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Examination of Arsenic Speciation in Sulfidic Solutions Using X-ray Absorption Spectroscopy
BEAK, D. G., R. T. WILKIN, R. FORD, AND S. D. KELLY. Examination of Arsenic Speciation in Sulfidic Solutions Using X-ray Absorption Spectroscopy. DOI: 10.1021/es07185 J. Schnoor (ed.), ENVIRONMENTAL SCIENCE AND TECHNOLOGY. American Chemical Society, Washington, DC, 42(5):1643-1650, (2008).
The chemical speciation of arsenic in sulfidic waters is complicated by the existence of thioarsenic species. The purpose of this research was to use advanced spectroscopy techniques along with speciation modeling and chromatography to elucidate the chemical speciation of As in sulfidic solutions. Results of the X-ray absorption spectroscopy (XAS) and modeling show that experimental solutions contain a mixture of arsenites and thioarsenites with increasing substitution of S for O on As with increasing sulfide concentration. There was no evidence of polymeric As species, or transformation of thioarsenites to thioarsenates as suggested in the literature. Additionally the As speciation measured using XAS was consistent with a thermodynamic model for arsenic speciation in sulfidic systems. Our data cast doubt on the existence of thioarsenates in natural waters as have been postulated through chromatographic techniques. Instead the same chromatographic peak positions proposed for thioarsenates can be explained by thioarsenite species. Additionally sample dilution was shown to change species distribution and care should be taken to avoid sample dilution prior to chromatographic analysis.
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Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
GROUND WATER AND ECOSYSTEMS RESTORATION DIVISION
SUBSURFACE REMEDIATION BRANCH