Antimonite binding to natural organic matter: Spectroscopic evidence from a mine water impacted peatland


Antimonite binding to natural organic matter: Spectroscopic evidence from a mine water impacted peatland

Besold, J.; Eberle, A.; Noël, V.; Kujala, K.; Kumar, N.; Scheinost, A.; Lezama Pacheco, J.; Fendorf, S.; Planer-Friedrich, B.

Peatlands and other wetlands are sinks for antimony (Sb). Solid natural organic matter (NOM) has thus been suggested to play an important role in controlling Sb binding in wetland sediments. However, direct spectroscopic evidence for this sequestration mechanism in natural peat samples is still lacking. In order to investigate Sb binding in peat, we sampled and characterized three profiles up to a depth of 80 cm in an Sb-impacted peatland in northern Finland. We used bulk K-edge X-ray absorption spectroscopy to study the speciation of Fe, S and Sb in the peat solid phase. Additionally, we determined the aqueous speciation of Sb in surface and pore waters. Based on linear combination fittings of extended X-ray absorption fine structure spectra, we found that Sb associated to the solid-phase is up to 100% coordinated to organic phenol and/or thiol groups. Even in the presence of iron, organically-bound Sb(III) was the dominant fraction in all peat profiles and across all depths. While aqueous antimonite concentrations were low, Sb(III) species were dominating solid-phase speciation, suggesting a high reactivity of Sb(III) towards peat surfaces. Our findings therefore confirm that Sb binding to solid NOM acts as an important sequestration mechanism under reducing conditions in NOM-rich wetlands.

Keywords: EXAFS; sulfur; iron; antimony; peat

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Publ.-Id: 29265