CONCENTRATION OF URANIUM PARTICULATES FROM SOILS USING A NOVEL DENSITY-SEPARATION TECHNIQUE

Soils contaminated with heavy metals or radionuclides at concentration s above regulatory limits pose an environmental and human health risk. Whereas regulatory limits are only concerned with the ''extent'' of t he 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 st rategies. Mineralogical identification of the contaminants provides im portant 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 techn ique 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 an alysis of each density fraction showed that the U had been concentrate d (up to Ii-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 predominan ce of an autunite [Ca(UO2)(2)(PO4)(2).10-12H(2)O]- like mineral with l esser amounts of uraninite (UO2) and coffinite (USiO4) as the U-bearin g minerals in these soils. The presence of reduced forms of U in these soils suggests that the optimal remediation strategy requires treatme nt with an oxidizing agent in addition to a carbonate-based leachant t o solubilize and remove U from these soils.