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Impact of iron-organic matter complexes on aqueous phosphate concentrations

Sundman, Anneli; Karlsson, Torbjörn; Sjöberg, Staffan and Persson, Per LU (2016) In Chemical Geology 426. p.109-117
Abstract

The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may have a strong effect on the bioavailability of P. At the same time Fe speciation in natural oxic environments is known to be affected by the presence of organic matter (OM), pH and total Fe concentrations, thus these parameters should also influence the Fe-P interactions. The main objective of the present work was to study how OM affected the distribution of P(V) in the presence of Fe(III) and to address the questions if and by what mechanism(s) OM influenced the concentration of aqueous phosphate. This was accomplished by investigating the ternary P(V)-Fe(III)-OM system over a wide range of chemical conditions; [Fe]tot =... (More)

The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may have a strong effect on the bioavailability of P. At the same time Fe speciation in natural oxic environments is known to be affected by the presence of organic matter (OM), pH and total Fe concentrations, thus these parameters should also influence the Fe-P interactions. The main objective of the present work was to study how OM affected the distribution of P(V) in the presence of Fe(III) and to address the questions if and by what mechanism(s) OM influenced the concentration of aqueous phosphate. This was accomplished by investigating the ternary P(V)-Fe(III)-OM system over a wide range of chemical conditions; [Fe]tot = 5000-50,000 μg g-1, Fe/P = 0.5-2.0 at pH 2.9-7. Iron speciation was probed via Fe K-edge X-ray absorption spectroscopy, P speciation and concentrations were analyzed via infrared spectroscopy, and chemical equilibrium modeling was conducted to simulate the distribution of chemical species of the system. The collective results showed that the dominating species were Fe(III)-OM complexes and ferric phosphate (FePO4(s)). At low concentrations, the Fe(III)-OM complexes suppressed the formation of FePO4(s), which resulted in elevated aqueous phosphate concentrations. At high concentrations, FePO4(s) was formed and co-existed with Fe(III)-OM complexes; ternary P(V)-Fe(III)-OM complexes were not detected under any experimental condition. The collective spectroscopic and equilibrium modeling results offer a mechanistic and thermodynamic consistent explanation to why OM contributes to elevated concentrations of soluble P and thereby to increased bioavailability of P in soils and waters.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Iron, Organic matter, Phosphate, X-ray absorption spectroscopy
in
Chemical Geology
volume
426
pages
9 pages
publisher
Elsevier
external identifiers
  • scopus:84958248292
  • wos:000371214700010
ISSN
0009-2541
DOI
10.1016/j.chemgeo.2016.02.008
language
English
LU publication?
yes
id
77558811-6df9-40e6-99e5-352421bb5233
date added to LUP
2016-05-10 08:10:59
date last changed
2017-09-24 04:57:15
@article{77558811-6df9-40e6-99e5-352421bb5233,
  abstract     = {<p>The close linkage between iron (Fe) and phosphorus (P) suggests that changes in Fe speciation may have a strong effect on the bioavailability of P. At the same time Fe speciation in natural oxic environments is known to be affected by the presence of organic matter (OM), pH and total Fe concentrations, thus these parameters should also influence the Fe-P interactions. The main objective of the present work was to study how OM affected the distribution of P(V) in the presence of Fe(III) and to address the questions if and by what mechanism(s) OM influenced the concentration of aqueous phosphate. This was accomplished by investigating the ternary P(V)-Fe(III)-OM system over a wide range of chemical conditions; [Fe]<sub>tot</sub> = 5000-50,000 μg g<sup>-1</sup>, Fe/P = 0.5-2.0 at pH 2.9-7. Iron speciation was probed via Fe K-edge X-ray absorption spectroscopy, P speciation and concentrations were analyzed via infrared spectroscopy, and chemical equilibrium modeling was conducted to simulate the distribution of chemical species of the system. The collective results showed that the dominating species were Fe(III)-OM complexes and ferric phosphate (FePO<sub>4</sub>(s)). At low concentrations, the Fe(III)-OM complexes suppressed the formation of FePO<sub>4</sub>(s), which resulted in elevated aqueous phosphate concentrations. At high concentrations, FePO<sub>4</sub>(s) was formed and co-existed with Fe(III)-OM complexes; ternary P(V)-Fe(III)-OM complexes were not detected under any experimental condition. The collective spectroscopic and equilibrium modeling results offer a mechanistic and thermodynamic consistent explanation to why OM contributes to elevated concentrations of soluble P and thereby to increased bioavailability of P in soils and waters.</p>},
  author       = {Sundman, Anneli and Karlsson, Torbjörn and Sjöberg, Staffan and Persson, Per},
  issn         = {0009-2541},
  keyword      = {Iron,Organic matter,Phosphate,X-ray absorption spectroscopy},
  language     = {eng},
  month        = {05},
  pages        = {109--117},
  publisher    = {Elsevier},
  series       = {Chemical Geology},
  title        = {Impact of iron-organic matter complexes on aqueous phosphate concentrations},
  url          = {http://dx.doi.org/10.1016/j.chemgeo.2016.02.008},
  volume       = {426},
  year         = {2016},
}