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| - Continuum between Sorption andPrecipitation of Fe(III) on MicrobialSurfaces
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| - Bacteria are a widespread, abundant, geochemicallyreactive component of aquatic environments. However,their role in the formation of secondary reactive surfacephases such as iron oxides or in the direct sorption of metalcontaminants has yet to be quantitatively described.Here, we compare the formation of iron oxides on bacterialcell surfaces to their formation abiotically (no bacteriapresent) over a range of both Fe(III) concentration (10-2−10-4.5 M) and pH (2−4.5) in the laboratory. Iron sorptionand subsequent precipitation reactions at bacterial surfaceswere modeled using current geochemical approaches.Solid-phase partitioning of Fe(III) as hydrous ferric oxide(HFO) was enhanced in the presence of a variety of bacteriaover that seen in abiotic controls. The onset of HFOformation occurred at lower pH values and in greaterquantities at any given pH in the bacterial treatments. Fe(III) reactions at bacterial surfaces follow a clearcontinuum between sorption and precipitation that can bequantitatively described using geochemical principlesand modeled using surface precipitation theory; to dateonly demonstrated for inorganic surfaces. These resultsshow that the reactions at biological surfaces are likely tobe important in determining the spatial distribution ofiron oxides in nature and thus the reactive transport ofmetals in aqueous environments.
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