Abstract
Technetium-99 (99Tc) is important to the nuclear fuel cycle as a long-lived radionuclide produced in ∼6% fission yield from 235U or 239Pu. In its most common chemical form, namely, pertechnetate (99TcO4-), it is environmentally mobile. In situ hydrogen sulfide reduction of pertechnetate has been proposed as a potential method to immobilize environmental 99TcO4- that has entered the environment. Reactions of 99TcO4- with sulfide in solution result in the precipitation of Tc2S7 except when olefinic acids, specifically fumaric or maleic acid, are present; a water-soluble 99Tc species forms. NMR (1H, 13C, and 2D methods) and X-ray absorption spectroscopy [XAS; near-edge (XANES) and extended fine structure (EXAFS)] studies indicate that sulfide adds across the olefinic bond to generate mercaptosuccinic acid (H3MSA) and/or dimercaptosuccinic acid (H4DMSA), which then chelate(s) the 99Tc to form [99TcO(MSA)2]3-, [99TcO(DMSA)2]5-, or potentially [99TcO(MSA)(DMSA)]4-. 2D NMR methods allowed identification of the products by comparison to 99Tc and nonradioactive rhenium standards. The rhenium standards allowed further identification by electrospray ionization mass spectrometry. 99TcO4- is essential to the reaction because no sulfide addition occurs in its absence, as determined by NMR. Computational studies were performed to investigate the structures and stabilities of the potential products. Because olefinic acid is a component of the naturally occurring humic and fulvic acids found in soils and groundwater, the viability of in situ hydrogen sulfide reduction of environmental 99TcO4- as an immobilization method is evaluated.
Original language | English |
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Pages (from-to) | 13214-13227 |
Number of pages | 14 |
Journal | Inorganic Chemistry |
Volume | 56 |
Issue number | 21 |
DOIs | |
State | Published - Nov 6 2017 |
Externally published | Yes |
Funding
The authors acknowledge support from the U.S. Department of Energy, Office of Basic Energy Sciences, Heavy Element Chemistry program under Grant DE-FG02-09ER16097 and the National Science Foundation under IGERT Award DGE-0965983 (to K.M.R.). MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE), Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. Work was also supported by the U.S. Department of Energy, Office of Nuclear Energy, under DOE Idaho Operations Office Contract DE-AC07-051D14517, as part of the Nuclear Science User Facilities. R.S. was partially supported by Oak Ridge National Laboratory through Subcontract 4000140588. The MU Fellowship in Radiochemistry Program (to J.B.) was supported by a grant to the The Curators of the University of Missouri under Award NRC-HQ-15-G-0036, from the Office of the Chief Human Capital Officer of the Nuclear Regulatory Commission. Any statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the view of the Outreach and Recruitment Branch or the U.S. Nuclear Regulatory Commission.