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

Abstract

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). 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). In order to remove solution Tc through this reduction process, the Tc-sequestering solid must contain a reducing agent and, ideally, the Tc-sequestering material would function in a large range of chemical environments. For long-term stability, the reduced Tc would preferentially be incorporated into the resulting mineral structure instead of simply being sorbed onto the mineral surface. Here, we report results obtained from batch sorption experiments performed in anoxic and oxic conditions with two sulfide-containing potassium metal sulfide (KMS) materials, known as KMS-2 and KMS-2-SS. In deionized water in anoxic conditions after 15 d of contact, KMS-2 is capable of removing ~45% of Tc and KMS-2-SS is capable of removing ~90% of Tc. The improved performance of KMS-2-SS compared to KMS-2 in deionized water in anoxic conditions appears to be linked both to a higher pHmore » resulting from the batch sorption experiments performed with KMS-2-SS and a higher overall purity of KMS-2-SS. Both materials perform even better in highly caustic (pH~13.5), high ionic strength (8.0 M) simulated Hanford low-activity waste solutions, removing more than 90% Tc after 15 d of contact in anoxic conditions. Post-reaction solids analysis indicate that Tc(VII) is reduced to Tc(IV) and that Tc(IV) is bonded to S atoms in the resulting KMS-2 structure in a Tc2S7 form. In contrast to previous ion exchange experiments with other KMS materials, the batch sorption experiments examining Tc removal cause the initially crystalline KMS materials to lose much of their initial long-range order.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Environmental Management (EM)
OSTI Identifier:
1326140
Report Number(s):
PNNL-SA-116928
Journal ID: ISSN 0897-4756; 49000; 49129; 830403000
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 28; Journal Issue: 11; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
Waste Streams; Removal of TcO4-; Environmental Molecular Sciences Laboratory

Citation Formats

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 TcO 4 – from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials. United States: N. p., 2016. 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 TcO 4 – from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials. United States. https://doi.org/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. Tue . "Removal of TcO 4 – from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials". United States. https://doi.org/10.1021/acs.chemmater.6b01296.
@article{osti_1326140,
title = {Removal of TcO 4 – 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). 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). In order to remove solution Tc through this reduction process, the Tc-sequestering solid must contain a reducing agent and, ideally, the Tc-sequestering material would function in a large range of chemical environments. For long-term stability, the reduced Tc would preferentially be incorporated into the resulting mineral structure instead of simply being sorbed onto the mineral surface. Here, we report results obtained from batch sorption experiments performed in anoxic and oxic conditions with two sulfide-containing potassium metal sulfide (KMS) materials, known as KMS-2 and KMS-2-SS. In deionized water in anoxic conditions after 15 d of contact, KMS-2 is capable of removing ~45% of Tc and KMS-2-SS is capable of removing ~90% of Tc. The improved performance of KMS-2-SS compared to KMS-2 in deionized water in anoxic conditions appears to be linked both to a higher pH resulting from the batch sorption experiments performed with KMS-2-SS and a higher overall purity of KMS-2-SS. Both materials perform even better in highly caustic (pH~13.5), high ionic strength (8.0 M) simulated Hanford low-activity waste solutions, removing more than 90% Tc after 15 d of contact in anoxic conditions. Post-reaction solids analysis indicate that Tc(VII) is reduced to Tc(IV) and that Tc(IV) is bonded to S atoms in the resulting KMS-2 structure in a Tc2S7 form. In contrast to previous ion exchange experiments with other KMS materials, the batch sorption experiments examining Tc removal cause the initially crystalline KMS materials to lose much of their initial long-range order.},
doi = {10.1021/acs.chemmater.6b01296},
url = {https://www.osti.gov/biblio/1326140}, journal = {Chemistry of Materials},
issn = {0897-4756},
number = 11,
volume = 28,
place = {United States},
year = {2016},
month = {6}
}

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