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Competitive adsorption involving phosphate and benzenecarboxylic acids on goethite: Effects of molecular structures
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
2010 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, Vol. 343, no 1, 263-70 p.Article in journal (Other academic) Published
Abstract [en]

The competitive adsorption between phosphate and either one of seven benzenecarboxylates (benzoate, phthalate, trimellitate, trimesoate, hemimellitate, pyromellitate, and mellitate) on the surfaces of fine-particulate goethite (α-FeOOH) was investigated as a function of pH. The series of ligands contained molecules with an increasing number of functional groups as well as three structural isomers of the tricarboxylates. Thus, the effects of both the number of carboxylate groups and the relative positions of these groups on the competitive efficiency toward phosphate were probed in this study. Quantitative adsorption experiments in batch mode and infrared spectroscopy were collectively used to evaluate the competitive adsorption reactions. Under the conditions probed, mono- and dicarboxylates had no detectable effect on phosphate adsorption whereas the ligands containing three or more carboxylate groups were able to partially outcompete phosphate. However, the pH dependency and the extent of these competitive effects were strongly dependent on the structure and composition of the benzenecarboxylate. The collective results showed that it was the competition for hydrogen-bonding surface sites rather than inner sphere surface sites that primarily determined the outcome of the competitive adsorption experiments, and it was the ability of the organic ligand to act as hydrogen-bonding acceptor and/or donor in various parts of the pH range that also determined the competitive pH dependency. The importance of H-bonding for the competitive adsorption between phosphate and benzenecarboxylic acids suggested that H-bonding interactions contributed substantially to the stabilities of both the adsorbed benzenecarboxylates and the phosphate ions and that these interactions were structurally specific; i.e., they were sensitive to the locations and the directional properties of the H-acceptor and H-donor surface sites.

Place, publisher, year, edition, pages
Elsevier Inc , 2010. Vol. 343, no 1, 263-70 p.
Keyword [en]
Phosphate, Benzenecarboxylic acid, Competitive adsorption, Infrared spectroscopy
URN: urn:nbn:se:umu:diva-25720DOI: 10.1016/j.jcis.2009.11.040ISI: 000274548900037OAI: diva2:233404
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2010-02-08Bibliographically 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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