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Planer-Friedrich, Britta ; Scheinost, Andreas C.:
Formation and structural characterization of thioantimony species and their natural occurrence in geothermal waters.
In: Environmental Science & Technology.
Bd. 45
(2011)
Heft 16
.
- S. 6855-6863.
ISSN 0013-936X
DOI: https://doi.org/10.1021/es201003k
Abstract
Previously postulated from laboratory studies, the occurrence of antimony-sulfur species in geothermal waters could now be proven using anion-exchange chromatography inductively coupled plasma-mass spectrometry. The two thioantimony species detected by AEC-ICP-MS in oxic synthetic antimonite-sulfide solutions were assigned to tri- and tetrathioantimonate based on their S/Sb ratios and structural characterization by X-ray absorption spectroscopy (XAS). XAS confirmed that the initial species formed under anoxic conditions from antimonite at a 10-fold sulfide excess is trithioantimonite. Trithioantimonite rapidly transforms to tetrathioantimonate in the presence of oxygen or to antimonite at excess OH- versus SH- concentrations, and escapes chromatographic detection. In natural geothermal waters, up to 30% trithioantimonate and 9% tetrathioantimonate were detected. Their occurrence increased at increasingly alkaline pH and with increasing sulfide and decreasing oxygen concentrations. Considering the large sulfide excess (100 to 10 000-fold) the proportion of thioantimonates formed under natural conditions is lower than expected from synthetic solutions. Together with the observed high thioarsenate concentrations (>80%of total arsenic), this indicates that in direct competition with arsenic for a limited source of sulfide, thioantimonates form less spontaneously than thioarsenates. Interactions of arsenic and antimony with sulfur can therefore be decisive for similarities or differences in their environmental behavior.