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Concentration of Uranium Particulates from Soils Using a Novel Density-Separation Technique

Elless, M. P., Timpson, M. E., Lee, S. Y.
Soil Science Society of America journal 1997 v.61 no.2 pp. 626-631
polluted soils, uranium, density, fractionation, mineralogy, minerals, chemical composition, pollution control, geochemistry
Soils contaminated with heavy metals or radionuclides at concentrations above regulatory limits pose an environmental and human health risk. Whereas regulatory limits are only concerned with the “extent” of the contamination, knowledge of the “nature” of the contamination (e.g., oxidation state and mineralogy of the contaminant, particulate vs. adsorbed form, etc.) is necessary for developing optimal treatment strategies. Mineralogical identification of the contaminants provides important information concerning the nature of the contamination because once the mineral form is known, its properties can then be determined from geochemical data. To this end, a new density-fractionation technique called the Magstream density separator was used to concentrate U particulates from U-contaminated soils at a former U.S. Department of Energy U-metal production facility. Results from neutron-activation analysis of each density fraction showed that the U had been concentrated (up to 11-fold) in the heavier fractions. Mineralogical analyses of the density fractions of these soils using x-ray diffraction, scanning-electron microscopy, and an electron microprobe showed the predominance of an autunite [Ca(UO)(PO) · 10–12 HO]-like mineral with lesser amounts of uraninite (UO) and coffinite (USiO) as the U-bearing minerals in these soils. The presence of reduced forms of U in these soils suggests that the optimal remediation strategy requires treatment with an oxidizing agent in addition to a carbonate-based leachant to solubilize and remove U from these soils.