In redox-effected environments, electron transfer between aqueous Fe(II) and Fe(III)-minerals catalyzes iron mineral transformation and recrystallization processes. While the coexistence of iron minerals is common in nature, it remains unclear how coexisting minerals influence Fe(II)-catalyzed ferrihydrite (Fh) transformation. Here, we used 57Fe and Mössbauer spectroscopy to investigate the role of goethite (Gt) in Fh transformation in-situ. We installed PETE mesh-bags filled with 57Fh or 57Fh+Gt into rice paddy soils (Thailand), tidal flat sediments (Germany), and peat soils (Iceland) for eight weeks. 57Fh+Gt buried in paddy soils lead to more Fh to Gt transformation than the pure 57Fh. In tidal sediments, Fh only transformed into Gt if Gt was initially present. And in peat soils, Gt did not alter the Fh transformation, and no crystalline minerals were formed. Our results demonstrate that the complex composition of soil-solid phases controls iron mineral transformation in different redox-affected environments.

Role of coexisting goethite in ferrihydrite transformation in redox-affected soils and sediments

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