TY - JOUR
T1 - Phosphate coprecipitation affects reactivity of iron (oxyhydr)oxides towards dissolved iron and sulfide
AU - Kraal, Peter
AU - van Genuchten, Case M.
AU - Behrends, Thilo
N1 - Funding Information:
This work was funded by a grant from the Netherlands Organisation for Scientific Research, NWO Veni grant 863.14.014 to P. Kraal. The work was further supported by NWO DUBBLE grant 195.068.1039 for ESRF beamline BM26A. Case M. van Genuchten acknowledges NWO Veni grant 14400. We gratefully thank the technical support and advice of Dipanjan Banerjee at the DUBBLE beamline during Fe K-edge EXAFS data collection. We thank Marcus Ohl and Oliver Plümper at Utrecht University for TEM analysis of P9-FeOx OXID . Three anonymous reviewers provided insightful feedback that improved the quality of this article.
Publisher Copyright:
© 2022 The Author(s)
PY - 2022/3/15
Y1 - 2022/3/15
N2 - Iron (Fe) cycling exerts strong control on the mobility and bioavailability of the key nutrient phosphate (PO4) in soils and sediments. Coprecipitation of PO4 is known to alter the structure of Fe (oxyhydr)oxides (FeOx), however the environmental fate of PO4-bearing FeOx is not well-understood. Here, PO4-bearing FeOx with 9 mol% coprecipitated PO4 were prepared by Fe(III) hydrolysis and Fe(II) oxidation in the presence of dissolved PO4, in addition to pure FeOx synthesized in PO4-free solutions. The pure and PO4-bearing FeOx were subsequently exposed to different concentrations of dissolved Fe(II) and sulfide (2 and 10 mmol L−1). Mineral transformations and the fate of PO4 were tracked over 7–14 days with wet chemical techniques (including sequential Fe and S extraction) and synchrotron-based Fe K-edge X-ray absorption spectroscopy. Coprecipitation of PO4 affected the rate and extent of FeOx transformation differently for Fe(II) and sulfide. Poorly-ordered PO4-bearing FeOx was preserved in the presence of dissolved Fe(II) while pure ferrihydrite was nearly completely transformed into goethite over 7 days. By contrast, coprecipitation of PO4 rendered FeOx more reactive towards sulfide compared to pure FeOx. Reaction with dissolved sulfide resulted in the formation of non-sulfidized Fe(II) or Fe(II) sulfide under high and low Fe/sulfide ratio, respectively. Under low Fe/sulfide ratio, Fh and PO4-bearing, poorly-ordered FeOx were nearly completely sulfidized after 14 days. Sulfidation of FeOx led to efficient release of PO4 into solution, and at low Fe/sulfide ratio more PO4 was released than expected based on the extent of Fe sulfidation. The results suggest feedback mechanisms of environmental relevance: coprecipitation of strongly-sorbing species such as PO4 disrupts FeOx structure, which affects FeOx reactivity and the overall nutrient or contaminant retention capacity of soils or sediments differently depending on the ambient redox conditions. Specifically, the switch from reducing to sulfidic conditions may be associated with the disproportionate release of nutrients and contaminants.
AB - Iron (Fe) cycling exerts strong control on the mobility and bioavailability of the key nutrient phosphate (PO4) in soils and sediments. Coprecipitation of PO4 is known to alter the structure of Fe (oxyhydr)oxides (FeOx), however the environmental fate of PO4-bearing FeOx is not well-understood. Here, PO4-bearing FeOx with 9 mol% coprecipitated PO4 were prepared by Fe(III) hydrolysis and Fe(II) oxidation in the presence of dissolved PO4, in addition to pure FeOx synthesized in PO4-free solutions. The pure and PO4-bearing FeOx were subsequently exposed to different concentrations of dissolved Fe(II) and sulfide (2 and 10 mmol L−1). Mineral transformations and the fate of PO4 were tracked over 7–14 days with wet chemical techniques (including sequential Fe and S extraction) and synchrotron-based Fe K-edge X-ray absorption spectroscopy. Coprecipitation of PO4 affected the rate and extent of FeOx transformation differently for Fe(II) and sulfide. Poorly-ordered PO4-bearing FeOx was preserved in the presence of dissolved Fe(II) while pure ferrihydrite was nearly completely transformed into goethite over 7 days. By contrast, coprecipitation of PO4 rendered FeOx more reactive towards sulfide compared to pure FeOx. Reaction with dissolved sulfide resulted in the formation of non-sulfidized Fe(II) or Fe(II) sulfide under high and low Fe/sulfide ratio, respectively. Under low Fe/sulfide ratio, Fh and PO4-bearing, poorly-ordered FeOx were nearly completely sulfidized after 14 days. Sulfidation of FeOx led to efficient release of PO4 into solution, and at low Fe/sulfide ratio more PO4 was released than expected based on the extent of Fe sulfidation. The results suggest feedback mechanisms of environmental relevance: coprecipitation of strongly-sorbing species such as PO4 disrupts FeOx structure, which affects FeOx reactivity and the overall nutrient or contaminant retention capacity of soils or sediments differently depending on the ambient redox conditions. Specifically, the switch from reducing to sulfidic conditions may be associated with the disproportionate release of nutrients and contaminants.
KW - Biogeochemical cycles
KW - Chemical sequential extraction
KW - Fe(II)-catalyzed transformation
KW - Ferrihydrite
KW - Iron redox cycling
KW - Lepidocrocite
KW - Phosphorus retention
KW - Sulfidation
KW - X-ray absorption spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85123705410&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2021.12.032
DO - 10.1016/j.gca.2021.12.032
M3 - Article
AN - SCOPUS:85123705410
SN - 0016-7037
VL - 321
SP - 311
EP - 328
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -