title: Distribution of uranium and thorium in dolomitic gravel fill and shale saprolite.
abstract: 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 Al(3+), Ca(2+), 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 of U and other pH sensitive 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.
authors.affiliation: Environmental Engineering Research Centre, School of Planning, Architecture, and Civil Engineering, Queen's University of Belfast, Belfast BT9 5AG, Northern Ireland.
authors.forename: D H
authors.initials: DH
authors.lastname: Phillips
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, 37831 TN, USA. Electronic address: watsondb@ornl.gov.
authors.forename: D B
authors.initials: DB
authors.lastname: Watson
mesh_terms: D000534:Alum Compounds / Q000737:chemistry; D002119:Calcium Carbonate / Q000737:chemistry*; D011232:Chemical Precipitation; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000737:chemistry*; D011848:Radioactive Pollutants / Q000032:analysis* / Q000737:chemistry; D013910:Thorium / Q000032:analysis*; D014501:Uranium / Q000032:analysis* / Q000737:chemistry
chemical_list: D000534:Alum Compounds; D011848:Radioactive Pollutants; D014501:Uranium; D013910:Thorium; D002119:Calcium Carbonate; D008274:Magnesium; C028042:calcium magnesium carbonate
keywords: Amorphous basaluminite; Barite; Groundwater contamination; Oak ridge integrated field research challenge (ORIFRC); Thorium; Uranium