Mobility of arsenic and selected metals during re-flooding of iron- and organic-rich acid-sulfate soil

Edward D. Burton, Richard T. Bush, Leigh A. Sullivan, Scott G. Johnston, Rosalie K. Hocking

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159 Citations (Scopus)


The drainage-induced oxidation of iron-sulfide minerals in acid-sulfate soils has adversely affected large areas of coastal floodplains. Re-flooding of these soils, via the re-establishment of more natural drainage regimes, is a potential remediation approach. Here we describe the mobility of Al, As, Fe, Mn, Ni and Zn during controlled re-flooding of an Fe- and organic-rich acid-sulfate soil material. Soil re-flooding caused the onset of microbially-mediated Fe(III)-reduction, which raised the pH of the initially acidic (pH 3.4) soil to pH 6.0 to 6.5, thereby immobilizing Al. The process of Fe(III)-reduction released high concentrations of FeII and was associated with significant mobilization of As. During the early stages of re-flooding, FeII mobility was controlled by dissolution of schwertmannite (Fe8O8(OH)6SO4) with an ion activity product (IAP) of 1019 ± 2. The mobility of FeII was subsequently controlled by the precipitation of siderite (FeCO3) with an IAP spanning 10- 10 to 10- 7.5. The formation of acid-volatile sulfide (AVS), as a product of SO4-reduction, further retarded the mobility of FeII. Interactions with AVS also strongly immobilized Mn, Ni and Zn, yet had little effect on As which remained relatively mobile in the re-flooded soil. This study shows that the mobilization of As and Fe during soil re-flooding should be considered when planning remediation approaches for acid-sulfate soils.

Original languageEnglish
Pages (from-to)64-73
Number of pages10
JournalChemical Geology
Issue number1-2
Publication statusPublished - 2008
Externally publishedYes


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