Selenite Reduction by Mackinawite, Magnetite and Siderite: XAS Characterization of Nanosized Redox Products

Suboxic soils and sediments often contain the Fe(II)-bearing minerals mackinawite (FeS), siderite (FeCO3) or magnetite (Fe3O4), which should be able to reduce aqueous selenite, thereby forming solids of low solubility. While the reduction of selenate or selenite to Se(0) by green rust, pyrite and by...

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Bibliographic Details
Published in:Environmental science & technology 2008-03, Vol.42 (6), p.1984-1989
Main Authors: Scheinost, Andreas C, Charlet, Laurent
Format: Article
Language:English
Subjects:
Applied sciences
Carbonates - chemistry
Chemical reactions
Environmental Processes
Exact sciences and technology
Ferric Compounds - chemistry
Ferrosoferric Oxide - chemistry
Ferrous Compounds - chemistry
Iron
Minerals
Nanoparticles
Oxidation-Reduction
Pollution
Sediments
Sodium Selenite - chemistry
Soils
Spectrum Analysis - methods
X-Rays
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Summary:Suboxic soils and sediments often contain the Fe(II)-bearing minerals mackinawite (FeS), siderite (FeCO3) or magnetite (Fe3O4), which should be able to reduce aqueous selenite, thereby forming solids of low solubility. While the reduction of selenate or selenite to Se(0) by green rust, pyrite and by Fe2+ sorbed to montmorillonite is a slow (weeks), kinetically limited redox reaction as demonstrated earlier, we show here that selenite is rapidly reduced within one day by nanoparticulate mackinawite and magnetite, while only one third of selenite is reduced by micrometer-sized siderite. Depending on Fe(II)-bearing phase and pH, we observed four different reaction products, red and gray elemental Se, and two iron selenides with structures similar to Fe7Se8 and FeSe. The thermodynamically most stable iron selenide, ferroselite (FeSe2), was not observed. The local structures of the reaction products suggest formation of nanoscale clusters, which may be prone to colloid-facilitated transport, and may have a higher than expected solubility.
ISSN:0013-936X
1520-5851
DOI:10.1021/es071573f