Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 60445
Title Proton binding to humic acids : electrostatic and intrinsic interactions
Author(s) Avena, M.J.; Koopal, L.K.; Riemsdijk, W.H. van
Source Journal of Colloid and Interface Science 217 (1999)1. - ISSN 0021-9797 - p. 37 - 48.
DOI http://dx.doi.org/10.1006/jcis.1999.6317
Department(s) Physical Chemistry and Colloid Science
Publication type Refereed Article in a scientific journal
Publication year 1999
Abstract The proton adsorption behavior of eight humic acids (HA) and a fulvic acid (FA) was studied as a function of pH and KNO3 concentration. The emphasis is on the comparison of the different humics with respect to their ion binding properties and on the comparison of two different models to describe the electrostatic interactions: the Donnan model and the impermeable sphere (IS) model. Viscosimetric data were used to estimate the hydrodynamic volumes and radii of the HA molecules. These data were incorporated in the electrostatic models and calculations could be carried out without any adjustable parameter. The Donnan model in combination with hydrodynamic volumes obtained by viscometry cannot adequately describe the electrostatic effects related to changes of the electrolyte concentration. This model leads to good prediction of the HA behavior if unrealistically large volumes are used for fulvics and unrealistically large volume-salt concentration dependencies are used for humics. The IS model can successfully reproduce experimental proton adsorption data with physically realistic radii. The good performance of the IS model and the poor performance of the Donnan model is directly related to the fact that the hydrodynamic volumes of the molecules are too small to allow for charge compensation within the molecular limits. The combination of viscometry with the IS model leads to a consistent description of the electrostatic in humics and to a consistent way of positioning the master curves. Therefore, the electrostatic potentials and the intrinsic affinity distributions of the different samples can be compared on an equal basis. The similarities in the intrinsic affinity distributions give faith for the possibility to develop a generic model to describe the ion binding to humics.
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