Sr and As mobilization during the microbial reduction of bacteriogenic iron oxide (BIOS)

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Resume:

Bacteriogenic iron oxides (BIOS) naturally occur in a wide range of
environments including wetlands, hydrothermal sea vents and hot springs.
BIOS are essentially composed of neutrophilic iron-oxidizing bacteria and
poorly ordered iron oxides, such as ferrihydrite. Given their high surface
reactivity and surface area, they have been shown to be efficient sorbents
of aqueous contaminants. The present study investigates the redox stability
of naturally occurring BIOS and the fate of their sorb contaminants (As and
Sr). Results indicate that BIOS samples (composed of ferrihydrite and
smaller amouns of lepidocrocite and goethite) from a wetland area and gold
mine tailing undergo rapide microbial reduction in the presence of a well
known iron-reducing bacterium (i.e., Shewanella putrefaciens CN32). In fact,
the reduction rates observed for the various BIOS samples far exceed those
of synthetic iron oxides (ferrihydrite). The results also show that the
presence of sorbed Sr and As (present as outer-sphere and inner-sphere
complexes, respectively) stabilizes BIOS during microbial reduction by
blocking reactive sites onto the iron oxides. Finally, the fate of Sr and As
during reduction mirrors that of Fe(II), indicating that all sorbed
contaminants are released back into solution