Analysis of Iron Mineralogy of clay sediments exposed to reducing conditions
EMSL Project ID
3155
Abstract
Iron associated with sedimentary iron oxide and clay minerals is a ubiquitous source of Fe(3) for assimilatory and dissimilatory microbial Fe-reduction. Previous data has shown that (i) microbial Fe(3) reduction can potentially occur in bulk unsaturated sediments, and (ii) microbial reduction of Fe(3) associated with clay minerals affects the speciation of previously-sorbed metal (Zn2+) in fundamentally different ways than in parallel experiments with Fe-oxide minerals. The combination of these two observations has important implications towards investigations of the natural Fe-cycle and it?s affect on contaminant geochemistry. These experiments seek to provide the Fe-mineralogical information needed prove the potential for biologic Fe-reduction in unsaturated systems and place the metal geochemistry experiment within the proper mineralogical context.
The first set of analyses will follow up on previous work contracted to PNNL in FY-02. These analyses of two sediments from a mesoscale unsaturated column experiment being conducted at the INEEL. Iron in sediments from the packing material was composed of 63% Fe(3)-illite, 16% Fe(2)-illite, 13% hematite, and 8% poorly crystalline/small particle (ps-pc) Fe-oxides. Analysis of Fe in sediments from deep in the column is not complete yet, but initial results indicate that these sediments may not contain pc/sp Fe-oxides and that the ratio of Fe(3)-illite to Fe(2)-illite may be shifted towards Fe(2)-illite. If these results can be verified with 4.2 K M?ssbauer analyses, and additional M?ssbauer analyses (77 K and 4.2 K) of sediments collected from other depths in the column support this observation; then the combination of these data with microbial community structure data currently being collected will demonstrate the potential for significant microbial Fe-reduction in unsaturated, bulk-aerobic sediments with a low organic carbon content. This would represent an exciting new discovery and result in a high quality publication. This proposal seeks to obtain these data. Additional INEEL funds will be targeted toward this work, pending Congressional approval of the FY03 Energy & Water bill.
The second set of analyses will identify the changes in Fe-mineralogy of Fe-bearing natural sediments that have been exposed to Fe-reducing bacteria. M?ssbauer analyses will be conducted on sediments from experiments conducted in the presence and absence of Zn2+. M?ssbauer analyses previously conducted on goethite from parallel experiments may need to be repeated to obtain better model fits. These data will be combined with wet-chemical speciation, XAS, and scanning surface mass-spec data to contrast the effect of microbial Fe-reduction on Zn2+ sorption chemistry on goethite, hematite, HFO, Fe-bearing clay (MNC-71) and Eatonton Hematite Sand. These analyses will focus on the difference between MNC-71 and goethite, and will be incorporated into an ES&T manuscript that discusses these differences in terms of the fundamentally different sorption mechanisms that are operative in the different systems. Pending Congressional approval of the FY03 Energy & Water Bill, additional funds will be targeted toward experiments to extend these findings to INEEL-SDA sediments.
Project Details
Project type
Exploratory Research
Start Date
2002-12-02
End Date
2004-11-15
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Cooper DC, RK Kukkadapu, D Brewe, AJ Coby, FW Picardal, and AL Neal. 2005. "Effects of Sediment Iron Mineral Composition on Microbially Mediated Changes in Divalent Metal Speciation: Importance of ferrihydrite." Geochimica et Cosmochimica Acta 69(7):1739-1759.