Geochemical controls on surficial uranium transport in a waste-burdened mining district: Navajo Nation, NM

GEOC 69

Jamie L. deLemos1, Benjamin C. Bostick2, John L. Durant1, Joshua D. Landis2, Andrew N. Quicksall2, Doug Brugge3, Naomi L. Slagowski1, Christine M. George4, and Johnnye Lewis5. (1) Department of Civil and Environmental Engineering, Tufts University School of Engineering, Medford, MA 02155, (2) Department of Earth Sciences, Dartmouth College, 6105 Fairchild, Hanover, NH 03755, (3) Public Health and Family Medicine, Tufts University School of Medicine, Boston, MA, (4) Department of Civil and Environmental Engineering, Stanford University, P.O. Box 13543, stanford, CA 94309, (5) Community Environmental Health Program, University of New Mexico, College of Pharmacy, Health Sciences Center, MSC 09 5360, Albuquerque, NM 87131
Particulate transport of uranium from residual waste piles during episodic precipitation was anticipated to redistribute uranium to downstream areas in a former uranium mining district. However, analysis of sediment, suspended sediment, vegetation, and surface water downstream of uranium impacted and control sites reveal mean concentrations of uranium at background levels. Geochemical characterization of surficial (0 cm), 20 cm, and 90 cm contaminated sediment samples (U (VI)0 86-117 mg/kg) reveal that uranium is highly soluble and therefore not likely to be transported with mobilized sediment. Treatment of contaminated samples with weak soil solution (pH 8, 5 mM NaHCO3, 2 mM CaCl2, I= 0.012 M), initiates rapid dissolution (10-50%) of uranium within 24 hours. Pore water concentrations of uranium in equilibrium with contaminated sediment reached up to 4.15 mg/L. High dissolved concentrations of uranium were sustained in repeated wetting and drying experiments until uranium in the solid phase was depleted. Kinetics of uranium dissolution are diffusion limited. Solution studies and X-ray adsorption spectroscopy confirm the presence of two sparingly soluble uranyl phases. These phases have been exhausted in surficial, contaminated sediment as well as transported sediment, suggesting that mobilized uranium is associated with the dissolved load.
 

Geochemistry Poster Session
6:00 PM-8:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Geochemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007