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Abstract

The most common technology currently used for restoring groundwater at In Situ Recovery (ISR) uranium mining sites is reverse osmosis (RO) and reinjection of the permeate. However, this practice does not restore the formation to its original reduced state, and in many cases groundwater uranium concentrations are not restored to premining baseline levels. Natural attenuation based methods are rarely field tested as a small number available sites and a lack of economic interest in the mining community have historically limited their usage. This study was performed to evaluate effectiveness of introducing dissolved hydrogen into a postmined formation at an ISR mining site to stimulate reduction and immobilization of residual soluble uranium to premining baseline levels. The main objectives of this research project were (1) to develop and optimize a system for minimizing air entrainment during water injection when employing a membrane gas-transfer device for down-hole hydrogen infusion; (2) to assess whether injecting dissolved hydrogen using the membrane gas-transfer device can promote immobilization of dissolved uranium in groundwater to near or below premining concentrations. Approximately 30,000 gallons of groundwater were pumped to the surface and then reinjected into the subsurface while being supplied with dissolved hydrogen using the down-hole membrane gas infusion device. Groundwater was pumped back to the surface after several months to evaluate the extent to which dissolved uranium had been removed. Results of this study indicate an ∼83% reduction in soluble uranium concentration was achieved, while significant increases in indigenous microbial populations were observed and the hydrologic permeability of the aquifer remained in the range of clean sand. These results show enough promise to rate future exploration into the development of bio-remediation and/or membrane gas diffusion techniques as a cost effective method for post ISR mining restoration as an alternative to RO.

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In Situ Bio-Reduction/Immobilization of Uranium at an In Situ Recovery Mining Site Utilizing Membrane Infused Gaseous Hydrogen

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