March 2, 2014
Journal Article

Geochemical and Mineralogical Investigation of Uranium in Multi–element Contaminated, Organic–rich Subsurface Sediment


Alluvial sediments characterized by an abundance of refractory or lignitic organic carbon compounds and reduced Fe and S bearing mineral phases have been identified through drilling activities at the U.S. Department of Energy’s (DOE) Integrated Field Research Challenge (IFRC) site at Rifle, CO. Regions of the subsurface from which such sediments are derived are referred to as Naturally Reduced Zones (NRZ). We conducted a study with NRZ sediments with the objective to: i.) Characterize solid phase contamination of U and other co-contaminants; ii.) Document the occurrence of potential U host minerals; iii.) Determine U valence state and micron scale spatial association with co-contaminants. Macroscopic (wet chemical batch extractions and a column experiment), microscopic (SEM-EDS), and spectroscopic (Mössbauer, µ-XRF and XANES) techniques were employed. Results showed that sediments’ solid phase had significant concentrations of U, S, As, Zn, V, Cr, Cu and Se, and a remarkable assortment of potential U hosts (sorbents and/or electron donors), such as Fe oxides (hematite, magnetite, Al-substituted goethite), siderite, reduced Fe(II) bearing clays, sulfides of different types, Zn sulfide framboids and multi – element sulfides. Multi-contaminants, micron size (ca. 5 to 30 µm) areas of mainly U(IV) and some U(VI), and/or other electron scavengers or donors such as Se, As, Cr, and V were discovered in the sediments, suggesting complex micron-scale system responses to transient redox conditions, and different extent and rates of competing U redox reactions than those of single contaminant systems. Collectively, the results improve our understanding and ability to predict U and NRZ’s complex behavior and will delineate future research directions to further study both the natural attenuation and persistence of contaminant plumes and their contribution to groundwater contamination.

Revised: April 28, 2014 | Published: March 2, 2014


Qafoku N., B.N. Gartman, R.K. Kukkadapu, B.W. Arey, K.H. Williams, P.J. Mouser, and S.M. Heald, et al. 2014. Geochemical and Mineralogical Investigation of Uranium in Multi–element Contaminated, Organic–rich Subsurface Sediment. Applied Geochemistry 42. PNNL-SA-86519. doi:10.1016/j.apgeochem.2013.12.001