Oxidative transformation of iron monosulfides and pyrite in estuarine sediments

Implications for trace metals mobilisation

Girish Choppala, Richard Bush, Ellen Moon, Nicholas Ward, Zhaohui Wang, Nanthi Bolan, Leigh Sullivan

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Iron monosulfides are the initial iron sulfide minerals that form under reducing conditions in organic-rich sediments. Frequently referred as monosulfidic black ooze (MBO), these sediments exists in a range of anoxic systems including estuaries, coastal wetlands and permeable reactive barriers. The objective of this study was to investigate the transformation of solid phase sulfur, iron fractions and trace metals mobilisation in organic-rich hypersulfidic sediments during dredging. Two sediments from geographically contrasting sites in the Peel-Harvey Estuary were collected and subjected to oxidation through resuspension over 14 days. During oxidation, redox potential rapidly and continuously increased, although minimal change in pH was observed in both sediments. The majority of FeS was oxidised within 48 h. Although not as dynamic as FeS, unusually high rates of FeS 2 oxidation were measured in both sediments at circumneutral pH, with between 39 and 58% of FeS 2 oxidised over 14 days. The rapid oxidation of FeS 2 may be attributed to the presence of nano-size FeS 2 crystals (≈550–860 nm) with a high surface area. Before resuspension, solid bound Fe(total) was most abundant as measured by HCl-extractable Fe(II), followed by organic bound Fe(total) and oxide bound Fe(total). There was a marked decrease in these three fractions in both sediments during resuspension, with an increase in Fe(III) fraction. No significant release of trace metals was observed during resuspension of sulfidic sediments. However, disturbance to these estuarine sediments increases Fe(III) formation and further deteriorates the environment through smothering biological surfaces, deteriorating food sources and the quality of benthic habitats.

Original languageEnglish
Pages (from-to)158-166
Number of pages9
JournalJournal of Environmental Management
Volume186
Issue number2
DOIs
Publication statusPublished - 2017
Externally publishedYes

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