Keywords

chemistry, Tc-99, radiochemistry, redox, environmental chemistry, manganese

Abstract

The environmental mobility of Technetium-99 is inextricably tied to its oxidation state. Under oxidizing conditions Tc-99 predominates as the Tc(VII)O4- anion. This anion has a high solubility and is precluded from sorption on most soil or mineral surfaces, giving it a high environmental mobility. Under reducing conditions, Tc-99 predominates as Tc(IV)O2 or Tc(IV)2S7. Tc(IV) species tend to be insoluble and are therefore immobile. Due to this redox dichotomy, there has been significant interest in developing reductive immobilization strategies for Tc-99, particularly in anoxic environments where Tc(IV) is conventionally assumed to be stable. However, O2 is not the only common environmental oxidant. Many high valent manganese species are environmentally prolific and well known to exist in anoxic and overall reducing environments. These powerful oxidants can create localized oxidizing conditions in otherwise reducing environments. Limited research on the oxidation of Tc(IV) species has left a knowledge gap in the true recalcitrance of such immobilization forms in environmental settings. Our work aims to bridge this knowledge gap by studying the oxidation of Tc(IV) by various, environmentally common, high valent manganese species. Mn(III)-ligand complexes in particular have been overlooked. Up until recently, aqueous Mn(III) was assumed to be absent from the environment due to its disproportionation in aqueous systems without suitable complexing ligands. More recently, Mn(III)-ligand complexes have been shown to be prolific in a variety of natural waters. We have shown that various manganese oxides and Mn(III)-ligand complexes are capable of rapidly oxidizing Tc(IV) to Tc(VII), even in the absence of oxygen, resulting in dissolution of Tc-99 and release to the aqueous phase. This thesis presents novel information on the redox interface chemistry of Tc-99, which is crucial to developing effective remediation methods.

Completion Date

2023

Semester

Fall

Committee Chair

Anagnostopoulos, Vasileios

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Chemistry

Format

application/pdf

Identifier

DP0028095

URL

https://purls.library.ucf.edu/go/DP0028095

Language

English

Release Date

December 2024

Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Campus-only Access)

Campus Location

Orlando (Main) Campus

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Restricted to the UCF community until December 2024; it will then be open access.

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