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Competitive adsorption between phosphate and carboxylic acids: quantitative effects and molecular mechanisms
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2009 (English)In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 60, no 6, 982-993 p.Article in journal (Refereed) Published
Abstract [en]

The competitive adsorption at the water-goethite interface between phosphate and a carboxylic acid, either oxalate, citrate, 1,2,3,4-butanetetracarboxylic acid (BTCA), mellitate or Suwannee River Standard Fulvic Acid 1S101F (FA), was investigated over a wide pH range (3–9) by means of batch experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The quantitative results from the competitive adsorption measurements show that the efficiency of the organic acids in competing with phosphate was in the order oxalate < citrate < BTCA ≅ FA < mellitate. Oxalate showed no detectable effect, whereas the effect in the mellitate system was strong, and the aggregative results indicate that an increasing number of carboxylic groups favours competitive ability towards phosphate. The infrared spectroscopic results show conclusively that competition for goethite surface sites between carboxylic acids and phosphate is not a ligand-exchange reaction between inner-sphere surface complexes. Instead, ligands capable of multiple H-bonding interactions are required to out-compete and desorb surface complexes of phosphate. The fact that partially protonated organic acids are the most efficient emphasizes the importance of both H-accepting carboxylate groups and H-donating carboxylic acid groups for the competitive effect.

Place, publisher, year, edition, pages
Wiley InterScience , 2009. Vol. 60, no 6, 982-993 p.
National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-25719DOI: 10.1111/j.1365-2389.2009.01171.xOAI: diva2:233402
Published Online 26 Aug 2009 under Early View (Articles online in advance of print)Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2012-08-10Bibliographically approved
In thesis
1. Aqueous surface chemistry of Goethite: adsorption and desorption reactions involving phosphate and carboxylic acids
Open this publication in new window or tab >>Aqueous surface chemistry of Goethite: adsorption and desorption reactions involving phosphate and carboxylic acids
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phosphorus is an essential element for all known forms of life. In the form of phosphate, this nutrient is retained in soils and sediments by sorption on mineral particles, clays and other soil constituents. In addition, phosphate precipitates with metal ions to form a range of phosphate containing minerals, and only a minor part of phosphate is found dissolved in soil solution. One way of releasing sorbed phosphate is through ligand exchange reactions with for example carboxylic acids. This thesis summarizes five papers and focuses on the interactions of phosphate and carboxylates at the water-goethite interface. Quantitative adsorption data and spectroscopic evaluations of the surface complexation were used collectively to gain a better understanding of these processes. In agreement with previous studies, it was found that the number of carboxylic groups is important to the competitive ability of the organic acids towards phosphate. However, it was also shown that the positions of the functional groups are highly relevant to this ability. Furthermore, partially protonated species were – because of hydrogen bond interactions - shown to be more competitive than fully deprotonated equivalents. Another central finding in this work is that competitive interactions do not necessarily involve ligand-exchange reactions between inner sphere surface complexes.  To study the lability of the complexes, desorption experiments were performed. Among the benzenecarboxylates, the order of increased lability matched that of the decreased ability to compete with phosphate for surface sites on the goethite. Also shown in this thesis is the ability of goethite to increase the dissolution of fluorapatite mainly through the high affinity of phosphate ions for the goethite surface.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2009. 39 p.
urn:nbn:se:umu:diva-25727 (URN)978-91-7264-774-9 (ISBN)
Kemi, 90187, Umeå
Public defence
2009-09-25, KB3B1, KBC, Umeå University, 13:00 (English)
Available from: 2009-09-03 Created: 2009-09-01 Last updated: 2009-09-03Bibliographically approved

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