title: Formation and structural characterization of thioantimony species and their natural occurrence in geothermal waters.
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.
authors: Environmental Geochemistry, University of Bayreuth, Universitaetsstrasse 30, 95440 Bayreuth, Germany. b.planer-friedrich@uni-bayreuth.de
authors: Britta
authors: B
authors: Planer-Friedrich
authors: Andreas C
authors: AC
authors: Scheinost
mesh_terms: D000838:Anions; D000965:Antimony / Q000032:analysis* / Q000737:chemistry*; D002852:Chromatography, Ion Exchange; D045482:Hot Springs / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000032:analysis; D012996:Solutions; D013054:Spectrophotometry, Atomic; D013438:Sulfhydryl Compounds / Q000032:analysis* / Q000737:chemistry*; D013440:Sulfides / Q000032:analysis; D056928:X-Ray Absorption Spectroscopy
chemical_list: D000838:Anions; D012996:Solutions; D013438:Sulfhydryl Compounds; D013440:Sulfides; D000965:Antimony; D010100:Oxygen