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Faculty for Biology, Chemistry, and Earth Sciences

Environmental Geochemistry Group - Prof. Dr. Britta Planer-Friedrich

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Master Thesis

Sulfur redox chemistry governs diurnal antimony and arsenic cycles at Champagne Pool, New Zealand

Maria Ullrich (11/2011-09/2012)

Support: Britta Planer-Friedrich

Based on a report of diurnal cycles in antimony and arsenic concentrations at Champagne Pool, New Zealand, sulfur speciation and consequent potential implications for dissolved Sb and As were investigated. During a 24 hour sampling campaign, five sites along the drainage channel of Champagne Pool were sampled every two hours to monitor temporal variations and species transformations within the discharged fluid. Total trace element concentrations in filtered and unfiltered samples were analyzed using ICP-MS, and S, Sb and As species were determined by IC-ICP-MS. Sulfur speciation in the drainage channel was dominated by thiosulfate and sulfide at night, while sulfate prevailed during the day. The distinct diurnal variations suggest this is caused by phototrophic sulfur-oxidizing bacteria metabolizing thiosulfate and sulfide only during daytime, forming sulfate and, as shown by modelling with PhreeqC, elemental sulfur. Sulfide consumption during the day resulted in undersaturation of antimony sulfides, which triggered the additional release of dissolved Sb. For As, diurnal cycles in speciation were much more pronounced, with di- and trithioarsenate forming at night due to the excess of sulfide, and monothioarsenate forming from arsenite and elemental sulfur during daytime. Sulfur speciation was thus found to control Sb and As in terms of both solubility and speciation.

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