An in-situ Study of the Aqueous Speciation of Uranium (VI) Under Hydrothermal Conditions

Author

Diwash Dhakal, Missouri State UniversityFollow

Date of Graduation

Spring 2019

Degree

Master of Science in Materials Science

Department

Physics, Astronomy, and Materials Science

Committee Chair

Robert Mayanovic

Abstract

Rigorous study of the speciation distribution of uranyl-chloride bearing solutions under hydrothermal conditions is important to understand the transport mechanism of uranium underground, which is of uttermost interest to parties studying the geological uranium deposits and those studying the possibilities of geological repositories for spent nuclear waste. I report an in-situ Raman spectroscopic study of the speciation distribution of aqueous uranyl-chloride complexes upto 500°C conducted using a HDAC as the high PT spectroscopic cell. The samples studied contained the species UO₂²⁺, UO₂Cl⁺, UO₂Cl₂⁰ and UO₂Cl₃^- with varying contributions at different temperature and chloride concentration conditions. Raman vibrational peak positions and the FWHM were determined for each of the identified species, and speciation distribution graphs were plotted for different temperature and concentration points. The results obtained are in good agreement with the published room temperature data and also with a high temperature study performed using UV-Vis spectroscopy technique. To confirm and complement the knowledge obtained from optical spectroscopy techniques like Raman spectroscopy and UV-Vis spectroscopy, x-ray absorption spectroscopy experiments are very useful, but the use of radioactive samples under high pressure and temperature conditions in synchrotron x-ray facilities requires strict protocols and a special radiological containment system. I designed and assembled a radiological enclosure system for HDAC suited for synchrotron x-ray absorption spectroscopy experiments on aqueous actinide samples upto high temperature and pressure. This enclosure was successfully tested at APS and SSRL after the approval from radiological safety committee of the respective facilities. XAS data were collected from the uranyl samples upto 500°C and were found to be of comparable quality to those from similar experiments on non-rad samples without the use of enclosure. One representative set of x-ray absorption spectra for aqueous uranyl-chloride bearing sample upto 500°C is presented in this thesis.

Keywords

uranium speciation, hydrothermal diamond anvil cell, Raman spectroscopy, xray absorption spectroscopy, high pressure high temperature

Subject Categories

Environmental Indicators and Impact Assessment | Environmental Monitoring | Geochemistry | Geological Engineering | Inorganic Chemistry | Materials Chemistry | Mineral Physics | Nuclear | Oil, Gas, and Energy | Optics | Radiochemistry

Copyright

© Diwash Dhakal

Recommended Citation

Dhakal, Diwash, "An in-situ Study of the Aqueous Speciation of Uranium (VI) Under Hydrothermal Conditions" (2019). MSU Graduate Theses/Dissertations. 3381.
https://bearworks.missouristate.edu/theses/3381