Dissertation
A THERMODYNAMIC INVESTIGATION OF AQUEOUS TECHNETIUM(IV) COMPLEXES
Doctor of Philosophy (PhD), Washington State University
01/2019
Handle:
https://hdl.handle.net/2376/117715
Abstract
Technetium-99represents 6.1% of the fission product yield of U-235. It exists in nature in two main oxidation states; Tc(VII) an environmentally mobile ion, and Tc(IV) an environmentally immobile ion which exists in reducing environments, such as soils or underground repositories. Tc(IV) has a solubility of approximately1×10-7 M in water, but the addition of ligands can increase its solubility and environmental mobility. It is important to investigate the interactions of Tc(IV) with environmentally relevant ligands to better understand Tc behavior in solution. Studies have determined the stability constantsof Tc(IV) with several ligands that can be found in the soil; citrate, acetate, oxalate, EDTA and several polyamino-polycarboxylates. These ligands are sterically hindered, and have several binding sites. Smaller ligands such as F−, Cl−, and Br− need to be studied further, for they are abundant in natural water and soil systems. Previous research on Tc(IV) has focused on the interactions with larger ligands, ignoring the interactions that Tc(IV) has with the background electrolytes used on their systems, which often consist of halides. The purpose of this work is to determine stability constants of Tc(IV)-halide complexes, and to determine the thermodynamic parameters for the complexes. This work will begin by determining the stability constants of Tc(IV) with F−, Cl−, and Br−, then the thermodynamic parameters (ΔG, ΔH and ΔS) of the reaction for halide addition will be attained using van’t Hoff analysis. The central hypothesis of this work is that the solubility of Tc(IV) in aqueous media will decrease as a function of ligand field strength along the spectrochemical series(F>Cl>Br).The rationale for this work is that the determination of Tc(IV) solubility in halide containing systems will aid the understanding of the mobility of Tc(IV) in environmental systems.
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Details
- Title
- A THERMODYNAMIC INVESTIGATION OF AQUEOUS TECHNETIUM(IV) COMPLEXES
- Creators
- Cecilia Eiroa Lledo
- Contributors
- Nathalie A Wall (Advisor)Donald Wall (Committee Member)Kenneth L Nash (Committee Member)James A Brozik (Committee Member)Xiaofeng Guo (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Chemistry, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 161
- Identifiers
- 99900581815701842
- Language
- English
- Resource Type
- Dissertation