Early diagenetic vivianite [Fe3(PO4)2 · 8H2O] in a contaminated freshwater sediment and insights into zinc uptake: A μ-EXAFS, μ-XANES and Raman study

Kevin G. Taylor, Karen A. Hudson-Edwards, Andrew J. Bennett, Vladimir Vishnyakov

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

The sediments in the Salford Quays, a heavily-modified urban water body, contain high levels of organic matter, Fe, Zn and nutrients as a result of past contaminant inputs. Vivianite [Fe3(PO4)2 · 8H2O] has been observed to have precipitated within these sediments during early diagenesis as a result of the release of Fe and P to porewaters. These mineral grains are small (<100 μm) and micron-scale analysis techniques (SEM, electron microprobe, μ-EXAFS, μ-XANES and Raman) have been applied in this study to obtain information upon the structure of this vivianite and the nature of Zn uptake in the mineral. Petrographic observations, and elemental, X-ray diffraction and Raman spectroscopic analysis confirms the presence of vivianite. EXAFS model fitting of the FeK-edge spectra for individual vivianite grains produces Fe-O and Fe-P co-ordination numbers and bond lengths consistent with previous structural studies of vivianite (4O atoms at 1.99-2.05 Å; 2P atoms at 3.17-3.25 Å). One analysed grain displays evidence of a significant Fe3+ component, which is interpreted to have resulted from oxidation during sample handling and/or analysis. EXAFS modelling of the Zn K-edge data, together with linear combination XANES fitting of model compounds, indicates that Zn may be incorporated into the crystal structure of vivianite (4O atoms at 1.97 Å; 2P atoms at 3.17 Å). Low levels of Zn sulphate or Zn-sorbed goethite are also indicated from linear combination XANES fitting and to a limited extent, the EXAFS fitting, the origin of which may either be an oxidation artifact or the inclusion of Zn sulphate into the vivianite grains during precipitation. This study confirms that early diagenetic vivianite may act as a sink for Zn, and potentially other contaminants (e.g. As) during its formation and, therefore, forms an important component of metal cycling in contaminated sediments and waters. Furthermore, for the case of Zn, the EXAFS fits for Zn phosphate suggest this uptake is structural and not via surface adsorption.

LanguageEnglish
Pages1623-1633
Number of pages11
JournalApplied Geochemistry
Volume23
Issue number6
Early online date9 Feb 2008
DOIs
Publication statusPublished - Jun 2008
Externally publishedYes

Fingerprint

vivianite
freshwater sediment
Zinc
Sediments
zinc
Atoms
Minerals
Impurities
Oxidation
Spectroscopic analysis
Bond length
Biological materials
Nutrients
Sulfates
Water
Phosphates
Crystal structure
Display devices
sediment
sulfate

Cite this

@article{b16c5e22714545b2b3ffd522f4532ab6,
title = "Early diagenetic vivianite [Fe3(PO4)2 · 8H2O] in a contaminated freshwater sediment and insights into zinc uptake: A μ-EXAFS, μ-XANES and Raman study",
abstract = "The sediments in the Salford Quays, a heavily-modified urban water body, contain high levels of organic matter, Fe, Zn and nutrients as a result of past contaminant inputs. Vivianite [Fe3(PO4)2 · 8H2O] has been observed to have precipitated within these sediments during early diagenesis as a result of the release of Fe and P to porewaters. These mineral grains are small (<100 μm) and micron-scale analysis techniques (SEM, electron microprobe, μ-EXAFS, μ-XANES and Raman) have been applied in this study to obtain information upon the structure of this vivianite and the nature of Zn uptake in the mineral. Petrographic observations, and elemental, X-ray diffraction and Raman spectroscopic analysis confirms the presence of vivianite. EXAFS model fitting of the FeK-edge spectra for individual vivianite grains produces Fe-O and Fe-P co-ordination numbers and bond lengths consistent with previous structural studies of vivianite (4O atoms at 1.99-2.05 {\AA}; 2P atoms at 3.17-3.25 {\AA}). One analysed grain displays evidence of a significant Fe3+ component, which is interpreted to have resulted from oxidation during sample handling and/or analysis. EXAFS modelling of the Zn K-edge data, together with linear combination XANES fitting of model compounds, indicates that Zn may be incorporated into the crystal structure of vivianite (4O atoms at 1.97 {\AA}; 2P atoms at 3.17 {\AA}). Low levels of Zn sulphate or Zn-sorbed goethite are also indicated from linear combination XANES fitting and to a limited extent, the EXAFS fitting, the origin of which may either be an oxidation artifact or the inclusion of Zn sulphate into the vivianite grains during precipitation. This study confirms that early diagenetic vivianite may act as a sink for Zn, and potentially other contaminants (e.g. As) during its formation and, therefore, forms an important component of metal cycling in contaminated sediments and waters. Furthermore, for the case of Zn, the EXAFS fits for Zn phosphate suggest this uptake is structural and not via surface adsorption.",
author = "Taylor, {Kevin G.} and Hudson-Edwards, {Karen A.} and Bennett, {Andrew J.} and Vladimir Vishnyakov",
year = "2008",
month = "6",
doi = "10.1016/j.apgeochem.2008.01.009",
language = "English",
volume = "23",
pages = "1623--1633",
journal = "Applied Geochemistry",
issn = "0883-2927",
publisher = "Elsevier Limited",
number = "6",

}

Early diagenetic vivianite [Fe3(PO4)2 · 8H2O] in a contaminated freshwater sediment and insights into zinc uptake : A μ-EXAFS, μ-XANES and Raman study. / Taylor, Kevin G.; Hudson-Edwards, Karen A.; Bennett, Andrew J.; Vishnyakov, Vladimir.

In: Applied Geochemistry, Vol. 23, No. 6, 06.2008, p. 1623-1633.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Early diagenetic vivianite [Fe3(PO4)2 · 8H2O] in a contaminated freshwater sediment and insights into zinc uptake

T2 - Applied Geochemistry

AU - Taylor, Kevin G.

AU - Hudson-Edwards, Karen A.

AU - Bennett, Andrew J.

AU - Vishnyakov, Vladimir

PY - 2008/6

Y1 - 2008/6

N2 - The sediments in the Salford Quays, a heavily-modified urban water body, contain high levels of organic matter, Fe, Zn and nutrients as a result of past contaminant inputs. Vivianite [Fe3(PO4)2 · 8H2O] has been observed to have precipitated within these sediments during early diagenesis as a result of the release of Fe and P to porewaters. These mineral grains are small (<100 μm) and micron-scale analysis techniques (SEM, electron microprobe, μ-EXAFS, μ-XANES and Raman) have been applied in this study to obtain information upon the structure of this vivianite and the nature of Zn uptake in the mineral. Petrographic observations, and elemental, X-ray diffraction and Raman spectroscopic analysis confirms the presence of vivianite. EXAFS model fitting of the FeK-edge spectra for individual vivianite grains produces Fe-O and Fe-P co-ordination numbers and bond lengths consistent with previous structural studies of vivianite (4O atoms at 1.99-2.05 Å; 2P atoms at 3.17-3.25 Å). One analysed grain displays evidence of a significant Fe3+ component, which is interpreted to have resulted from oxidation during sample handling and/or analysis. EXAFS modelling of the Zn K-edge data, together with linear combination XANES fitting of model compounds, indicates that Zn may be incorporated into the crystal structure of vivianite (4O atoms at 1.97 Å; 2P atoms at 3.17 Å). Low levels of Zn sulphate or Zn-sorbed goethite are also indicated from linear combination XANES fitting and to a limited extent, the EXAFS fitting, the origin of which may either be an oxidation artifact or the inclusion of Zn sulphate into the vivianite grains during precipitation. This study confirms that early diagenetic vivianite may act as a sink for Zn, and potentially other contaminants (e.g. As) during its formation and, therefore, forms an important component of metal cycling in contaminated sediments and waters. Furthermore, for the case of Zn, the EXAFS fits for Zn phosphate suggest this uptake is structural and not via surface adsorption.

AB - The sediments in the Salford Quays, a heavily-modified urban water body, contain high levels of organic matter, Fe, Zn and nutrients as a result of past contaminant inputs. Vivianite [Fe3(PO4)2 · 8H2O] has been observed to have precipitated within these sediments during early diagenesis as a result of the release of Fe and P to porewaters. These mineral grains are small (<100 μm) and micron-scale analysis techniques (SEM, electron microprobe, μ-EXAFS, μ-XANES and Raman) have been applied in this study to obtain information upon the structure of this vivianite and the nature of Zn uptake in the mineral. Petrographic observations, and elemental, X-ray diffraction and Raman spectroscopic analysis confirms the presence of vivianite. EXAFS model fitting of the FeK-edge spectra for individual vivianite grains produces Fe-O and Fe-P co-ordination numbers and bond lengths consistent with previous structural studies of vivianite (4O atoms at 1.99-2.05 Å; 2P atoms at 3.17-3.25 Å). One analysed grain displays evidence of a significant Fe3+ component, which is interpreted to have resulted from oxidation during sample handling and/or analysis. EXAFS modelling of the Zn K-edge data, together with linear combination XANES fitting of model compounds, indicates that Zn may be incorporated into the crystal structure of vivianite (4O atoms at 1.97 Å; 2P atoms at 3.17 Å). Low levels of Zn sulphate or Zn-sorbed goethite are also indicated from linear combination XANES fitting and to a limited extent, the EXAFS fitting, the origin of which may either be an oxidation artifact or the inclusion of Zn sulphate into the vivianite grains during precipitation. This study confirms that early diagenetic vivianite may act as a sink for Zn, and potentially other contaminants (e.g. As) during its formation and, therefore, forms an important component of metal cycling in contaminated sediments and waters. Furthermore, for the case of Zn, the EXAFS fits for Zn phosphate suggest this uptake is structural and not via surface adsorption.

UR - http://www.scopus.com/inward/record.url?scp=43949086515&partnerID=8YFLogxK

U2 - 10.1016/j.apgeochem.2008.01.009

DO - 10.1016/j.apgeochem.2008.01.009

M3 - Article

VL - 23

SP - 1623

EP - 1633

JO - Applied Geochemistry

JF - Applied Geochemistry

SN - 0883-2927

IS - 6

ER -