Shiel and five co-authors reported early 2013 that Groundwater samples were collected from the Integrated Field Research Challenge field site in Rifle, Colorado, over the course of a bicarbonate-induced U desorption−adsorption experiment. Uranium concentrations and high precision U isotopic compositions (238U/235U) of these groundwater samples were determined and used to assess the impact of bicarbonate-induced U(VI) desorption from contaminated sediments on the 238U/235U of groundwater.
The 238U/235U of groundwater was not significantly impacted by bicarbonate-induced desorption of U(VI) from mineral surfaces or by adsorption of advecting U(VI) from upgradient locations onto those surfaces after the treatment. Assuming this absence of a significant shift in U isotopic composition associated with desorption−adsorption applies to other systems, reduction of U(VI) to U(IV) is expected to be the dominant source of U isotopic fractionation associated with removal of U(VI) from pore water as a result of natural and stimulated reductive pathways.
The authors concluded that changes in the 238U/235U composition of uranium-bearing fluids should be useful in quantifying the extent of reduction.
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