DEPLETED URANIUM IN SEDIMENTS OF PATROON RESERVOIR: SOLID PHASE SPECIATION AND IMPLICATIONS FOR URANIUM TRANSPORT PROCESSES

From 1958 to 1984 the National Lead Industries plant in Colonie, New York processed depleted uranium (DU), and emitted particles of DU oxide (UO2; 88% wt.% U) into the atmosphere. Sediments of the Patroon Reservoir (1.3 ha), located ~ 1 km downstream from the plant, contain a record of deposition of DU and other heavy metals. The purpose of this study is to determine the size, texture, and solid phase speciation of uranium-bearing phases in the reservoir sediments in order to elucidate uranium transport processes in the watershed. Polished sections of sediment samples, containing 50 to 320 mg/g U, were carbon-coated and analyzed by electron microprobe. Microscopic (5-10 mm diameter), anhedral, uranium-bearing particles were found in samples with the highest uranium concentrations. Semi-quantitative WDS analyses of five of these grains show that the U concentration varies among the grains from 6 to 74 weight percent, with variable amounts of Si, Al, Ca, Fe, and Pb (C, O, and H were not measured). These data rule out DU metal or DU oxide, but otherwise provide few constraints on U mineralogy. The relatively large size and presumed density of the particles precludes transport and deposition by fluvial processes alone. The data are consistent with atmospheric deposition of DU oxide particles followed by alteration within the reservoir sediments. Alternatively, U may have been transported in dissolved form or adsorbed to mineral surfaces, and the observed U particles may have been precipitated directly from sediment pore waters. The small size and poor polishing characteristics of these particles presents a problem for quantitative chemical analysis. Further backscatter electron imaging, as well as particle track analysis will be used to locate additional particles and quantitative WDS analysis will be used to constrain their compositions. In addition to reservoir sediments, soil, and dust samples will also be examined.