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Adsorption and reduction of arsenate during the Fe2+-induced transformation of ferrihydrite

  • Iron (oxyhydr)oxides play an important role in controlling the mobility and toxicity of arsenic (As) in contaminated soils and groundwaters. However, dynamic subsurface geochemical conditions can potentially impact As sequestration since this is highly dependent on the dominant iron mineral phases present and the pathways through which they form. In this study, we investigated the Fe2+-induced transformation of As(V)-bearing ferrihydrite (As-FH) to more crystalline phases under relevant anoxic subsurface conditions. Specifically, we examined the influence of varying Fe2+(aq)/Fe(III)solid¬ ratios on the behavior and speciation of the mineral-bound As species during the mineralogical transformation of As-FH at pH 6.5 for 24 h. At lower Fe2+(aq)/Fe(III)solid¬ ratios (0.5 to 1), goethite, green rust sulfate (GR¬SO4) and lepidocrocite formed within the first 2 hours of the reaction, but only goethite and some unreacted FH remained after 24 h. At Fe2+(aq)/Fe(III)solid¬ ratio = 2, GRSO4Iron (oxyhydr)oxides play an important role in controlling the mobility and toxicity of arsenic (As) in contaminated soils and groundwaters. However, dynamic subsurface geochemical conditions can potentially impact As sequestration since this is highly dependent on the dominant iron mineral phases present and the pathways through which they form. In this study, we investigated the Fe2+-induced transformation of As(V)-bearing ferrihydrite (As-FH) to more crystalline phases under relevant anoxic subsurface conditions. Specifically, we examined the influence of varying Fe2+(aq)/Fe(III)solid¬ ratios on the behavior and speciation of the mineral-bound As species during the mineralogical transformation of As-FH at pH 6.5 for 24 h. At lower Fe2+(aq)/Fe(III)solid¬ ratios (0.5 to 1), goethite, green rust sulfate (GR¬SO4) and lepidocrocite formed within the first 2 hours of the reaction, but only goethite and some unreacted FH remained after 24 h. At Fe2+(aq)/Fe(III)solid¬ ratio = 2, GRSO4 remained stable throughout the 24 h reaction, alongside goethite and unreacted FH. Despite >82% of the As-FH being transformed to goethite  GRSO4 in these reactions, no significant As release (>99.9% removal) was observed. However, while As remained mineral-bound, partial oxidation of the initially added As(V) was reduced to As(III), most likely, by the goethite-Fe2+(aq) redox couple. The extent of As(V) reduction increased from ~40% to ~50%, as the Fe2+(aq)/Fe(III)solid¬ ratio increased from 0.5 to 2. Overall, these results provide important insights into transformation pathways of iron (oxyhydr)oxide minerals in As contaminated, anoxic soils and sediments, and also demonstrate the great impact these can have on As oxidation state and, hence, toxicity and mobility in these environments.zeige mehrzeige weniger

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Autor*innen:Jeffey Paulo H. Perez, Dominique J. Tobler, Andrew N. Thomas, Helen M. Freeman, Knud Dideriksen, Jörg RadnikORCiD, Liane G. Benning
Dokumenttyp:Zeitschriftenartikel
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Italienisch):ACS EARTH AND SPACE CHEMISTRY
Jahr der Erstveröffentlichung:2019
Organisationseinheit der BAM:6 Materialchemie
6 Materialchemie / 6.1 Oberflächen- und Dünnschichtanalyse
Verlag:ACS
Jahrgang/Band:3
Ausgabe/Heft:6
Erste Seite:884
Letzte Seite:894
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Freie Schlagwörter:Ferrihydrite; Goethite; Green rust; Mineral tranformation; XAS; XPS
Themenfelder/Aktivitätsfelder der BAM:Chemie und Prozesstechnik
DOI:10.1021/acsearthspacechem.9b00031
ISSN:2472-3452
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:11.07.2019
Referierte Publikation:Ja
Datum der Eintragung als referierte Publikation:11.07.2019
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