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Spectroscopic characterization of the coordination chemistry and hydrolysis of gallium(III) in the presence of aquatic organic matter

Hagvall, Kristoffer; Persson, Per LU and Karlsson, Torbjorn (2014) In Geochimica et Cosmochimica Acta 146. p.76-89
Abstract
Interactions between metals and natural organic matter (NOM) are of great environmental importance and one of the key factors influencing hydrolysis, solubility, and speciation of the metals. However, studying geochemically relevant metals like Al, Fe, and Cu is sometimes associated with analytical problems; for example Fe and Cu are both redox active. Gallium (Ga) is a non-redox active metal that usually occurs at very low concentrations in environmental samples and therefore a wide concentration range of metal(III)-NOM species can be explored by adding Ga(III) to such samples. This makes Ga(III) a good probe and analogue for other metal ions, in particular Al. In addition, due to the increased usage of Ga in society, a better... (More)
Interactions between metals and natural organic matter (NOM) are of great environmental importance and one of the key factors influencing hydrolysis, solubility, and speciation of the metals. However, studying geochemically relevant metals like Al, Fe, and Cu is sometimes associated with analytical problems; for example Fe and Cu are both redox active. Gallium (Ga) is a non-redox active metal that usually occurs at very low concentrations in environmental samples and therefore a wide concentration range of metal(III)-NOM species can be explored by adding Ga(III) to such samples. This makes Ga(III) a good probe and analogue for other metal ions, in particular Al. In addition, due to the increased usage of Ga in society, a better understanding of how Ga interacts with NOM is of importance but such studies are scarce. In this work, Ga(III) interactions with two different organic materials (Suwannee River natural organic matter and Suwannee River fulvic acid) were studied using infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopy in a large experimental range (101-84,076 mu g Ga g(-1) dry weight; pH 3-8). Our IR spectroscopic results showed that Ga(III) is bonded mainly to carboxylic functional groups and suggested that only a fraction of the total number of carboxylic sites in the samples was actively involved in the bonding. Modeling of the EXAFS data revealed that Ga(III) formed mononuclear chelate complexes with NOM that strongly suppressed the hydrolysis and polymerization of Ga(III). At low Ga(III) concentrations (1675-16,649 mu g g(-1)) organic complexes, consisting of 1-3 chelate ring structures, were the dominating species in the entire pH range while at higher concentrations (67,673-84,076 mu g g(-1), pH 3.0-7.0) we detected mixtures of mononuclear organic Ga(III) complexes, Ga(III) (hydr) oxide, and free Ga(III) (here defined as the hydrated Ga(III) ion and its soluble hydrolysis products). Moreover, the EXAFS results showed significantly higher contribution from second-shell C atoms (9-11) for the Ga(III)-organic complexes at the lowest concentration (101-125 mu g g(-1), pH 4.9-5.1), indicating formation of cage-like structures similar to Ga(III)-EDTA. Our combined results showed that Ga(III)-NOM interactions can be of importance for the solubility and speciation of Ga in environmental systems. Furthermore, the similarities between Ga(III) and previous Fe(III) results demonstrate that Ga(III) can be utilized as a probe for metal(III)-NOM interactions over an extended experimental range (e. g., pH and metal concentration) and thereby improve our knowledge about these interactions in general. (C) 2014 Elsevier Ltd. All rights reserved. (Less)
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Contribution to journal
publication status
published
subject
in
Geochimica et Cosmochimica Acta
volume
146
pages
76 - 89
publisher
Elsevier
external identifiers
  • wos:000344946000006
  • scopus:84910089495
ISSN
0016-7037
DOI
10.1016/j.gca.2014.10.006
project
MICCS - Molecular Interactions Controlling soil Carbon Sequestration
language
English
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yes
id
5bc1137d-db9e-4646-a05e-b081685d539e (old id 4982904)
date added to LUP
2015-01-27 10:47:40
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2017-07-30 03:21:41
@article{5bc1137d-db9e-4646-a05e-b081685d539e,
  abstract     = {Interactions between metals and natural organic matter (NOM) are of great environmental importance and one of the key factors influencing hydrolysis, solubility, and speciation of the metals. However, studying geochemically relevant metals like Al, Fe, and Cu is sometimes associated with analytical problems; for example Fe and Cu are both redox active. Gallium (Ga) is a non-redox active metal that usually occurs at very low concentrations in environmental samples and therefore a wide concentration range of metal(III)-NOM species can be explored by adding Ga(III) to such samples. This makes Ga(III) a good probe and analogue for other metal ions, in particular Al. In addition, due to the increased usage of Ga in society, a better understanding of how Ga interacts with NOM is of importance but such studies are scarce. In this work, Ga(III) interactions with two different organic materials (Suwannee River natural organic matter and Suwannee River fulvic acid) were studied using infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopy in a large experimental range (101-84,076 mu g Ga g(-1) dry weight; pH 3-8). Our IR spectroscopic results showed that Ga(III) is bonded mainly to carboxylic functional groups and suggested that only a fraction of the total number of carboxylic sites in the samples was actively involved in the bonding. Modeling of the EXAFS data revealed that Ga(III) formed mononuclear chelate complexes with NOM that strongly suppressed the hydrolysis and polymerization of Ga(III). At low Ga(III) concentrations (1675-16,649 mu g g(-1)) organic complexes, consisting of 1-3 chelate ring structures, were the dominating species in the entire pH range while at higher concentrations (67,673-84,076 mu g g(-1), pH 3.0-7.0) we detected mixtures of mononuclear organic Ga(III) complexes, Ga(III) (hydr) oxide, and free Ga(III) (here defined as the hydrated Ga(III) ion and its soluble hydrolysis products). Moreover, the EXAFS results showed significantly higher contribution from second-shell C atoms (9-11) for the Ga(III)-organic complexes at the lowest concentration (101-125 mu g g(-1), pH 4.9-5.1), indicating formation of cage-like structures similar to Ga(III)-EDTA. Our combined results showed that Ga(III)-NOM interactions can be of importance for the solubility and speciation of Ga in environmental systems. Furthermore, the similarities between Ga(III) and previous Fe(III) results demonstrate that Ga(III) can be utilized as a probe for metal(III)-NOM interactions over an extended experimental range (e. g., pH and metal concentration) and thereby improve our knowledge about these interactions in general. (C) 2014 Elsevier Ltd. All rights reserved.},
  author       = {Hagvall, Kristoffer and Persson, Per and Karlsson, Torbjorn},
  issn         = {0016-7037},
  language     = {eng},
  pages        = {76--89},
  publisher    = {Elsevier},
  series       = {Geochimica et Cosmochimica Acta},
  title        = {Spectroscopic characterization of the coordination chemistry and hydrolysis of gallium(III) in the presence of aquatic organic matter},
  url          = {http://dx.doi.org/10.1016/j.gca.2014.10.006},
  volume       = {146},
  year         = {2014},
}