIO2, VIIIO, and Zn) for both fulvic and humic acids. These parameters probably represent the best NICA-Donnan description of metal-ion binding that can be achieved using existing data