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Aqueous surface chemistry of Goethite: adsorption and desorption reactions involving phosphate and carboxylic acids
Umeå University, Faculty of Science and Technology, Chemistry.
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.
Identifiers
URN: urn:nbn:se:umu:diva-25727ISBN: 978-91-7264-774-9 (print)OAI: oai:DiVA.org:umu-25727DiVA: diva2:233417
Distributor:
Kemi, 90187, Umeå
Public defence
2009-09-25, KB3B1, KBC, Umeå University, 13:00 (English)
Opponent
Supervisors
Available from: 2009-09-03 Created: 2009-09-01 Last updated: 2009-09-03Bibliographically approved
List of papers
1. Molecular structures of citrate and tricarballylate adsorbed on α-FeOOH particles in aqueous suspensions
Open this publication in new window or tab >>Molecular structures of citrate and tricarballylate adsorbed on α-FeOOH particles in aqueous suspensions
2009 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 18, 10639-10647 p.Article in journal (Refereed) Published
Abstract [en]

In this work, the adsorption of citric (2-hydroxypropane-1,2,3-tricarboxylic acid) and tricarballylic (propane-1,2,3-tricarboxylic acid) acids onto α-FeOOH (goethite) in aqueous suspensions was studied as a function of pH and total ligand concentration in 0.1 M NaCl at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The adsorption experiments were carried out as a series of batch experiments, and a newly developed simultaneous infrared and potentiometric titration technique was used to collect in situ infrared spectra with high signal-to-noise ratios. The high quality of the infrared spectra allowed analysis by means of two-dimensional correlation spectroscopy formalism that aided the resolution of pH-dependent spectral features. This has enabled the detection of two previously unidentified citrate-goethite surface complexes: one protonated species at low pH, and one inner sphere complex prevailing at high pH and coordinated via a combination of hydroxyl and carboxylate groups. In addition, an inner sphere complex involving only carboxylate coordination predominating at low pH and an outer sphere complex existing in the circumneutral pH region were identified. The behavior of tricarballylate parallels that of citrate, except no inner sphere surface complex is formed at high pH values, which is in accordance with the lack of an α-hydroxyl group. The comparison between citrate and tricarballylate reinforces previous observations showing that inner sphere surface complexes of pure carboxylates at water-iron oxide interfaces are suppressed at high pH values, where outer sphere species are relatively more predominant. It also shows that significant amounts of inner sphere surface complexes of carboxylates only seem to form in the basic pH region when the ligands contain complementary functional groups, such as the hydroxyl or amine groups.

Place, publisher, year, edition, pages
American Chemical Society, 2009
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-25718 (URN)10.1021/la900852p (DOI)
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2017-12-13Bibliographically approved
2. Competitive adsorption between phosphate and carboxylic acids: quantitative effects and molecular mechanisms
Open this publication in new window or tab >>Competitive adsorption between phosphate and carboxylic acids: quantitative effects and molecular mechanisms
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
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-25719 (URN)10.1111/j.1365-2389.2009.01171.x (DOI)
Note
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: 2017-12-13Bibliographically approved
3. Competitive adsorption involving phosphate and benzenecarboxylic acids on goethite: Effects of molecular structures
Open this publication in new window or tab >>Competitive adsorption involving phosphate and benzenecarboxylic acids on goethite: Effects of molecular structures
2010 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, 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
Keyword
Phosphate, Benzenecarboxylic acid, Competitive adsorption, Infrared spectroscopy
Identifiers
urn:nbn:se:umu:diva-25720 (URN)10.1016/j.jcis.2009.11.040 (DOI)000274548900037 ()
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2017-12-13Bibliographically approved
4. Desorption of benzenecarboxylates from the water-goethite interface
Open this publication in new window or tab >>Desorption of benzenecarboxylates from the water-goethite interface
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:umu:diva-25722 (URN)
Available from: 2009-09-01 Created: 2009-09-01 Last updated: 2010-01-14Bibliographically approved
5. Dissolution, adsorption and phase transformation in the fluorapatite–goethite system
Open this publication in new window or tab >>Dissolution, adsorption and phase transformation in the fluorapatite–goethite system
2007 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 22, no 9, 2016-2028 p.Article in journal (Refereed) Published
Abstract [en]

An aqueous system containing fluorapatite (Ca5(PO4)3F), (FAP) and varying amounts of goethite (α-FeOOH) has been investigated. Batch experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to monitor the dissolution products of FAP, as well as the adsorption, and phase transformation of phosphate at the goethite surface over a period of 129 days. The results show that the presence of goethite increases dissolution of FAP, mainly due to the high affinity of phosphate for the goethite surface: Besides monitoring the pH changes associated with this reaction, the concentrations of Ca2+ and fluoride were determined. Furthermore, the amount of phosphate adsorbed was quantified from ATR-FTIR spectra. In addition to adsorbed phosphate, phase transformations of goethite into a Fe phosphate phase (FePO4(s)) are seen in the samples with relatively high phosphate to goethite ratios (excess phosphate to available surface sites) equilibrated for 15–129 days.

An equilibrium model that takes into account (i) FAP dissolution, (ii) solution complexation, (iii) surface complexation of phosphate species onto goethite and (iv) possible phase transformation Ca5(PO4)3F–CaF2 and FeOOH–FePO4 was designed. This model was found to be in very good agreement with experimental observations and could thus be used to give qualitative and quantitative information about goethite promoted dissolution of FAP under other pH conditions than those studied in the present work.

Place, publisher, year, edition, pages
Elsevier, ScienceDirect, 2007
Identifiers
urn:nbn:se:umu:diva-16233 (URN)doi:10.1016/j.apgeochem.2007.05.001 (DOI)
Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2017-12-14Bibliographically approved

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