T79 Geologic Energy Research I

Monday, 5 November 2018
8:00 AM - 12:00 PM
Room 145

URANYL PEROXIDE NANOCLUSTER (U60) IN THE PRESENCE OF NA-MONTMORILLONITE, ANORTHITE, AND QUARTZ

Paper number: T79-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

The mobility of uranium in the subsurface environment has been partially addressed by sorption experiments of the uranyl ion (UO22+) to various minerals in diverse geochemical systems. However, research regarding the behavior of uranyl peroxide nanoclusters, such as [(UO2)(O2)(OH)]6060- (U60), in the environment is relatively scarce. These clusters are predicted to form in aqueous environments where alpha radiolysis produces sufficient quantities of hydrogen peroxide under alkaline conditions (e.g., legacy nuclear waste tanks, nuclear reactor accidents, used nuclear fuel cooling pools, geologic repositories) and their formation may significantly impact our current understanding of the fate and transport of U(VI) if they behave differently than (UO22+). Batch sorption experiments were used to examine the sorption of U60 to Na-montmorillonite (SWy-2), anorthite (CaAl2Si2O8), and quartz (SiO2) as a function of U60 concentration, mineral concentration, and pH. Relatively rapid and quantitative removal of U60 from solution was observed in the presence of Na-montmorillonite (SWy-2); however, much less U60 was removed after partial purification of SWy-2. The removal mechanism appears to be promoted by the exchange of Li+ counter ions, normally weakly associated with U60 in solution, for Ca2+ ions naturally present in the clay. In solution, Ca2+ induces aggregation and precipitation of U60. On the contrary, U60 is not removed by anorthite and quartz and persists in the presence of these minerals for at least one month. This is attributed to the low point to zero charge of these minerals, which leads to a negatively-charged mineral surface and repulsion of the negatively charged uranyl peroxide cage. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman spectroscopy were used to analyze the mineral phases before and after reactions with U60. SEM/EDS identified U-rich precipitates with a noticeable wt% of Ca2+ and Raman spectra revealed signals from the symmetric stretch of U=O and O-O vibrations of peroxo groups associated with the clay surface. This research demonstrates that uranyl peroxide clusters like U60 may be more mobile in environmental systems than U(VI), which has the potential to alter our current understanding of the fate and transport of uranium in the geosphere.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-320734

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.