OVERVIEW OF URANIUM IN-SITU RECOVERY (ISR) RESEARCH BY THE U.S. GEOLOGICAL SURVEY

Uranium in-situ recovery (ISR) currently accounts for 80% of the uranium production in the United States. Uranium ISR methods involve injection of groundwater which has been fortified with oxygen and carbon dioxide to dissolve uranium (and other constituents) through oxidation and carbonate complexation. This essentially reverses the original formation process. Uranium-rich groundwater is then pumped to ion exchange resins where the uranium is extracted, eliminating the need for conventional milling operations. Studies underway in the U.S. Geological Survey (USGS) Central Energy Resources Science Center have been designed to characterize solid phase and groundwater geochemical changes that occur during uranium ISR. In addition, the USGS is working to develop novel restoration methods and examine long-term natural attenuation that may reduce dissolved constituents in the groundwater once mining is complete. The major issue in groundwater restoration involves elevated levels of U, Ra, As, Pb, Cd, Se, Hg, Cl, Mn, Fe, and sulfate following ISR mining. Current activities include: (1) investigating historical and current uranium ISR mining operations and restoration practices at a variety of sites, (2) characterizing uranium roll-front deposits and post-mining groundwater constituents evolved during ISR laboratory simulations (using core from Wyoming, New Mexico, and Texas), (3) developing hydrogeologic and geochemical models to mathematically describe ISR and restoration processes, and (4) performing mechanistic, molecular-level measurements to understand uranium interactions with constituents commonly associated with natural uranium deposits (such as iron sulfide) to develop novel reactive nano-particulate technology to restore groundwater following uranium extraction. These studies are designed to provide a life-cycle analysis of uranium mining, with the goal of understanding the possible influences of uranium ISR on long-term groundwater quality.