Fe-aq(II)-Fe-oxide(III) oxide electron transfer and Fe exchange: effect of organic carbon

作者：Pasakarnis Timothy; McCormick Michael L; Parkin Gene F; Thompson Aaron; Scherer Michelle M^*

来源：Environmental Chemistry, 2015, 12(1): 52-63.

DOI：10.1071/EN14035

Environmental context Concerns about carbon-driven climate change make it critical to better understand how carbon interacts with soils. We examined whether carbon compounds commonly found in soils affect the behaviour of soil iron minerals, and found that iron minerals remain dynamic and mix with the surrounding water, despite the presence of carbon in the water. Our findings suggest that both carbon and trace elements in the minerals may be more mobile and less stable than we previously thought.
Abstract The close association of organic carbon and Fe oxides has been recognised for decades and recently interest in the role of Fe oxides in organic C sequestration has increased. Here we explore the effect of natural organic C on electron transfer and exchange of aqueous Fe-II and Fe in the bulk structure of goethite and magnetite. Using Fe-57 isotope experiments coupled with Fe-57 Mossbauer spectroscopy it is found that electron transfer occurs between aqueous Fe-II and structural Fe-III in both goethite and magnetite in the presence of most organic C compounds, including natural organic matter (NOM), extracellular polysaccharides (EPS), and cell materials. Only a long-chain (39-C) phospholipid containing organic C significantly inhibited electron transfer. Despite evidence for Fe-II-Fe-oxide(III) electron transfer in the presence of NOM, exchange of Fe between the aqueous phase and bulk Fe was less than observed in the absence of NOM. Our findings suggest that electron transfer between aqueous Fe-II and bulk structural Fe in goethite and magnetite is a robust process likely to occur in a variety of organic-rich biogeochemical environments but that Fe exchange may be inhibited by the presence of some C compounds.

• 出版日期2015