Speciation of arsenic in sulfidic waters |
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| Authors: | Richard T Wilkin Dirk Wallschläger Robert G Ford |
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| Institution: | (1) U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, 919 Kerr Research Drive, Ada, OK 74820, USA;(2) Environmental and Resource Studies Program, Trent University, 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada; |
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| Abstract: | Formation constants for thioarsenite species have been determined in dilute solutions at 25°C, ΣH2S from 10-7.5 to 10-3.0 M, ΣAs from 10-5.6 to 10-4.8 M, and pH 7 and 10. The principal inorganic arsenic species in anoxic aquatic systems are arsenite, As(OH)3
0, and a mononuclear thioarsenite with an S/As ratio of 3:1. Thioarsenic species with S/As ratios of 1 : 1,2 : 1, and 4 : 1
are lesser components in sulfidic solutions that might be encountered in natural aquatic environments. Thioarsenites dominate
arsenic speciation at sulfide concentrations > 10-4.3 M at neutral pH. Conversion from neutral As(OH)3
0 to anionic thioarsenite species may regulate the transport and fate of arsenic in sulfate-reducing environments by governing
sorption and mineral precipitation reactions. |
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