Bachelor Thesis

Formation and degradation of thioantimonates in comparison to thioarsenates

Sebastian Schmitt (11/2010-08/2011)

Support: Britta Planer-Friedrich

Recent studies revealed a substantial influence of thioantimony and thioarsenic species formation on the arsenic and antimony cycles in natural environments like geothermal systems or anoxic groundwater systems. The objective of this thesis was to determine the influence of antimony on thioarsenic speciation and the influence of arsenic on thioantimony speciation in both synthetic solutions and natural alkaline geothermal waters of Yellowstone National Park, USA. Laboratory studies showed faster kinetics for thioantimonate formation compared to thioarsenate formation. Both thioantimonate and thioarsenate formation increased with increasing ionic strength rather than depending on a high sulfide to metalloid ratio. At low sulfide excess, competition for sulfide between antimony and arsenic prevailed. In Yellowstone National Park, thioantimonates dominated antimony speciation at the hot spring´s sources with a maximum share of 75% of total antimony, whereas thioarsenates were the dominant arsenic species with a maximum of nearly 90% of total arsenic. The natural antimony concentration (maximum: 1.1 µmol/L) was significantly below that of arsenic (maximum: 27 µmol/L). The drainage channels of the four investigated hot springs displayed degradation of thioantimonates and thioarsenates due to step-by-step oxidation via trivalent antimonite and arsenite to pentavalent antimonate and arsenate. Likewise, oxidation occurred during the incubation of natural water samples at ambient water temperature. The two applied sample preservation techniques (i.e. flash freezing and sampling in N2-purged septum bottles) mainly revealed differences in the stabilization of antimonite, which was not found in N2-purged septum bottles but was recovered in frozen samples.