Fe(II)-driven transformation of jarosite to magnetite: mechanism insights and environmental implications

Abstract

Fe(II) commonly serves as a catalyst in environmental systems, driving the transformation of metastable iron minerals into more stable phases and thereby exerting a profound influence on the mobility and fate of metals. However, the underlying mechanisms underpinning this dual role—both catalytic and reactive remain unclear. In this study, jarosite was selected as a representative mineral to investigate its transformation into magnetite. A combination of Fe stable isotope tracing and Mössbauer spectroscopy was employed to track redox processes and structural evolution of iron phases at the molecular level. Transmission electron microscopy (TEM) provided direct evidence of intermediates, including green rust, akaganéite, and magnetite nanocrystals, revealing the crystallization pathway of magnetite formation. Isotope results confirmed that complete electron transfer between aqueous Fe(II) and structural Fe(III) in jarosite occurred within the first 30 min, triggering reductive dissolution and subsequent recrystallization. Meanwhile, Fe(II) released during jarosite dissolution underwent hydrolysis and transformation, thereby contributing to continued magnetite crystallization. These findings offered new insights into the function of Fe(II) in iron mineral transformations, particularly its role in electron transfer and structural evolution.

Graphical abstract

Keywords

Jarosite / Phase transformation / Magnetite / Mössbauer spectroscopy / Fe isotopes tracking

Highlight

	● Time-resolved 57Fe Mössbauer revealed electron transfer in jarosite transformation.
	● Key intermediates were captured, clarifying crystallization pathways.
	● Fe(II) acts both as electron donor and structural component in magnetite formation.

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