Investigation of the stability of secondary precipitates incorporated with contaminants
EMSL Project ID
5891
Abstract
GoalsThe principal goal of the proposed work is to assess the molecular nature and stability of radionuclide (133Cs, 90Sr, and 129I) immobilized during formation of secondary precipitates at the mineral surfaces of Hanford sediments with caustic leaking tank wastes. Because of the sensitive issues in EMSL(Nonradioactive materials only), we will simulate secondary precipitates with non-radioactive materials (Cs, Sr, and I) as analogues for key radionuclides. Our prior studies have shown that Cs and Sr are incorporated into secondary precipitates such as zeolites and feldspathoids that become increasingly recalcitrant to ion exchange and chemical extraction with long-term weathering of specimen clays and Hanford sediments. Therefore, it is necessary to examine systematically the dependence of reaction mechanisms on solution chemistry and solid-to-solution ratio to develop a clear representation of near-field to far-field conditions. The environmental stability of the sorbent weathering products including non-crystalline precipitates, zeolites and feldspathoids, particularly with respect to desorption of radionuclides, dissolution and dispersion will be assessed. Specific objectives of the proposed work are:
(1) Determine the rate and extent of contaminant release by desorption, dissolution and dispersion of weathered Hanford sediments including contaminants incorporated. Previously established dissolved and secondary precipitated phases will be contacted with normal solution germane to pore water condition in the Hanford vadose zone soils.
(2) Determine the molecular nature of contaminant binding sites in neo-formed precipitates and reacted sediments by conjunctive use of microscopy and spectroscopy.
(3) Integrate macroscopic, microscopic and spectroscopic approaches to distinguish labile and recalcitrant contaminant binding sites and their dependence on molecular structure, reaction time and system composition.
Approach and necessary equipments
Batch dissolution/precipitation and column experiments using Hanford sediments have been conducting now in the University of Arizona and PNNL. R.Jeff Serne at PNNL is responsible for carrying out saturated and unsaturated flow column experiments.
Since mineral dissolution/secondary precipitation and its stability including incorporated contaminants are very sensitive to the mineral surfaces, X-ray Photoelectron Spectroscopy (XPS), a surface sensitive technique, will be the best to determine the changes at the mineral surfaces and stability of secondary precipitates. Using XPS, different chemical composition or changes at the mineral surfaces of secondary precipitates including contaminants of interests will be revealed to test their stability under circumneutral pH and ionic strength conditions. In addition to XPS, XRD, FTIR, FESEM, TEM, NMR, and analytical equipment such as ICP-MS or ICP-OES will be used to investigate possible modification of secondary precipitates and potential release of contaminants due to the dissolution of secondary precipitates.
Project Details
Project type
Exploratory Research
Start Date
2003-12-16
End Date
2005-12-22
Status
Closed
Released Data Link
Team
Principal Investigator
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Um W, G Wang, and RJ Serne. 2012. "The effects of secondary mineral precipitates on 90Sr mobility at the Hanford Site, USA." Abstract submitted to Water-rock interaction, Avignon, France. PNNL-SA-91348.
Um W, RJeffrey Serne, SB Yabusaki, and AT Owen. 2005. "Enhanced radionuclide immobilization and flow path modifications by dissolution and secondary precipitates ." Journal of Environmental Quality 34(4):1404-1414.
Wang G, and W Um. 2013. "Facilitated Strontium Transport by Remobilization of Strontium-Containing Secondary Precipitates in Hanford Site Subsurface." Journal of Hazardous Materials 248-249:364-370. doi:10.1016/j.jhazmat.2013.01.021