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Adsorption Mechanisms of EDTA at the Water-Iron Oxide Interface: Implications for Dissolution

Noren, Katarina; Loring, John S.; Bargar, John R. and Persson, Per LU (2009) In Journal of Physical Chemistry C 113. p.7762-7771
Abstract
The interactions between chelating agents and metal oxide particles play important roles for the distribution and availability of metal ions in aquatic environments. In this work, the adsorption of ethylenediaminetetraacetate (EDTA) onto goethite (alpha-FeOOH) was studied as a function of pH, time, and background electrolyte concentration at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of infrared spectroscopy using the attenuated total reflectance sampling technique. The collective infrared spectroscopic results of this study show that two surface complexes consisting of HEDTA(3-) and H(2)EDTA(2-) predominate at the water-goethite interface within the pH range of 3-9. No direct... (More)
The interactions between chelating agents and metal oxide particles play important roles for the distribution and availability of metal ions in aquatic environments. In this work, the adsorption of ethylenediaminetetraacetate (EDTA) onto goethite (alpha-FeOOH) was studied as a function of pH, time, and background electrolyte concentration at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of infrared spectroscopy using the attenuated total reflectance sampling technique. The collective infrared spectroscopic results of this study show that two surface complexes consisting of HEDTA(3-) and H(2)EDTA(2-) predominate at the water-goethite interface within the pH range of 3-9. No direct interactions of these complexes with surface Fe(III) ions were detected; hence, most likely the surface complexes are stabilized at the interface by electrostatic and hydrogen-bonding forces. The formation of the EDTA surface complexes is fast (time scale of minutes), but a slower (time scale of hours to days) dissolution reaction also occurs. The dissolved iron in solution is in the form of the highly stable FeEDTA(-) solution complex, and the experimental evidence presented indicates that this complex can readsorb to the mineral surface. As dissolution proceeds, the concentration of FeEDTA- in the solution phase increases, and this in turn leads to a buildup of readsorbed FeEDTA- onto goethite. In the pH range of 4-7, this dissolution and readsorption process increases the total EDTA concentration at the surface. Under the experimental conditions in the present study, it is primarily the presence of uncomplexed EDTA in solution that drives the dissolution of goethite resulting in the subsequent readsorption of FeEDTA-, while the HEDTA(3-) and H(2)EDTA(2-) surface complexes are stable during this process. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry C
volume
113
pages
7762 - 7771
publisher
The American Chemical Society
external identifiers
  • scopus:67049167016
ISSN
1932-7447
DOI
10.1021/jp809190m
language
English
LU publication?
no
id
2862e972-016c-4d3c-a6ce-0964673df8c0 (old id 4332356)
date added to LUP
2014-03-04 09:46:48
date last changed
2017-09-10 03:43:30
@article{2862e972-016c-4d3c-a6ce-0964673df8c0,
  abstract     = {The interactions between chelating agents and metal oxide particles play important roles for the distribution and availability of metal ions in aquatic environments. In this work, the adsorption of ethylenediaminetetraacetate (EDTA) onto goethite (alpha-FeOOH) was studied as a function of pH, time, and background electrolyte concentration at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of infrared spectroscopy using the attenuated total reflectance sampling technique. The collective infrared spectroscopic results of this study show that two surface complexes consisting of HEDTA(3-) and H(2)EDTA(2-) predominate at the water-goethite interface within the pH range of 3-9. No direct interactions of these complexes with surface Fe(III) ions were detected; hence, most likely the surface complexes are stabilized at the interface by electrostatic and hydrogen-bonding forces. The formation of the EDTA surface complexes is fast (time scale of minutes), but a slower (time scale of hours to days) dissolution reaction also occurs. The dissolved iron in solution is in the form of the highly stable FeEDTA(-) solution complex, and the experimental evidence presented indicates that this complex can readsorb to the mineral surface. As dissolution proceeds, the concentration of FeEDTA- in the solution phase increases, and this in turn leads to a buildup of readsorbed FeEDTA- onto goethite. In the pH range of 4-7, this dissolution and readsorption process increases the total EDTA concentration at the surface. Under the experimental conditions in the present study, it is primarily the presence of uncomplexed EDTA in solution that drives the dissolution of goethite resulting in the subsequent readsorption of FeEDTA-, while the HEDTA(3-) and H(2)EDTA(2-) surface complexes are stable during this process.},
  author       = {Noren, Katarina and Loring, John S. and Bargar, John R. and Persson, Per},
  issn         = {1932-7447},
  language     = {eng},
  pages        = {7762--7771},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry C},
  title        = {Adsorption Mechanisms of EDTA at the Water-Iron Oxide Interface: Implications for Dissolution},
  url          = {http://dx.doi.org/10.1021/jp809190m},
  volume       = {113},
  year         = {2009},
}