This dissertation presents results of a study in which hydrogen was injected into groundwater at a post-leached in-situ recovery (ISR) mining site to stimulate reduction and immobilization of uranium. Approximately 100,000 scf of hydrogen was injected into groundwater recirculated between an injection and extraction well (separated by 130 ft) at ~40 gpm over 66 days. 54 gallons of NaBr solution was co-injected as a tracer. Groundwater quality was subsequently monitored at the injection and extraction wells and eleven monitoring wells over two years.
A three-dimensional non-reactive transport model was fit to the field bromide data by adjusting hydraulic conductivity, porosity and dispersivity. The calibrated model agreed well with the bromide data and was subsequently used to estimate the fraction of "untreated water" (i.e., not amended with H2) captured at the extraction well over time.
Statistical analyses were performed to compare soluble elements (U, Mo, Fe, Mn, Ca, Mg, Na, K), anions (F-, Cl-, NO 3-, HCO3-, SO4 2-), conductivity, alkalinity and pH at the injection, extraction, and monitoring wells before and after hydrogen injection. Uranium at the injection well decreased from ~4.3 to 0.04 mg/L (>99%) after hydrogen injection, whereas concentrations at the extraction well - after accounting for dilution with untreated groundwater - only decreased from ~4.3 to 3.4-3.9 mg/L (10-20%).
Groundwater was subsequently pumped in the reverse direction at ~6 gpm for 330 days. Uranium at both the original injection and extraction wells decreased from ~4.3 to <0.04 mg/L (>98%). In contrast, molybdenum, another constituent of concern, only decreased from ~2.3 mg/L to 0.85 mg/L (~80%) at the original injection well, and actually increased from ~2.3 to 3.4 mg/L (48%) at the original extraction well. Although uranium decreased by >98% at the original injection and extraction wells, no significant changes were observed at the four surrounding monitoring wells where bromide tracer concentrations had increased.
The preceding results suggested that injected hydrogen was consumed near the injection well, resulting in a highly reduced zone of limited area. This interpretation was supported by the results of an electron equivalent balance analysis which indicated that ~91% of the transferred hydrogen was channeled into sulfate reduction.
|Advisor:||Clapp, Lee W.|
|Commitee:||Jones, Kim D., McGehee, Thomas L., Ren, Jianhong, Sai, Joseph O.|
|School:||Texas A&M University - Kingsville|
|School Location:||United States -- Texas|
|Source:||DAI-B 78/12(E), Dissertation Abstracts International|
|Subjects:||Engineering, Mining, Environmental engineering, Geochemistry|
|Keywords:||Biorestoration, Groundwater, Hydrogen, Mining, Reduction, Uranium|
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