Physics
Scientific paper
Nov 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004gecoa..68.4519l&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 68, Issue 22, p. 4519-4537.
Physics
11
Scientific paper
The dissolution of uranium was investigated from contaminated sediments obtained at the US. Department of Energy (U.S. DOE) Hanford site. The uranium existed in the sediments as uranyl silicate microprecipitates in fractures, cleavages, and cavities within sediment grains. Uranium dissolution was studied in Na, Na-Ca, and NH4 electrolytes with pH ranging from 7.0 to 9.5 under ambient CO2 pressure. The rate and extent of uranium dissolution was influenced by uranyl mineral solubility, carbonate concentration, and mass transfer rate from intraparticle regions. Dissolved uranium concentration reached constant values within a month in electrolytes below pH 8.2, whereas concentrations continued to rise for over 200 d at pH 9.0 and above. The steady-state concentrations were consistent with the solubility of Na-boltwoodite and/or uranophane, which exhibit similar solubility under the experimental conditions. The uranium dissolution rate increased with increasing carbonate concentration, and was initially fast. It decreased with time as solubility equilibrium was attained, or dissolution kinetics or mass transfer rate from intraparticle regions became rate-limiting. Microscopic observations indicated that uranium precipitates were distributed in intragrain microfractures with variable sizes and connectivity to particle surfaces. Laser-induced fluorescence spectroscopic change of the uranyl microprecipitates was negligible during the long-term equilibration, indicating that uranyl speciation was not changed by dissolution. A kinetic model that incorporated mineral dissolution kinetics and grain-scale, fracture-matrix diffusion was developed to describe uranium release rate from the sediment. Model calculations indicated that 50 95% of the precipitated uranium was associated with fractures that were in close contact with the aqueous phase. The remainder of the uranium was deeply imbedded in particle interiors and exhibited effective diffusivities that were over three orders of magnitude lower than those in the fractures.
Heald Steve. M.
Liu Chongxuan
McKinley James P.
Qafoku Odeta
Wang Zheming
No associations
LandOfFree
Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dissolution of uranyl microprecipitates in subsurface sediments at Hanford Site, USA will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1761626