HR: 16:30h
AN: B24B-03    [Abstracts]
TI: Arsenic Retention under Static and Dynamic Flow Conditions During Active Iron and Sulfate Reduction
AU: * Quicksall, A N
EM: aquick@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Saalfield, S
EM: samantha.saalfield@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Landis, J D
EM: josh.landis@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Renshaw, C E
EM: carl.renshaw@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Bostick, B C
EM: bbostick@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AB: Biological, physical and chemical parameters impact the speciation and phase associations of adsorbed metals and metalloids on iron hydroxides. In particular, iron- and sulfate-reducing conditions play an important role in their transport and fate in the environment. Here, we examine the effect of chemically and biologically-mediated reduction of sulfate and iron (hydr)oxides and sorbed arsenic in a series of column and batch incubation experiments using synthetic mineral suspensions and/or natural sediments. Arsenic-bearing natural sediments were collected from the Coeur d'Alene River area in northern Idaho and the upper Mekong delta in Cambodia to contrast heavily concentrated anthropogenic and widely disseminated arsenic sources. Sediment samples used in batch incubations were amended with growth media to stimulate indigenous microbial growth. Each sediment type was incubated in static batch incubations containing acetate or lactate. Select incubations also included molybdate to suppress sulfate reduction. Dynamic flow experiments were also performed in which packed columns of soils or As-bearing iron (hydr)oxide coated sand were reduced by sulfide produced in situ through sulfate reduction or the direct addition of sulfide. Solid phase products were identified by bulk and microfocused X-ray absorption spectroscopy, fluorescence and diffraction. In these experiments, iron forms a number of iron minerals, releasing As into solution. Under conditions favoring iron reduction alone, significant As was released into solution; however, little As was released to solution when sulfate reduction was stimulated in batch systems. Under dynamic flow conditions, at least some arsenic was released in all incubations. Flow rate strongly influenced the extent of As sequestration. Some, but not all, of the enhanced sequestration of arsenic in static systems appears to be tied to the production of arsenic sulfides or the re-adsorption of arsenite. The dependence of As retention on flow indicate that reduction and adsorption/desorption kinetics, quantified with reactive transport modeling, play an intrinsic role in As retention in these systems.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0463 Microbe/mineral interactions
DE: 0486 Soils/pedology (1865)
DE: 0488 Sulfur cycling
SC: Biogeosciences [B]
MN: Fall Meeting 2005