Carbonate adsorption on goethite in competition with phosphate
Rasoul Rahnemaie1, Tjisse Hiemstra, Willem H van Riemsdijk
1Department of Soil Quality, Wageningen University, PO Box 47, NL 6700 AA Wageningen, The Netherlands.
Journal of Colloid and Interface Science
|September 11, 2007
Summary
Phosphate and carbonate compete for binding sites on goethite, a common soil mineral. Carbonate primarily forms a strong bidentate inner-sphere complex, influencing phosphate adsorption and showing a competitive interaction.
Area of Science:
- Geochemistry
- Environmental Science
- Surface Chemistry
Background:
- Carbonate and phosphate are ubiquitous anions in natural systems like soils and sediments.
- Understanding their competitive interactions on mineral surfaces is crucial for environmental processes.
Purpose of the Study:
- To quantitatively study the competitive adsorption of carbonate and phosphate on goethite.
- To model these interactions using the charge distribution (CD) model and molecular orbital calculations.
Main Methods:
- Experimental study of anion adsorption on goethite in binary and single-ion systems.
- Charge distribution (CD) modeling.
- Molecular orbital calculations using density functional theory (MO/DFT) to determine surface complex geometries.
Main Results:
- Phosphate and carbonate exhibit competitive adsorption on goethite.
- Carbonate adsorption is dominated by a bidentate inner-sphere complex, (FeO)2CO.
- The CD model accurately describes experimental data, predicting both competitive effects and single-ion adsorption.
Conclusions:
- The study elucidates the competitive binding mechanisms of carbonate and phosphate on goethite.
- A bidentate inner-sphere complex is the primary mode of carbonate adsorption.
- The findings contribute to a better understanding of anion behavior in environmental systems.
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