| Autor: |
Gillispie EC; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Mergelsberg ST; Physical and Computational Sciences Directorate, Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Varga T; Environmental Molecular Sciences Laboratory, Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Webb SM; Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States., Avalos NM; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Snyder MMV; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Bourchy A; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Asmussen RM; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Saslow SA; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States. |
| Abstrakt: |
Ettringite is a naturally occurring mineral found in cementitious matrices that is known for its ability to incorporate environmentally mobile oxyanion contaminants. To better assess this immobilization mechanism for contaminants within cementitious waste forms intended for nuclear waste storage, this work explores how mixed oxyanion contaminants compete for ettringite incorporation and influence the evolving mineralogy. Ettringite was precipitated in the presence of TcO 4 - , IO 3 - , and/or CrO 4 2- , known contaminants of concern to nuclear waste treatment, over pre-determined precipitation periods. Solution analyses quantified contaminant removal, and the collected solid was characterized using bulk and microprobe X-ray diffraction coupled with pair distribution function and microprobe X-ray fluorescence analyses. Results suggest that ≥96% IO 3 - is removed from solution, regardless of ettringite precipitation time or the presence of TcO 4 - or CrO 4 2- . However, TcO 4 - removal remained <20%, was not significantly improved with longer ettringite precipitation times, and decreased to zero in the presence of IO 3 - . When IO 3 - is co-mingled with CrO 4 2- , calcite and gypsum are formed as secondary mineral phases, which allows for oxyanion partitioning, e.g., IO 3 - incorporation into ettringite, and CrO 4 2- incorporation into calcite. Results from this work exemplify the importance of competitive immobilization when assessing waste form performance and environmental risk of contaminant release. |
