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Phosphate loading alters schwertmannite transformation rates and pathways during microbial reduction
Schoepfer, V.A.; Burton, E.D.; Johnston, S.G.; Kraal, P. (2019). Phosphate loading alters schwertmannite transformation rates and pathways during microbial reduction. Sci. Total Environ. 657: 770-780. https://doi.org/10.1016/j.scitotenv.2018.12.082
In: Science of the Total Environment. Elsevier: Amsterdam. ISSN 0048-9697, meer
Peer reviewed article  

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Author keywords
    Acid sulfate systems; Green rust; Stability; Microbial reduction; X-ray diffractometry; X-ray spectroscopy

Auteurs  Top 
  • Schoepfer, V.A.
  • Burton, E.D.
  • Johnston, S.G.
  • Kraal, P., meer

Abstract
    Acid sulfate systems commonly contain the metastable ferric oxyhydroxysulfate mineral schwertmannite, as well as phosphate (PO3−4) - a nutrient that causes eutrophication when present in excess. However, acid sulfate systems often experience reducing conditions that destabilize schwertmannite. Under such conditions, the longterm fate of both schwertmannite and PO3−4 may be influenced by interactions during microbially-mediated Fe (III) and SO2-4 reduction. This study investigates the influence of PO3−4 on Fe(III) and SO2-4 reduction and the subsequentmineralogical transformation(s) in schwertmannite-rich systems exposed to reducing conditions. To accomplish this, varied PO3−4 loadings were established in microbially-inoculated schwertmannite suspensions that were incubated under anoxic conditions for 82 days. Increased PO3−4 attenuated the onset of microbial Fe (III) reduction. This delayed consequent pH increases, which in turn had cascading effects on the initiation of SO2-4 reduction and subsequent mineral species formed. Under zero PO3−4 loading, goethite (αFeOOH) formed first, followed by mackinawite (FeS) and siderite (FeCO3). In contrast, in higher PO3−4 treatments, vivianite(Fe3(PO4)2) and/or sulfate green rust (FeII4 FeIII2(OH)12SO4) became increasingly important over time at the expense of goethite and mackinawite compared to PO3−4- free conditions. The findings imply that PO3−4 loading alters the rates and onset of microbial Fe(III)- and SO2-4 - reduction and the subsequent formation of secondary Febearing phases. In addition, schwertmannite reduction and the associated mineralogical evolution under anoxic conditions appears to sequester large quantities of PO3−4 in the form of green rusts and vivianite.

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