Distribution of uranium and thorium in dolomitic gravel fill and shale saprolite

Journal Article · Fri Dec 05 00:00:00 EST 2014 · Journal of Hazardous Materials

DOI:https://doi.org/10.1016/j.jhazmat.2014.11.046· OSTI ID:1408665

Phillips, D. H. ^[1]; Watson, D. B. ^[2]

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1. Queen's Univ., Belfast, Northern Ireland (United Kingdom)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

The objectives of this study were to examine (1) the distribution of U and Th in dolomitic gravel fill and shale saprolite, and (2) the removal of uranium from acidic groundwater by dolomitic gravel through precipitation with amorphous basaluminite at the U.S. DOE Oak Ridge Integrated Field Research Challenge (ORIFRC) field site west of the Oak Ridge Y-12 National Security Complex in East Tennessee. Media reactivity and sustainability are a technical concern with the deployment of any subsurface reactive media. Because the gravel was placed in the subsurface and exposed to contaminated groundwater for over 20 years, it provided a unique opportunity to study the solid and water phase geochemical conditions within the media after this length of exposure. This study illustrates that dolomite gravel can remove U from acidic contaminated groundwater with high levels of Al³⁺, Ca²⁺, NO^3-, and SO₄^2- over the long term. As the groundwater flows through high pH carbonate gravel, U containing amorphous basaluminite precipitates as the pH increases. This is due to an increase in groundwater pH from 3.2 to ~6.5 as it comes in contact with the gravel. Therefore, carbonate gravel could be considered as a possible treatment medium for removal and sequestration ofUand otherpHsensitive metals from acidic contaminated groundwater. Thorium concentrations are also high in the carbonate gravel. Thorium generally shows an inverse relationship with U from the surface down into the deeper saprolite. Barite precipitated in the shallow saprolite directly below the dolomitic gravel from barium present in the acidic contaminated groundwater.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1408665
• Alternate ID(s): OSTI ID: 1249570
• Journal Information: Journal of Hazardous Materials, Vol. 285, Issue C; ISSN 0304-3894
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

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54 ENVIRONMENTAL SCIENCES