Fluoride adsorption on goethite in relation to different types of surface sites
Metal (hydr)oxides have different types of surface groups. Fluoride ions have been used as a probe to assess the number of surface sites. The authors have studied the F{sup {minus}} adsorption on goethite by measuring the F{sup {minus}} and H{sup +} interaction and F{sup {minus}} adsorption isotherms. Fluoride ions exchange against singly coordinated surface hydroxyls at low F{sup {minus}} concentrations. At higher concentrations also the doubly coordinated OH groups are involved. The replacement of a surface OH{sup {minus}} by F{sup {minus}} suggests that all F charge ({minus}1) is located at the surface in contrast to oxyanions which have a charge distribution in the interface due to the binding structure in which the anion only partially coordinates with the surface. Analysis of their F{sup {minus}} data with the CD-MUSIC approach shows that the formation of the fluoride surface complex is accompanied by a redistribution of charge. This is supposed to be due to a net switch in the H bonding as a result of the change of the type of surface complex from donating (FeOH, FeOH{sub 2}) to proton accepting (FeF). The modeled redistribution of charge is approximately equivalent with the change of a donating H bond into an accepting H bond. At high F{sup {minus}} concentrations precipitation of F{sup {minus}}, as for instance FeF{sub 3}(s), may occur. The rate of formation is catalyzed by the presence of high electrolyte concentrations.
- Research Organization:
- Wageningen Univ. (NL)
- OSTI ID:
- 20075581
- Journal Information:
- Journal of Colloid and Interface Science, Vol. 225, Issue 1; Other Information: PBD: 1 May 2000; ISSN 0021-9797
- Country of Publication:
- United States
- Language:
- English
Similar Records
Capturing the variable reactivity of goethites in surface complexation modeling by correlating model parameters with specific surface area
The influence of metal ions on the adsorption of phosphonates onto goethite