Fe oxide and organic carbon interactions: implications for global carbon sequestration
EMSL Project ID
44731
Abstract
Iron (Fe) minerals can have large specific surface areas and reactive functional groups, which make them strong sorbents for soil nutrients, contaminants, and organic matter (OM), therefore, stabilizing organic carbon in soils. Organic matters, such as fulvic and humic acids, are important in the chemistry of environmental interfaces because they can change the surface properties (e.g., surface charge) of mineral oxide particles due to their surface-active organic functional groups. Adsorbed OM may interfere with sorption processes on the metal oxide surfaces by changing the characteristics of the electrical double layer at the mineral-water interface, blocking surface sites, or providing a variety of new sites for metal binding. In addition, OM can affect the rate of reductive Fe dissolution and the mineralization pathway. Consequently, any changes in terrestrial Fe chemistry may influence the size and turnover rate of soil carbon pools and thus potentially result in changes in the atmospheric CO2 concentration and the global climate. In the natural environment, pure ferrihydrite is rarely formed. For instance, aluminum, organic acids, or OM can be incorporated in the ferrihydrite. Such foreign materials can affect characteristics and reactivity of Fe oxide minerals. Despite the natural phenomena, there is a gap in our understanding on Fe-OM coprecipitates. Only limited studies have been conducted on the chemical and physical characterization and the reactivity of coprecipitate with other nutrients or contaminants. The objective of this proposed research is to synthesize Fe-OM coprecipitate with various methods, such as hydrolysis vs. oxidation, synthesize with different composition of OM, and then characterize their morphology and reactivity, which can be linked to the bioavailability and reactivity of naturally occurring Fe oxides. This proposed research utilizes resources from national laboratories and EMSL. Scanning transmission X-ray microscopy (STXM) tomography investigates 3 dimensional images of coprecipitates and specific functional groups, interacting with Fe. X-ray absorption spectroscopy investigates the bulk composition of coprecipitates from C, N, and Fe K-edge. Mossbauer spectroscopy will investigate magnetic characteristics of coprecipitates. Transmission electron microscopy (TEM) tomography will capture the 3D images of coprecipitates. Focused ion beam/scanning electron microscopy (FIB/SEM) will slice the coprecipitates, and high resolution TEM (HRTEM) with energy dispersive spectroscopy (EDS) investigate OM and Fe distribution within particles. Furthermore, their redox state will be identified by electron loss spectroscopy (EELS) coupled to the HRTEM.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2011-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Daugherty E.E., G.A. Mckee, R. Bergstrom, S.D. Burton, C. Pallud, R.M. Hubbard, and E.F. Kelly, et al. 2019. "Hydrogeomorphic controls on soil carbon composition in two classes of subalpine wetlands." Biogeochemistry 145, no. 1-2:161–175. PNNL-SA-145302. doi:10.1007/s10533-019-00597-y
Troyer LD, JJ Stone, and T Borch. 2014. "Effect of Biogeochemical Redox Processes on the Fate and Transport of As and U at an Abandoned Uranium Mine Site: an X-ray Absorption Spectroscopy Study." Environmental Chemistry 11(1):18-27. doi:10.1071/EN13129