State Water Resources Research Institute Program


Project ID: 2009NE183B
Title: Nitrate stimulated oxidative dissolution of U(IV) bearing minerals leading to U mobility in Nebraska groundwater
Project Type: Research
Start Date: 3/01/2009
End Date: 2/28/2010
Congressional District: NE 1
Focus Categories: Nitrate Contamination, Water Quality, Geochemical Processes
Keywords: Nitration reduction, Uranium oxidation, Bacteria
Principal Investigator: Weber, Karrie Anne (University of Nebraska); Snow, Daniel
Federal Funds: $ 20,000
Non-Federal Matching Funds: $ 40,577
Abstract: Soluble uranium (U) is a recognized contaminant in public water supplies in various counties throughout the state of Nebraska. The mechanism driving U mobilization in these environments remains poorly understood. In order to begin to consider mitigation strategies and prevent further contamination of drinking water sources, it is necessary to gain a fundamental understanding of the mechanisms stimulating U mobilization. In the state of Nebraska U originated from the weathering of uranium-rich igneous rocks in the Rocky Mountains and deposited in shallow alluvial or ground water environments as insoluble reduced uranium minerals, such as uraninite and coffinite. These reduced U minerals are subject to reoxidation by available oxidants, such as oxygen and nitrate. The oxidation product exists primarily as a dissolved U(VI) species. It is well recognized that anthropogenic activities such as livestock operations and the application of N onto agricultural fields and urban landscapes have resulted in nitrate contamination of surface and groundwaters in the state of Nebraska. Abiotic and bio-oxidative dissolution of U(IV) coupled to nitrate reduction has been recently recognized as a potential U oxidative mechanism. Oxidative dissolution of U(IV) would result in the subsequent mobilization of U in groundwater. Thus, the influx of nitrate as a primary groundwater contaminant can subsequently influence U mobility resulting in a secondary contaminant in ground water through both biotic and abiotic mechanisms. The objective of this project is to examine the oxidative dissolution of U(IV) minerals coupled to the reduction of nitrate, according to the working hypothesis: Abiotic and biotic catalysis of nitrate-dependent uraninite and coffinite oxidation results in U mobility in Nebraska groundwaters. The working hypothesis will be tested via a series of upflow packed column reactor experiments using shallow subsurface sediments collected within the state of Nebraska. An aqueous matrix containing nitrate will be pumped through the column live and killed column reactors. Aqueous U(VI), nitrate and nitrate reduction products (nitrite, nitrous oxide, dinitrogen, and ammonium) as well as the microbial community will be monitored over the course of the experiment. Together these data will establish the potential role of abiotic and biotic mechanisms mobilizing U in Nebraska groundwaters.

Progress/Completion Report, 2009, PDF
Progress/Completion Report, 2010, PDF

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