Experimental determination of contaminant metal mobility as a function of temperature, time and solution chemistry. 1997 annual progress report
- Lawrence Livermore National Lab., CA (US)
- Arizona State Univ., Tempe, AZ (US)
'Strontium is significantly more mobile than other hazardous radioactive metals. Its partitioning between aqueous and solid phases is controlled by reactions that occur at the interface between natural waters and minerals. At a groundwater site in Hanford (200-BP-5), the aerial extent of the {sup 90}Sr plume is 100 times larger than the aerial extent of the {sup 137}Cs and the {sup 239}Pu plumes. Similarly, contaminated, perched watertables at INEL have much higher aqueous concentrations of {sup 90}Sr than {sup 137}Cs, presumably because Cs is preferentially sorbed to solids (Duncan 1995). Under high physical flow conditions, such as those in the highly fractured rock at Hanford and INEL, {sup 90}Sr present in plumes may spread off-site and cause contamination of aquifers or other water sources. Geochemical factors that may contribute to the overall mobility of Sr in natural waters are the solubilities of phases such as strontianite (SrCO{sub 3}) and formation of strong complexes with sulfate and nitrate. Although {sup 90}Sr is mobilized in natural waters in these examples, significant concentrations may also be present in solid phases. Sorption experiments using a wide variety of substrates at room temperature have shown that Sr is removed from solution under certain conditions. Additionally, strontianite (SrCO{sub 3}) may precipitate at low Sr concentrations in the pH range of waters in contact with basaltic rocks, which varies between pH 8 and 10. Waters contain variable amounts of carbonate owing to atmospheric interactions; the partial pressure of CO{sub 2} is about 10 x 3.5 atm in air and commonly as high as 10 x 2.5 atm in soils. The objective of this work is to determine the fundamental data needed to predict the behavior of strontium at temperature and time scales appropriate to thermal remediation. The authors approach combines macroscopic sorption/precipitation and desorption/dissolution kinetic experiments, which track changes in solution composition, with direct molecular characterization of strontium in the solid phase using X-ray absorption spectroscopy. These experiments will be used to identify mechanistic geochemical reactions and their thermochemical properties that will be incorporated into geochemical computer codes. This report consists of two sections: (1) a description of the preliminary results of strontium sorption to kaolinite and goethite from pH 4 to 10 at 25, 50, and 80 C and atmospheric CO{sub 2}(g); and (2) a review of the available thermodyanimc data in the is Fe-Sr-Na-NO{sub 3}-CO{sub 2}-H{sub 2}O system.'
- Research Organization:
- Lawrence Livermore National Lab., NM (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
- OSTI ID:
- 13542
- Report Number(s):
- EMSP-55249-97; ON: DE00013542
- Country of Publication:
- United States
- Language:
- English
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