Characterization of novel arsenic-iron precipitates formed during biological iron reduction
EMSL Project ID
16095
Abstract
Arsenic (As) is a priority pollutant, the fate of which is in part controlled by reactions with ferrous iron. Ferrous iron is capable of mediating solid phase transformations of soil and sediment solids (e.g. ferrihydrite to goethite, formation of green rust), and reacting with other dissolved constituents to form insoluble precipitates. For example, recent results in our laboratory indicate that ferrous iron directly reacts with As(III) in solution, forming a precipitate with a brucite-like sheet structure. As a consequence, arsenic is sequestered within the solid phase rather than being subject to transport or biological update.We have examined the chemistry of arsenic in column systems containing arsenate (HxAsO43-x) or arsenite (H3AsO3) pre-sorbed to ferrihydrite-coated quartz sand. The iron-reducing bacterium, Shewanella putrefaciens (CN32), was mixed into the ferrihydrite-quartz packed mineral bed to facilitate iron reduction upon initiation of hydrologic flow. Influent solutions were buffered at pH 7.2, and contained lactate as an electron donor. Column solids were harvested upon termination of the experiment after 2-3 weeks. Although appreciable amounts of iron reduction occurred within the columns, we observed approximately 30% less total arsenic elution upon generation of Fe(II) compared to abiotic columns loaded with the same initial concentrations of arsenic. Our hypothesis is that arsenic retention occurs via the precipitation of a green rust-like phase during the reduction of ferrihydrite; this precipitate likely harbors arsenic either within an interlayer domain, or within an Fe(II)/Fe(III)/As(III) sheet structure .
We have employed a number of techniques in an attempt to characterize the As-bearing solid phases in the column, including Fe and As X-ray absorption spectroscopy, SEM-EDS, RAMAN spectroscopy, and synchrotron X-ray diffraction. Although we have gained valuable insight regarding the bulk composition of column solids, we have had limited success in identifying specific phases capable of retaining As. It is our objective, therefore, to utilize the electron microscopy facility housed within the Environmental Molecular Science Laboratory in collaboration with Alice Dohnalkova to identify and visualize the solid phases resulting within the solids of our columns, and in particular to identify the hypothesized As-bearing green rust phases. Characterization of such novel As sequestering reactions is important, since they represent potential retention pathways under anaerobic soil conditions, contradicting the current paradigm that As mobility is enhanced under iron reducing conditions.
Project Details
Project type
Exploratory Research
Start Date
2005-09-05
End Date
2007-03-22
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Borch, T.; Camper, A. K.; Biederman, J. A.; Butterfield, P. W.; Gerlach, R.; Amonette, J. E., Evaluation of Characterization Techniques for Iron Pipe Corrosion Products and Iron Oxide Thin Films. Journal of Environmental Engineering 2008, 134, (10), 835-844.
Borch, T.; Camper, A. K.; Biederman, J. A.; Butterfield, P. W.; Gerlach, R.; Amonette, J. E., Evaluation of characterization techniques for iron pipe corrosion products and iron oxide thin films. Journal of Environmental Engineering 2008, In Press.
Borch, T.; Fendorf, S., Phosphate Interactions with Iron (Hydr)oxides: Mineralization Pathways and Phosphorus Retention Upon Bioreduction. In Adsorption of Metals by Geomedia II: Variables, Mechanisms, and Model Applications, 1 ed.; Barnett, M. O.; Kent, D. B., Eds. Elsevier: Amsterdam, The Netherlands, 2008; Vol. 7, pp 321-348.
Borch T, Y Masue, RK Kukkadapu, and S Fendorf. 2007. "Phosphate Imposed Limitations on Biological Reduction and Alteration of Ferrihydrite Mineralization." Environmental Science & Technology 41(1):166-172.
Borch T, Y Masue, RK Kukkadapu, and S Fendorf. 2007. "Phosphate Imposed Limitations on Biological Reduction and Alteration of Ferrihydrite Mineralization." Environmental Science & Technology 41(1):166-172.
Kocar BD, ML Polizzotto, SG Benner, SC Ying, M Ung, K Ouch, S Samreth, B Suy, K Phan, M Sampson, and S Fendorf. 2008. "Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong delta." Applied Geochemistry 23(11):3059-3071. doi:doi:10.1016/j.apgeochem.2008.06.026
PhosphateImposedLimitationsonBiologicalReductionandAlterationofFerrihydrite
Supporting Information for Phosphate Imposed Limitations in Biological Reduction and Alteration of Ferrihydrite