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GEOCHEMICAL MODELING OF ARSENIC SPECIATION AND MOBILIZATION: IMPLICATIONS FOR BIOREMEDIATION
Citation:
LEE, M., J. A. Saunders, R. T. WILKIN, AND S. MOHAMMAD. GEOCHEMICAL MODELING OF ARSENIC SPECIATION AND MOBILIZATION: IMPLICATIONS FOR BIOREMEDIATION. ISBN13: 978084123913, Chapter 29, O'Day, Vlassopoulos, Meng, and Benning (ed.), Advances in Arsenic Research. Oxford University Press, Cary, NC, , 398-413, (2005).
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Description:
Geochemical modeling techniques were used to examine the biogeochemical linkages between Fe, S, and As in shallow alluvial aquifers. We modeled: 1) the adsorption and desorption of As on the surface of hydrous ferric oxides (HFO’s) in stream beds under aerobic conditions; 2) reductive dissolution of HFO by iron-reducing bacteria in anaerobic conditions; and 3) precipitation and sorption of As under sulfate-reducing conditions. The modeling results indicate that reductive dissolution of HFO, rather than desorption, is the main trigger leading to the release of As under near-neutral pH conditions. Dissolved arsenic may be removed by co-precipitation or precipitation with iron or arsenic sulfides under reducing conditions. However, the formation of soluble thioarsenite species at high H2S/Fe ratios would enhance As mobility. Moreover, As concentrations would remain high in Fe-free solutions when the precipitation of arsenic sulfide solids (i.e., orpiment or realgar) is kinetically prohibited or when their amorphous precursors are formed. Geochemical modeling of sulfate reduction shows the Eh effect on mineral precipitation and pH controls on the sorption of As in acidic waters. As(V) sorbs strongly onto the protonated sites of HFO over the pH range of 3 to 6. As(III) sorption is also favored by increasing pH, however, As(III) desorbs and becomes mobilized at very low oxidation state as it reacts with reduced sulfur to form thioarsenite complexes. This study demonstrates the importance of using geochemical modeling techniques to evaluate the transport and mobility of As in natural waters.
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GEOCHEMICAL MODELING OF ARSENIC SPECIATION AND MOBILIZATION: IMPLICATIONS FOR BIOREMEDIATION