2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 299-9
Presentation Time: 9:00 AM-6:30 PM

SOLUBILITY OF URANYL PHOSPHATES IN NANOCLUSTER FORMING ENVIRONMENTS


BOUKDAD, Sara1, LOBECK, Haylie2 and BURNS, Peter C.1, (1)Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, (2)Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, sboukdad@nd.edu

The fate and transport of uranium in the environment is an increasingly important issue as current plans of action are created for geologic repositories. The solubility of uranium bearing materials is of particular concern for industrial-scale spent fuel reprocessing. Uranium-based nuclear fuel dissolution in water can also be a route for uranium release into the environment. Uranyl phosphates may be important secondary mineral phases in various settings involving radionuclide contamination. Uranyl phosphates are of particular importance due to their insolubility in water, only releasing about 50-100 ppm U. Preliminary studies have shown autunite, a calcium uranyl phosphate, releases ~7000 ppm U (as measured in water) when exposed to an alkaline environment containing peroxide. Along with autunite, other uranyl phosphates display similar qualities where the uranium release into solution increases as pH and peroxide concentration increase. At these conditions, the uranium content in the form of uranyl peroxide nanoclusters. This study investigated the role and effect additional cations have on uranium release from uranyl phosphates under nanocluster forming environments. The solubility was measured for three differing cations: calcium (autunite), copper (metatorbernite), and potassium (meta-ankoleite) uranyl phosphates. In order to understand uranium release under such conditions, peroxide concentration and pH levels were manipulated to favor nanocluster formation. Nanocluster formation was characterized by Electrospray Ionization-Mass Spectrometry (ESI-MS), and the concentration of uranium was measured at the end of the experiment using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES).