| Autor: |
Chatterjee S; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States., Holfeltz VE; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States., Hall GB; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States., Johnson IE; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States., Walter ED; Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States., Lee S; X-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States., Reinhart B; X-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States., Lukens WW; Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States., Machara NP; United States Department of Energy, Germantown, Maryland 20874, United States., Levitskaia TG; Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, United States. |
| Abstrakt: |
Technetium-99 (Tc), a high yield fission product generated in nuclear reactors, is one of the most difficult contaminants to address at the U.S. Department of Energy Hanford, Savannah River, and other sites. In strongly alkaline solutions typifying Hanford tank waste, Tc exists as pertechnetate (TcO 4 - ) (oxidation state VII) as well as in reduced forms (oxidation state < VII), collectively known as non-pertechnetate (non-TcO 4 - ) species. Designing strategies for effective Tc management, including separation and immobilization, necessitates understanding the molecular structure of the non-TcO 4 - species and their identification in actual tank waste samples. Identification of non-TcO 4 - species would facilitate the development of new treatment technologies effective for dissimilar Tc species. Toward this objective, a spectroscopic library of the Tc(I) [ fac -Tc(CO) 3 ] + and Tc(II, IV, V, VII) compounds was generated and applied to the characterization of the actual Hanford AN-102 tank waste supernatant, which was processed to adjust Na concentration to ∼5.6 M and remove 137 Cs by spherical resorcinol-formaldehyde (sRF) ion-exchange resin. Post 137 Cs removal, the cesium-loaded sRF column was eluted with 0.45 M HNO 3 . As-received AN-102, Cs-depleted effluent, and sRF eluate fractions were comprehensively characterized for chemical composition and speciation of Tc using 99 Tc nuclear magnetic resonance spectroscopy and X-ray absorption spectroscopy. It was demonstrated for the first time that non-TcO 4 - Tc present in the AN-102 tank waste is composed of several low-valent Tc species, including the Tc(I) [ fac -Tc(CO) 3 ] + and Tc(IV) compounds. This is the first demonstration of multiple non-TcO 4 - species co-existing in the Hanford tank waste, highlighting their importance for the waste processing. |
