Oxidation-induced Weathering of Primary Iron-rich Silicates: Scale-dependent Rates and their Controls

• Applicant: Dr. Ricarda Behrens
• Subject Area: Soil Sciences
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467329711

For the understanding of weathering processes in silicate rocks and soils, the determination of weathering rates and their controls is of great importance. A principal weathering process is the oxidation of Fe(II) in primary Fe-rich silicates. It is generally believed that this process initiates and enhances the weathering of these minerals, as it creates new pathways for weathering agents. Despite the importance of structural Fe(II) oxidation for bedrock weathering and soil formation, comparative bulk and in situ (micro- to nanometer-scale) investigations on oxidation-induced chemical and structural transformations (e.g., cation release, lattice distortion, micro fractures) of primary Fe(II)-bearing silicates during weathering are missing. Therefore, the overall aim of this project is to explore the oxidation-induced weathering of biotite, olivine, and pyroxene at the bulk and in situ scale and to elucidate abiotic controls of this process. Specific objectives are to (1) determine bulk mineral and in situ Fe(II) oxidation and cation-release rates, (2) elucidate the role of low molecular weight organic acid anions and reactive oxygen species (ROS) in oxidative silicate weathering, (3) study oxidation-related structural changes, and (4) explore the spatial extent of in situ Fe(II) oxidation. These objectives will be achieved by performing abiotic flow-through and batch reactor experiments. Bulk mineral dissolution, bulk Fe(II) oxidation, and ROS formation will be assessed by wet-chemical analyses, including inductively coupled plasma-optical emission spectrometry, high-performance liquid chromatography, and UV-Vis spectrophotometry. For in situ analyses, a combination of transmission electron microscopy techniques will be employed (high-resolution imaging, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, selected area electron diffraction). In summary, the project will integrate bulk and in situ observations and provide the first comprehensive quantitative information on abiotic oxidative weathering of important primary Fe(II)-bearing silicates. The project will thus contribute to a significant advance in the mechanistic understanding of critical-zone weathering reactions.

• DFG Programme: Research Grants