Surface Characterization of Granular Iron from Cores of an In Situ Permeable Reactive Barrier
EMSL Project ID
16113
Abstract
Permeable reactive barriers (PRBs) for in situ groundwater remediation create a complex biogeochemical environment where the surface layer on the grains of iron varies with space and time. Very little data is available on the composition of these surface layers due to the challenges of sampling such materials from the subsurface and handling/analysis in the laboratory. As part of the first field-scale study of a PRB to remediate groundwater that is contaminated with explosives (TNT, RDX), we will obtain cores using the best sampling methods that are currently available. We are arranging to have the resulting samples characterized by several laboratories, using a range of complementary techniques, in order to gain as much information as possible about the processes that are occurring within this PRB.
Other laboratories will perform real time PCR of extracts for microbial community composition, Mossbauer spectroscopy and XRD for phase characterization of the surface precipitates in bulk, SEM and TEM on whole particles and cross-sections for film structure, and BET for surface area. From EMSL, we are most interested in obtaining information on the valence state of elements (especially S) in the surface precipitates by XPS, but other related surface spectroscopies may prove to be useful. At this time, we expect to core the PRB only once, in late July, so there will be only one set of samples, perhaps with a few subsamples. It is possible, however, that interpretation of the results will require follow-up analysis of a small number of "control" samples.
In addition to obtaining a better understanding of the structure and evolution of the iron oxides that form on iron metal in PRB situations, we are particularly interested in sulfur-containing authigenic precipitates. This is because we know that the PRB has removed large amounts of sulfate from the groundwater, very little sulfide is present in the down-gradient water, and sulfate-reducing bacteria are NOT abundant within the PRB. We presume the S is sequestered on the particle surfaces in sulfides, but we need to know more about this before we can postulate specific mechanisms for removal of the sulfate.
At a minimum, this project will yield a major and several minor publications on the PRB in which the data obtained by EMSL might be used. If the collective data set on characterization of these cores materials turns out to be interesting enough, we may separate it to make a publication dedicated to these results.
Project Details
Project type
Exploratory Research
Start Date
2005-08-01
End Date
2006-08-31
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Johnson, R. L., R. B. Thoms, R. O’Brien Johnson, J. T. Nurmi, and P. G. Tratnyek. 2008. Mineral precipitation and flow reduction up-gradient from a zero-valent iron permeable reactive barrier. Ground Water Monitoring & Remediation 28(3): 56-64.