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Diffusion of ions and electron shuttles into grain-scale mineral coatings


EMSL Project ID
44645

Abstract

Important reactive phenomena that affect the transport and fate of many elements and contaminants in the subsurface occur at the mineral-water interface, including sorption and electron transfer reactions. Fundamental knowledge of these phenomena are based on observations of ideal mineral-water systems, e.g., studies of molecular scale reactions on single crystal faces or the surfaces of pure mineral powders. Much less is understood about the sediment-water interface in natural environments, which typically have nanometer to micron scale secondary mineral and biogenic coatings on the surfaces of primary mineral grains. Studies of sediment grain coatings from well-characterized field sites will be conducted to determine the nature of diffusion/sorption and electron transfer processes within the coatings. Diffusion of Br, Sr, SO4, As(V), As(III), PO4, U(VI) and two electron shuttles (the humic acid analogue, AQDS, and riboflavin) into grain-scale coatings will be studied to assess the resulting concentration gradients and reactive processes, including sorption, ion exchange, and electron transfer to iron oxide nanoparticulates within the coating regime. In addition, the distribution of organic carbon within these coatings will be mapped and assessed for their role as a potential carbon and electron donor source for Fe(III) oxide reduction. Selected grain/coating regions will be studied by FIB-SEM, TEM, EMPA-WDS, HIM, and ATP at EMSL. Theoretical modeling of the kinetics and biogeochemical reaction processes will be done using equilibrium mass action and mass transfer models that assess species-specific diffusion of the various solutes within the coating regime.

Project Details

Project type
Exploratory Research
Start Date
2011-10-01
End Date
2012-10-07
Status
Closed

Team

Principal Investigator

James Davis
Institution
Lawrence Berkeley National Laboratory

Team Members

Patricia Fox
Institution
Lawrence Berkeley National Laboratory

Michael Wilkins
Institution
Colorado State University

Chongxuan Liu
Institution
Pacific Northwest National Laboratory