Influence of Microscopic Diffusive Process on Uranyl Precipitation and Dissolution in Subsurface Sediments at Hanford Site, USA
Uranium in DOE Hanford sediments was found to be distributed as uranyl silicate precipitates almost exclusively within interiors of sediment grains. The precipitates were minute, generally 1-3 {micro}m across in either radiating or parallel arrays in intraparticle microfractures of a few microns width and variable connectivity to particle surfaces. Grain-scale porosity, tortuosity and diffusivity of tracer (H2O) and U(VI) were measured and imaged using various spectroscopic techniques. Simulations using a microscopic reactive diffusion model suggested that diffusion-limited mass transport generated a favorable thermodynamic condition within the grain microfractures for precipitation and concentration of uranium from waste plumes. The rate and extent of uranyl precipitate dissolution were studied in various electrolytes with variable pH under ambient CO2 pressure. Uranium speciation and distribution before and after dissolution were monitored by spectroscopic and imaging techniques . Experimental, spectroscopic and modeling results collectively indicated that dissolution of uranyl precipitates was controlled by diffusion-limited dissolution kinetics.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC) (US)
- OSTI ID:
- 825903
- Resource Relation:
- Conference: 227th American Chemical Society Meeting, Anaheim, CA (US), 03/28/2004--04/01/2004; Other Information: PBD: 29 Mar 2004
- Country of Publication:
- United States
- Language:
- English
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