Hnin Khaing

Degradation of Organic Complexing Agents by Halophilic Microorganisms in Brines

The potential use of geologic salt beds as terminal repositories for nuclear waste has necessitated research on the interaction of the waste with indigenous microbiota. Microorganisms may affect actinide solubility by degrading organic complexing agents present in the waste. A halophilic bacterium and Archaea indigenous to a salt formation in New Mexico were examined for their ability to degrade acetate, oxalate, citrate, and ethylenediamine tetraacetate under aerobic conditions in low and high-magnesium brines. All complexing agents, except EDTA, were utilized, suggesting that microorganisms indigenous to such repositories can potentially play a beneficial role in mitigating actinide mobility.

Uranium (VI) solubility in carbonate-free ERDA-6 brine

When present, uranium is usually an element of importance in a nuclear waste repository. In the Waste Isolation Pilot Plant (WIPP), uranium is the most prevalent actinide component by mass, with about 647 metric tons to be placed in the repository. Therefore, the chemistry of uranium, and especially its solubility in the WIPP conditions, needs to be well determined. Long-term experiments were performed to measure the solubility of uranium (VI) in carbonate-free ERDA-6 brine, a simulated WIPP brine, at pC{sub H+} values between 8 and 12.5. These data, obtained from the over-saturation approach, were the first repository-relevant data for the VI actinide oxidation state. The solubility trends observed pointed towards low uranium solubility in WIPP brines and a lack of amphotericity. At the expected pC{sub H+} in the WIPP ({approx} 9.5), measured uranium solubility approached 10{sup -7} M. The objective of these experiments was to establish a baseline solubility to further investigate the effects of carbonate complexation on uranium solubility in WIPP brines.