HR: 11:35h
AN: H32C-06    [Abstracts]
TI: Oxidation Kinetics of Arsenic(III) by Aquifer Material
AU: * Amirbahman, A
EM: aria@umit.maine.edu
AF: Department of Civil and Environmental Engineeirng, University of Maine, Orono, CA 04469 United States
AU: Kent, D B
EM: dbkent@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Curtis, G P
EM: gpcurtis@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Davis, J A
EM: jadavis@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Laboratory experiments were conducted to study the kinetics of As(III) oxidation by aquifer material collected from the USGS research site on Cape Cod, Massachusetts, USA. Aquifer material consisted of coarse sand and gravel but gravel-size material (greater than 2 mm) with greater than 90 percent quartz. The chemical properties were, however, controlled by coatings on grain surfaces dominated by iron and aluminum oxides and silicates. Five different solid samples with similar specific surface areas (0.6 to 0.9 m2/g) and reductively extractable Fe contents (18 to 26 umoles/m2), but with varying total Mn contents (0.5 to 3.5 umol/m2) were used. Both dissolved and surface-bound As(III) and As(V) concentrations were measured with time up to 250 hr. The As(III) oxidation rate correlated with the solid Mn content. The rate of oxidation increased with increasing As(III) initial concentration and increasing solid Mn content, and decreased somewhat with increasing pH (4 to 7). Under all conditions, dissolved As(V) concentrations were very low. A mathematical model was developed to simulate the kinetics and extent of arsenic speciation and transformation by aquifer material. The model included rate-limited adsorption of As(III) onto both oxidative and non-oxidative sites, rate-limited oxidation of As(III), and equilibrium adsorption of As(V). Rate constants for As(III) adsorption and oxidation, and equilibrium constants for As(V) adsorption were the same for all sediments samples. The observed As(III) oxidation rate here is consistent with previous observations of As(III) oxidation over short transport distances during field-scale transport experiments. The model developed here may be incorporated into groundwater transport models to predict As speciation and transport in chemically heterogeneous systems.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting