Using Either Hydrogen or Dithionite as Reductant in Uranium Contaminated Groundwater at Post-Leach Uranium Mining Sites, South Texas

Using either Hydrogen or Dithionite as Reductant in Uranium Contaminated Groundwater at Post-Leach Uranium Mining Sites, South TexasAbstract This paper reports on uranium being a major groundwater contaminant in ISL miningsites located in South Texas. This research is about modeling, simulations and studies usingPHREEQC, a computer program from USGS, on how the two (2) reductants hydrogen gas (H2)and dithionite (Na2S2O4) will induce the reduction of U(VI) to U(IV) and the associated speciesin the uranium contaminated groundwater. However, before any development of new technologyand/or techniques in uranium groundwater restoration, an integrated understanding of the sitehydrogeology, geochemistry, and environmental hazards in ISL mining operations are of utmostimportance. ISL produces 90% of uranium mined in the US. In order to assess the extent of uranium remobilization at the end of the life cycle of anin-situ sediment reduction process a series of laboratory scale experiments and computersimulations was conducted using chemical reductants such as hydrogen gas and dithionitesolution. The uranium species that occur naturally in the +6 valence state [U (VI)] willaccumulate through the reduction and under precipitation conditions in the +4 valence state as U(IV). The important question is of how far the presence of uranium deposits is explored andmined by ISL mining method with utmost considerations from the surface environmentalstandpoint and most important groundwater. The deposition of uranium depends on the localredox state of groundwater flow, so if the groundwater is in reducing conditions, there is littleincentive for uranium and allied elements to be mobilized. However, if conditions are oxidizing,a large uranium deposition can extend far down dip. Likewise, uranium decay products (He, Rn,Ra, Pb, Th), have also variable mobility. Basically, the restoration of groundwater is generally the highest single cost and averagesabout 40% of the total costs of decommissioning of uranium mine sites. The results of thesephreeqc simulations and studies will be compared to that of laboratory scale experimentation. A learning module based on the legacy cycle concept is developed that challenges thestudents to think through the processes and steps required to determine the level ofcontamination and the amount of restoration required to return groundwater to safe levels. Thislearning module will be introduced into high school mathematics and science classes during the2011-2012 school year. Assessment of the students’ performance will be carried out andreported.