Tellurium, antimony, and selenium isotopes as indicators of elemental mobility

Redox reactions greatly influence metal and metalloid mobility, as different oxidation states can exhibit diverse geochemical behavior controlling solubility and adsorption affinity. Elucidating these processes is important in a wide range of geochemical applications, such as contaminant mobility, resource extraction, or the oxygenation of early Earth. Stable isotopic fractionation of redox-sensitive elements can be used as a means to identify redox reactions taking place. For example, selenium (Se) isotopes track reductive immobilization of the contaminant Se in groundwater or surface waters. Other isotope systems, like that of tellurium (Te) and antimony (Sb) have yet to be explored in depth and could provide information about biogeochemical processes that control their mobility in modern and ancient environments. The work presented here seeks to improve our understanding of the isotope systematics of Te, Sb, and Se. I examined the potential of Te isotopes as a proxy of atmospheric oxygenation by creating a novel method to measure δ130Te in a suite of paleosols and near-shore sediments ranging from 3.0 Ga to the Cenozoic. The results suggest that Te isotopes may track the initiation of global Te redox cycling triggered by O2 levels at the Great Oxidation Event. For the oxyanions of the toxic metalloids, Sb and Te, one of the largest immobilizing processes is adsorption. Given the importance of this pathway, potential isotope effects induced by adsorption should be studied, as significant contribution from this fractionating process can complicate interpretations of redox-driven isotopic fractionation. I set up several experiments to examine the isotopic fractionation during adsorption of Sb and Te to goethite and illite at pH 6 and 8. The results indicate that isotope effects produced by adsorption are necessary to consider when using the Sb or Te isotope systems to track reduction reactions. Similarly, the isotope fractionation during Se(VI) or Se(IV) reduction may be complicated by other fractionating processes. For example, the oxidative dissolution of reduced Se-bearing phases has been assumed to produce minor isotopic fractionation but has not been studied in depth. I conducted oxidation experiments with selenide-bearing minerals, which revealed the presence of a persistent positive isotopic offset between the oxidized Se(VI) fraction and the mineral. This result has major implications in interpretation of Se isotopic fractionation during reduction, especially in environments with fluctuating redox conditions. Taken together, the results of these studies advance the use of Te, Sb, and Se isotope systems as proxies of elemental mobility.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Wasserman, Naomi Leah

Contributors dc:contributor

• Johnson, Thomas M
• Lundstrom, Craig C
• Druhan, Jennifer L
• Sanford, Robert

• Tellurium
• antimony
• selenium
• stable isotopes
• redox

Statement dc:rights

• Copyright 2020 Naomi Wasserman

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/108689

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/108689