Technetium (VII) Co-precipitation with Framework Aluminosilicates

doi:10.2172/1202823

GSTDTAP > 地球科学

DOI	10.2172/1202823
报告编号	DOE-WSU--0005271
来源ID	OSTI ID: 1202823
	Technetium (VII) Co-precipitation with Framework Aluminosilicates
	Harsh, James B.; Dickson, Johnbull Otah; Pierce, Eric M.; Bargar, John
	2015-07-13
出版年	2015
页数	11
语种	英语
国家	美国
领域	地球科学
英文摘要	Technetium-99 (99Tc), a long-lived radionuclide, is one of the most widespread contaminants within the Hanford subsurface. At some depths, it is only extractable with strong acids, suggesting incorporation into a solid phase. We hypothesized that Tc may have coprecipitated with feldspathoid aluminosilicates under waste tanks that had leaked caustic solutions into the vadose zone. Our objectives were to determine if Tc could be incorporated into the feldspathoids cancrinite and sodalite and under what conditions coprecipitation could occur. Our hypothesis was that sodalite was more likely to incorporate and retain Tc. Our approach was to use known methods of feldspathoid formation in solutions resembling those in Hanford waste tanks contacting sediments in terms of major ion (Na, NO3, OH, Al(OH)4, and Si(OH)4 concentrations. In some cases, Al and Si were supplied from zeolite. We used perrhenate (ReO4) as a surrogate for pertechnetate (TcO4) to avoid the radioactivity. The major findings of this study were 1) ReO4 could be incorporated into either sodalite or cancrinite but the concentration in the solid was < 1% of the competing ion Cl, NO3, or NO2. 2) The small amount of ReO4 incorporated was not exchangeable with NO3 or NO2. 3) In sodalite, NO3 was highly preferred over ReO4 but significant Re-sodalite was formed when the mole fraction in solution (Re/Re+N) exceeded 0.8. 4) A nonlinear relation between the unit cell parameter and amount of Re incorporated suggested that a separate Re-sodalite phase was formed rather than a solid solution. 5) We determined that sodalite preference for sodalite in the presence of different anions increased with the ionic size of the competing anion: Cl < CO3 < NO3 < SO4 < MnO4 < WO4 and significant incorporation did not occur unless the difference in anion radii was less than 12%. 6) Re(VII) was not significantly reduced to Re(IV) under the conditions of this experiment and Re appeared to be a good surrogate for Tc under oxidizing conditions as both oxyanions have the same size. In conclusion, incorporation of TcO4 is unlikely in the close proximity to the tanks where sodalite is likely to form in the presence of high NO3 and other anions much smaller than TcO4.
英文关键词	Technetium, rhenium, Hanford waste tanks, subsurface transport, feldspathoids, sodalite, sequestration.
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来源平台	US Department of Energy (DOE)
引用统计
文献类型	科技报告
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/7054
专题	地球科学
推荐引用方式 GB/T 7714	Harsh, James B.,Dickson, Johnbull Otah,Pierce, Eric M.,et al. Technetium (VII) Co-precipitation with Framework Aluminosilicates,2015.