Iron and arsenic cycling in intertidal surface sediments during wetland remediation

Scott G. Johnston, Annabelle F. Keene, Edward D. Burton, Richard T. Bush, Leigh A. Sullivan

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

The accumulation and behavior of arsenic at the redox interface of Fe-rich sediments is strongly influenced by Fe(III) precipitate mineralogy, As speciation, and pH. In this study, we examined the behavior of Fe and As during aeration of natural groundwater from the intertidal fringe of a wetland being remediated by tidal inundation. The groundwater was initially rich in Fe 2+ (32 mmol L -1) and As (1.81 μmol L -1) with a circum-neutral pH (6.05). We explore changes in the solid/solution partitioning, speciation and mineralogy of Fe and As during long-term continuous groundwater aeration using a combination of chemical extractions, SEM, XRD, and synchrotron XAS. Initial rapid Fe 2+ oxidation led to the formation of As(III)-bearing ferrihydrite and sorption of >95% of the As(aq) within the first 4 h of aeration. Ferrihydrite transformed to schwertmannite within 23 days, although sorbed/coprecipitated As(III) remained unoxidized during this period. Schwertmannite subsequently transformed to jarosite at low pH (2-3), accompanied by oxidation of remaining Fe 2+. This coincided with a repartitioning of some sorbed As back into the aqueous phase as well as oxidation of sorbed/coprecipitated As(III) to As(V). Fe(III) precipitates formed via groundwater aeration were highly prone to reductive dissolution, thereby posing a high risk of mobilizing sorbed/coprecipitated As during any future upward migration of redox boundaries. Longer-term investigations are warranted to examine the potential pathways and magnitude of arsenic mobilization into surface waters in tidally reflooded wetlands.

Original languageEnglish
Pages (from-to)2179-2185
Number of pages7
JournalEnvironmental Science and Technology
Volume45
Issue number6
DOIs
Publication statusPublished - 2011
Externally publishedYes

Fingerprint

Arsenic
Wetlands
Remediation
aeration
Groundwater
arsenic
Sediments
remediation
Iron
wetland
schwertmannite
iron
groundwater
Mineralogy
ferrihydrite
oxidation
Oxidation
sediment
Precipitates
mineralogy

Cite this

Johnston, Scott G. ; Keene, Annabelle F. ; Burton, Edward D. ; Bush, Richard T. ; Sullivan, Leigh A. / Iron and arsenic cycling in intertidal surface sediments during wetland remediation. In: Environmental Science and Technology. 2011 ; Vol. 45, No. 6. pp. 2179-2185.
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Iron and arsenic cycling in intertidal surface sediments during wetland remediation. / Johnston, Scott G.; Keene, Annabelle F.; Burton, Edward D.; Bush, Richard T.; Sullivan, Leigh A.

In: Environmental Science and Technology, Vol. 45, No. 6, 2011, p. 2179-2185.

Research output: Contribution to journalArticle

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AB - The accumulation and behavior of arsenic at the redox interface of Fe-rich sediments is strongly influenced by Fe(III) precipitate mineralogy, As speciation, and pH. In this study, we examined the behavior of Fe and As during aeration of natural groundwater from the intertidal fringe of a wetland being remediated by tidal inundation. The groundwater was initially rich in Fe 2+ (32 mmol L -1) and As (1.81 μmol L -1) with a circum-neutral pH (6.05). We explore changes in the solid/solution partitioning, speciation and mineralogy of Fe and As during long-term continuous groundwater aeration using a combination of chemical extractions, SEM, XRD, and synchrotron XAS. Initial rapid Fe 2+ oxidation led to the formation of As(III)-bearing ferrihydrite and sorption of >95% of the As(aq) within the first 4 h of aeration. Ferrihydrite transformed to schwertmannite within 23 days, although sorbed/coprecipitated As(III) remained unoxidized during this period. Schwertmannite subsequently transformed to jarosite at low pH (2-3), accompanied by oxidation of remaining Fe 2+. This coincided with a repartitioning of some sorbed As back into the aqueous phase as well as oxidation of sorbed/coprecipitated As(III) to As(V). Fe(III) precipitates formed via groundwater aeration were highly prone to reductive dissolution, thereby posing a high risk of mobilizing sorbed/coprecipitated As during any future upward migration of redox boundaries. Longer-term investigations are warranted to examine the potential pathways and magnitude of arsenic mobilization into surface waters in tidally reflooded wetlands.

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