This dissertation combines laboratory experiments and analysis of field samples to examine tungsten (W) geochemistry. Data from low ionic strength experimental solutions at room temperature containing between 0.01 M to 0.0002 M total sulfide and 0.0027 M - 0.0001 M tungstate were analyzed using UV/VIS spectrophotometry. Stability constants have been determined for the formation of mono-thiotungstate log K01= 3.43 ± 0.61, di-thiotungstate log K12 = 3.02 ± 0.61, tri-thiotungstate log K23 = 2.82 ± 0.02, and we estimated the tetra-thiotungstate log K34 ~ 2.34. Analysis of W, Mo, Mn, and Fe concentrations in estuarine surface and pore waters and sediments captured environmental samples from oxic and sulfidic conditions. Both surface waters and sediments demonstrated a positive correlation between W and Fe. Unlike Mo, which was depleted in sulfidic salt marsh pore waters, W was enriched in all pore waters in comparison to overlying waters. Thermodynamic modeling of W and Mo thioanion species in sulfidic pore water samples predicts ≤ 50% of tungstate (WO4 2-) forms thiotungstate species and complete conversion of molybdate (MoO42-) to tetrathiomolybdate (oO4 2-). Unlike tetrathiomolydate that is known to be more particle reactive than molybdate, increases in dissolved W coincide with increases in dissolved sulfide in pore waters, suggesting thiotungstates are less particle reactive than thiomolybdates at circum-neutral pH. Finally, sediment analysis suggests sequestration of W is dependent on surface water salinity in the intermediate marsh sediments, and long-term W entrapment occurs in sulfidic salt marsh sediments.
|Advisor:||Johannesson, Karen H.|
|Commitee:||Datta, Saugata, Flowers, George C., Helz, George R.|
|School:||Tulane University School of Science and Engineering|
|Department:||Earth and Environmental Sciences|
|School Location:||United States -- Louisiana|
|Source:||DAI-B 76/06(E), Dissertation Abstracts International|
|Subjects:||Environmental science, Geochemistry|
|Keywords:||Degree of trace metal pyritization, Thiotungstate stability constants, Trace elements in estuarine waters, Tungsten and molybdenum, Tungsten speciation|
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