An Analytical Isotherm Equation (CONICA) for Nonideal Mono- and Bidentate Competitive Ion Adsorption to Heterogeneous Surfaces
✍ Scribed by Willem H. van Riemsduk; Johannes C.M. de Wit; Sipko L.J. Mous; Luuk K. Koopal; David G. Kinniburgh
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 316 KB
- Volume
- 183
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
dominantly of a ''carboxylic' ' and ''phenolic'' nature (1), Analytical isotherm equations for the competitive binding of but as with the oxides differences in the chemical environprotons and other cations to heterogeneous surfaces have been ment of the two types of groups lead to a wide range of derived. These extend our earlier nonideal competitive adsorption affinity constants, i.e., a large chemical heterogeneity. This (NICA) equation by considering bidentate as well as monodentate is reflected in the distribution of proton affinities of these binding of ions. The protonation of these bidentate sites occurs in materials (2). For humic acids, the proton affinity distributwo COnsecutive steps. The CONICA model equations separate tion shows two broad peaks with approximately the same the apparent heterogeneity into a generic heterogeneity characternumber of sites per peak. Calculation of the local electroistic of all of the surface sites and an ion-specific contribution static potential (3-5) as a function of pH shows that the characteristic of each type of ion. The CONICA model was combined with a simple Donnan model to account for electrostatic electrostatic effects are much less pronounced than for metal effects and was fitted both to proton binding at various ionic oxides (6) but are nevertheless significant.
strengths and to the pH-dependent binding of Cu (pH 4, 6, and
A characteristic of metal ion binding to metal oxides and 8) to a purified peat humic acid. Model fits were good. The meahumic and fulvic acids is that at constant pH and salt concensured H / /Cu 2/ exchange ratio is significantly greater than one tration, a Freundlich (log-log) plot shows that there is a for the whole pH range, which indicates the importance of the slope of less than one over a fairly wide range of free metal bidentate binding mechanism for copper.