Utilizing concentrations and isotopes to assess the fate and transport of redox-sensitive elements
Veldhuizen, Hannah
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https://hdl.handle.net/2142/129605
Description
Title
Utilizing concentrations and isotopes to assess the fate and transport of redox-sensitive elements
Author(s)
Veldhuizen, Hannah
Issue Date
2025-04-30
Director of Research (if dissertation) or Advisor (if thesis)
Johnson, Thomas
Doctoral Committee Chair(s)
Johnson, Thomas
Committee Member(s)
Anders, Alison
Druhan, Jennifer
Sanford, Robert
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Antimony
isotope
coal ash
Abstract
The fate and transport of redox-sensitive elements (e.g., As, Se, and Sb) is greatly controlled by their solubility and adsorption affinity which varies depending on the oxidation state. An understanding of the redox processes that control fate and transport is important for many applications including contaminant mobility, mineral formation, and paleo-redox conditions. The work presented here seeks to improve our understanding of the mobility of redox-sensitive elements in various redox conditions and looks at how stable Sb isotopes could be used to track these redox reactions.
Stable isotope ratios of Sb in the environment can provide valuable information on sources and processes such as redox reactions. To investigate the fractionation when Sb(V) was abiotically reduced by sulfide to Sb(III), controlled experiments with Sb(V) and sulfide at a pH of 1 to 8 were performed. The magnitude of isotopic fractionation was much greater at an acidic pH. Variables such as Sb speciation, reaction mechanism, and reaction rate appeared to control the magnitude of Sb isotopic fractionation, but a predictive understanding of those controls could not be extracted from my results because the variability in the experimental conditions were too limited. The microbial reactions of Sb also play a big role in the fate of Sb in the environment. In this study I showed that Sb(V) was reduced to Sb(III) by the microorganism, Desulfuribacillus stibiiarsenatis MLFW-2. The magnitude of isotopic fractionation for microbial Sb reduction was twice that of abiotic Sb reduction. The use of Sb isotopes to track immobilization of Sb by reduction reactions may be possible with added knowledge of Sb isotope shifts in natural systems.
The disposal of coal ash into waste storage ponds has the potential to release toxic elements such as Se and As into the environment. Redox conditions are an important variable to consider when assessing the leaching of redox-sensitive elements from coal ash ponds. The aim of this study was to demonstrate the difference in leaching of redox-sensitive elements from coal ash in O2-saturated and O2-depleted conditions with fluid transport. Batch leaching revealed a large dependence on O2 for elements like Cr, Se, Sb, and U which were more mobile in O2-saturated conditions. Column leaching revealed the reduction and immobilization of Cr and Se by reductants in the coal ash, and the adsorption of V, As, Sb, and U onto solid phases in the ash. These results showed that some elements were quickly released into the effluent while other elements were released then re-adsorbed or coprecipitated with other solid phases. Variable leaching patterns for different elements creates a complex system that may release contaminants in rapid pulses or over long time periods.
The mobility of redox-sensitive elements in the natural environment has impacts on contamination of water and soil. When redox-sensitive elements are present in their mobile form they can be extremely harmful. Understanding more about why and how they move in water is important to assess the risks of these contaminants in the environment.
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