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Title: Removal of TcO 4 from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials

Many efforts have focused on the sequestration and immobilization of 99Tc because the radionuclide is highly mobile in oxidizing environments and presents serious health risks due to its radiotoxicity and long half-life (t 1/2= 213 000 a). We report that one of the more common methods for Tc removal from solution and immobilization in solids is based on reducing Tc from highly soluble Tc (VII) to sparingly soluble Tc (IV). Here, we report results obtained with two potassium metal sulfides (KMS-2 and KMS-2-SS) that are capable of reducing Tc (VII) to Tc (IV). Batch sorption experiments were performed in both oxic and anoxic conditions for 15 d in both deionized water (DIW) and a highly caustic (pH ~ 13.6), high ionic strength (8.0 mol L -1), low-activity waste (LAW) stream simulant solution. Tc removal for both materials in DIW is improved in anoxic conditions compared to oxic conditions as a result of a higher solution pH. In DIW and anoxic conditions, KMS-2 is capable of removing ~45% of Tc, and KMS-2-SS is capable of removing ~90% of Tc. Both materials perform even better in the LAW simulant and remove more than 90% of available Tc after 15 d of contactmore » in anoxic conditions. Postreaction solids analyses indicate that Tc (VII) is reduced to Tc (IV) and that Tc(IV)is bonded to S atoms in a Tc 2S 7 complex. Examination of the materials after Tc removal by X-ray diffraction shows that the initially crystalline KMS-2 materials lose much of their initial long-range order. In conclusion, we suggest a Tc removal mechanism wherein the TcO 4- enters the interlayer of the KMS-2 materials where it is reduced by sulfide, which results in a distorted crystalline structure and a solid-state Tc 2S 7 complex.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [4] ;  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Energy and Environment Directorate
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). W. R. Wiley Environmental Molecular Sciences Laboratory
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
  4. Northwestern Univ., Evanston, IL (United States). Department of Chemistry
Publication Date:
Grant/Contract Number:
AC02-05CH11231; AC06-76RL01830
Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 28; Journal Issue: 11; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Environmental Management (EM); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
OSTI Identifier:
1480726

Neeway, James J., Asmussen, R. Matthew, Lawter, Amanda R., Bowden, Mark E., Lukens, Wayne W., Sarma, Debajit, Riley, Brian J., Kanatzidis, Mercouri G., and Qafoku, Nikolla P.. Removal of TcO4– from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials. United States: N. p., Web. doi:10.1021/acs.chemmater.6b01296.
Neeway, James J., Asmussen, R. Matthew, Lawter, Amanda R., Bowden, Mark E., Lukens, Wayne W., Sarma, Debajit, Riley, Brian J., Kanatzidis, Mercouri G., & Qafoku, Nikolla P.. Removal of TcO4– from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials. United States. doi:10.1021/acs.chemmater.6b01296.
Neeway, James J., Asmussen, R. Matthew, Lawter, Amanda R., Bowden, Mark E., Lukens, Wayne W., Sarma, Debajit, Riley, Brian J., Kanatzidis, Mercouri G., and Qafoku, Nikolla P.. 2016. "Removal of TcO4– from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials". United States. doi:10.1021/acs.chemmater.6b01296. https://www.osti.gov/servlets/purl/1480726.
@article{osti_1480726,
title = {Removal of TcO4– from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials},
author = {Neeway, James J. and Asmussen, R. Matthew and Lawter, Amanda R. and Bowden, Mark E. and Lukens, Wayne W. and Sarma, Debajit and Riley, Brian J. and Kanatzidis, Mercouri G. and Qafoku, Nikolla P.},
abstractNote = {Many efforts have focused on the sequestration and immobilization of 99Tc because the radionuclide is highly mobile in oxidizing environments and presents serious health risks due to its radiotoxicity and long half-life (t1/2= 213 000 a). We report that one of the more common methods for Tc removal from solution and immobilization in solids is based on reducing Tc from highly soluble Tc(VII) to sparingly soluble Tc(IV). Here, we report results obtained with two potassium metal sulfides (KMS-2 and KMS-2-SS) that are capable of reducing Tc(VII) to Tc(IV). Batch sorption experiments were performed in both oxic and anoxic conditions for 15 d in both deionized water (DIW) and a highly caustic (pH ~ 13.6), high ionic strength (8.0 mol L-1), low-activity waste (LAW) stream simulant solution. Tc removal for both materials in DIW is improved in anoxic conditions compared to oxic conditions as a result of a higher solution pH. In DIW and anoxic conditions, KMS-2 is capable of removing ~45% of Tc, and KMS-2-SS is capable of removing ~90% of Tc. Both materials perform even better in the LAW simulant and remove more than 90% of available Tc after 15 d of contact in anoxic conditions. Postreaction solids analyses indicate that Tc(VII) is reduced to Tc(IV) and that Tc(IV)is bonded to S atoms in a Tc2S7 complex. Examination of the materials after Tc removal by X-ray diffraction shows that the initially crystalline KMS-2 materials lose much of their initial long-range order. In conclusion, we suggest a Tc removal mechanism wherein the TcO4- enters the interlayer of the KMS-2 materials where it is reduced by sulfide, which results in a distorted crystalline structure and a solid-state Tc2S7 complex.},
doi = {10.1021/acs.chemmater.6b01296},
journal = {Chemistry of Materials},
number = 11,
volume = 28,
place = {United States},
year = {2016},
month = {5}
}