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Journal Article

Vivianite-parasymplesite solid solution: A sink for arsenic in ferruginous environments?

Authors
/persons/resource/jpperez

Perez,  J.P.H.
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Okhrymenko,  M.
External Organizations;

/persons/resource/rblukis

Blukis,  Roberts
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/roddatis

Roddatis,  Vladimir
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/smayanna

Mayanna,  S.
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Mosselmans,  J. F. W.
External Organizations;

/persons/resource/benning

Benning,  Liane G.
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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Fulltext (public)

5022866.pdf
(Publisher version), 70MB

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Citation

Perez, J., Okhrymenko, M., Blukis, R., Roddatis, V., Mayanna, S., Mosselmans, J. F. W., Benning, L. G. (2023): Vivianite-parasymplesite solid solution: A sink for arsenic in ferruginous environments? - Geochemical Perspectives Letters, 26, 50-56.
https://doi.org/10.7185/geochemlet.2325


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5022866
Abstract
Vivianite, a hydrated ferrous phosphate [FeII3(PO4)2 · 8 H2O] that forms in oxygen-poor, but Fe2+-rich conditions is important in nutrient cycling in anoxic environments. In natural vivianites, isomorphic substitution of divalent cations for structural Fe(II) are typical. However, anion substitution is rare; in particular, arsenate (AsVO43−) substitution has never been documented in natural vivianites. Only partial substitution has been reported in synthetic analogues, and parasymplesite [FeII3(AsO4)2 · 8 H2O], the arsenic end member of the vivianite mineral group, is found in hydrothermal deposits. In this study, we detail structural changes in synthesised As-vivianites (FeII3[(PO4)1−x(AsO4)x]2 · 8 H2O) with systematically increased degrees of As(V) substitution (0.22 ≤ x ≤ 0.95). As(V) was successfully incorporated into the vivianite crystal structure, creating a homogenous, solid solution between AsVO43− and PO43−. Like both end members, the intermediate As-vivianites crystallised in the monoclinic system (C2/m space group), and retained the platelet crystal habit of As-free vivianite, even at the highest As(V) substitution. This uniform incorporation of As(V), and its replacement of PO43−, provides a potentially stable sink for arsenic in anoxic soils and sediments, and may have implications in ferruginous early Earth oceans.