Time-dependent Measurements of Dissolution-precipitation Reactions Caused by Caustic Waste Solutions At the Hanford Site Using Synchrotron Computed Microtomography
Abstract
Leaking of caustic (hyper-alkaline) radioactive wastes, generated from plutonium production during the Cold War and stored in underground storage tanks at Hanford Site (Richland, WA), has been detected in the subsurface. The caustic wastes leachate induces primary mineral dissolution (releasing Si) and subsequent secondary precipitation (feldspathoids, such as sodalite and cancrinite) in the sediments. The dissolution-precipitation reactions affect the transport of radioactive elements (90Sr and 137Cs) in the sub-surface through changing the morphology of the sediments. We studied here the changes of the morphology of the sediments caused by exposure of quartz sand or Hanford sediments to simulated tank waste leachates (2 M Na+, 1 M OH-, 1.053 M NO3-, 0.05 M Al3+ and 10-5 M Sr2+) using a series of steady-state-flow saturated column experiments. The 3D structures were determined using synchrotron computed microtomography (CMT) at the National Synchrotron Light Source. Sequential measurements were made at intervals over an exposure time of up to ~620 days with a pixel size of 4 μm in mini columns (ID2.1 mm) packed with quartz sand, or with a pixel size of 11 μm in intermediate size columns (ID19 mm) packed with Hanford sediments. Values for porosity as a function of treatment time were obtained showing major changes. Good agreement was found between the microstructure porosity determinations with results obtained from measurements on the composition of the treatment fluids. The results also show the changes in the three dimensional morphology of the sediment structures as a function of the treatment time. Good agreement was also found between observed and simulated porosity and aqueous chemistry obtained using the reactive transport simulator STOMP. A comparison of the CMT results with complementary high-resolution scanning electron microscopy scans will also be presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.H52C..07W
- Keywords:
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- 1800 HYDROLOGY