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SPECIATION OF ARSENIC IN SULFIDIC WATERS
Citation:
Wilkin*, R T., D. Wallschlager, AND R G. Ford*. SPECIATION OF ARSENIC IN SULFIDIC WATERS. GEOCHEMICAL TRANSACTIONS 4(1):1-7, (2003).
Description:
Formation constants for thioarsenite species have been determined in dilute solutions at 25 0C, SH2S from 10-7.5 to 10-3.0 M, SAs 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)30, and a mononuclear thioarsenite with 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)30 to anionic thioarsenite species may regulate the transport and fate of arsenic in sulfate-reducing environments by governing sorption and mineral precipitation reactions.