T50 Uranium Fate and Transport in the Environment

Sunday, 9 October 2022
1:30 PM - 5:30 PM
205

IN-SITU REMEDIATION OF URANIUM FOLLOWING ISR MINING

Paper number: T50-9
Program: Technical Sessions
Time: 3:25 PM – 3:45 PM

Authors

Abstract

In-situ recovery (ISR) mining is a common method of extracting uranium (U) through injection of an oxidant to oxidize mineralized U(IV) to soluble U(VI) and a complexing agent to produce mobile U(VI) species. This process often results in elevated uranium concentrations in groundwater post-mining. A promising strategy for remediating groundwater following ISR mining is through in-situ remediation where a reductant is injected into the aquifer to reduce U(VI) back to relatively insoluble U(IV). In this study, we performed several experiments utilizing the chemical reductant dithionite and/or the microbial stimulant acetate to induce U(VI) reducing conditions as a part of the restoration process following ISR mining at the Smith Ranch-Highland Mine in WY. Two push-pull experiments using dithionite demonstrated U(VI) reduction and removal as observed by decreasing U(VI) concentrations and δ238U. However, during injection of dithionite and acetate in larger multi-well experiments, U(VI) concentrations increased significantly due to desorption from aquifer sediments and the reduction/dissolution of ferric solids containing adsorbed U. Thermodynamic considerations imply that ferric solids were preferentially reduced before large-scale U(VI) reduction could begin, and this caused the reductant/stimulant to be consumed before large-scale U(VI) reduction could occur during the cross-hole test. These experiments provide insight into how better understanding restoration redox chemistry and adsorption/desorption are critical for engineering effective remediation strategies.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-379001

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