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Inorganic and organic P retention by coprecipitation during ferrous iron oxidation

Santoro, Veronica LU ; Martin, Maria; Persson, Per LU ; Lerda, Cristina; Said-Pullicino, Daniel; Magnacca, Giuliana and Celi, Luisella (2019) In Geoderma 348. p.168-180
Abstract

Phosphorous (P) cycling is often closely coupled to iron (Fe), particularly following mineral weathering or in hydromorphic soils where Fe redox reactions can control the equilibrium between P retention and release. While surface adsorption of P on Fe (hydr)oxides is a well-known and widely studied process, less attention has been devoted to the understanding of P (especially organic P) coprecipitation following Fe(II) oxidative precipitation. In this work we synthesized and followed the kinetics of a series of Fe-P systems with increasing P/Fe ratio, prepared by either surface adsorption on ferrihydrite (Fh) or oxidative coprecipitation of Fe(II) with inorganic phosphate (Pi), inositol hexaphosphate (myoInsP6) or phosphatidylcholine... (More)

Phosphorous (P) cycling is often closely coupled to iron (Fe), particularly following mineral weathering or in hydromorphic soils where Fe redox reactions can control the equilibrium between P retention and release. While surface adsorption of P on Fe (hydr)oxides is a well-known and widely studied process, less attention has been devoted to the understanding of P (especially organic P) coprecipitation following Fe(II) oxidative precipitation. In this work we synthesized and followed the kinetics of a series of Fe-P systems with increasing P/Fe ratio, prepared by either surface adsorption on ferrihydrite (Fh) or oxidative coprecipitation of Fe(II) with inorganic phosphate (Pi), inositol hexaphosphate (myoInsP6) or phosphatidylcholine (PC). The obtained materials were characterized for P and Fe contents, specific surface area (SSA), porosity and surface charge. XRD, TEM, XPS and IR techniques were used to investigate their properties. P retention by coprecipitation was generally greater with respect to adsorption, especially at the highest initial P/Fe ratio. Inorganic phosphate caused interference and poisoning of the crystallization process, slowing down Fe(II) oxidation and precipitation rates at low P/Fe ratios, with the formation of nanometric particles and phosphate concentrated on their surface. With increasing P loadings, more aggregated particles with a lower SSA and greater porosity were obtained. Aside from precipitation, the retention mechanisms also involved adsorption and/or inclusion of Pi within the particles. myoInsP6, on the other hand, contributed to accelerating the precipitation of Fe, leading to coprecipitates bearing the organic P compound within the structure, and was retained by precipitation and adsorption mechanisms. Conversely, irrespective of the P/Fe ratio, PC did not influence the rate of Fe(II) oxidation and precipitation due to its hydrophobic character. The prevailing mechanism involved in its retention during coprecipitation was physical retention on the surface, leading to a drastic decrease of SSA and pore volume. Coprecipitation is thus a complex process, involving several mechanisms as a function of the P species and initial P/Fe ratio, and further contributing to the stabilization and selective accumulation of myoInsP6 in soil with respect to other organic P forms.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Ferrihydrite, Inositol hexaphosphate, Phosphate, Phosphatidylcholine, Surface adsorption, Surface properties
in
Geoderma
volume
348
pages
13 pages
publisher
Elsevier
external identifiers
  • scopus:85064929070
ISSN
0016-7061
DOI
10.1016/j.geoderma.2019.04.004
language
English
LU publication?
yes
id
fbead29e-80e4-45ef-9e43-ddc833545715
date added to LUP
2019-05-13 09:29:38
date last changed
2019-06-04 03:57:56
@article{fbead29e-80e4-45ef-9e43-ddc833545715,
  abstract     = {<p>Phosphorous (P) cycling is often closely coupled to iron (Fe), particularly following mineral weathering or in hydromorphic soils where Fe redox reactions can control the equilibrium between P retention and release. While surface adsorption of P on Fe (hydr)oxides is a well-known and widely studied process, less attention has been devoted to the understanding of P (especially organic P) coprecipitation following Fe(II) oxidative precipitation. In this work we synthesized and followed the kinetics of a series of Fe-P systems with increasing P/Fe ratio, prepared by either surface adsorption on ferrihydrite (Fh) or oxidative coprecipitation of Fe(II) with inorganic phosphate (Pi), inositol hexaphosphate (myoInsP6) or phosphatidylcholine (PC). The obtained materials were characterized for P and Fe contents, specific surface area (SSA), porosity and surface charge. XRD, TEM, XPS and IR techniques were used to investigate their properties. P retention by coprecipitation was generally greater with respect to adsorption, especially at the highest initial P/Fe ratio. Inorganic phosphate caused interference and poisoning of the crystallization process, slowing down Fe(II) oxidation and precipitation rates at low P/Fe ratios, with the formation of nanometric particles and phosphate concentrated on their surface. With increasing P loadings, more aggregated particles with a lower SSA and greater porosity were obtained. Aside from precipitation, the retention mechanisms also involved adsorption and/or inclusion of Pi within the particles. myoInsP6, on the other hand, contributed to accelerating the precipitation of Fe, leading to coprecipitates bearing the organic P compound within the structure, and was retained by precipitation and adsorption mechanisms. Conversely, irrespective of the P/Fe ratio, PC did not influence the rate of Fe(II) oxidation and precipitation due to its hydrophobic character. The prevailing mechanism involved in its retention during coprecipitation was physical retention on the surface, leading to a drastic decrease of SSA and pore volume. Coprecipitation is thus a complex process, involving several mechanisms as a function of the P species and initial P/Fe ratio, and further contributing to the stabilization and selective accumulation of myoInsP6 in soil with respect to other organic P forms.</p>},
  author       = {Santoro, Veronica and Martin, Maria and Persson, Per and Lerda, Cristina and Said-Pullicino, Daniel and Magnacca, Giuliana and Celi, Luisella},
  issn         = {0016-7061},
  keyword      = {Ferrihydrite,Inositol hexaphosphate,Phosphate,Phosphatidylcholine,Surface adsorption,Surface properties},
  language     = {eng},
  pages        = {168--180},
  publisher    = {Elsevier},
  series       = {Geoderma},
  title        = {Inorganic and organic P retention by coprecipitation during ferrous iron oxidation},
  url          = {http://dx.doi.org/10.1016/j.geoderma.2019.04.004},
  volume       = {348},
  year         = {2019},
}