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Title: Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide

Abstract

Here, four simulated waste streams relevant to the vitrification of Hanford nuclear waste were studied to evaluate the removal kinetics of technetium-99 (Tc) and co-mingled Cr(VI) during treatment with solid ferrous hydroxide (Fe(OH)2(s)). Simulants treated with Fe(OH)2(s) were reacted for 24 h and sub-sampled periodically to monitor Tc and Cr removal. Solution sample analysis during the reaction was coupled with solid phase characterization, for example, X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), to establish influence of the solid phase product on Tc and Cr removal rates. Based on these results, the majority of Tc and Cr removal occurs within the first 5 min of simulant contact with Fe(OH)2(s). However, the order in which Tc and Cr are completely removed from each simulant depends on the simulant chemistry, the preferred reduction pathway, and the solid phase product, for example, magnetite (Fe3O4) versus goethite (α-FeOOH). Low pH and low Cr concentrations favor rapid Tc removal, with XRD and XAS confirming that Fe3O4 readily incorporates reduced Tc(IV) into its structure. High pH, high Cr concentrations, and the presence of other co-mingled constituents favor heterogeneous removal of Tc early in the reaction (<1 h) with removal rates often faster than those determined formore » Cr. At reaction times of >1 h, Tc removal slows as homogeneous removal of Cr begins to dominate, concurrent with an increase in the formation of FeOOH as the solid phase reaction product. These results suggest that for complex, high pH waste streams, Tc removal within the first hour after Fe(OH)2(s) treatment is necessary for complete Tc reduction and improved mineral immobilization.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4]; ORCiD logo [2];  [5]; ORCiD logo [6]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Pacific Northwest National Laboratory, Richland, Washington 99354, United States
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. USDOE Office of River Protection (ORP), Richland, WA (United States)
  6. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Pohang Univ. of Science and Technology (POSTECH) (Korea, Republic of)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; USDOE Office of River Protection (ORP); National Research Foundation of Korea (NRF)
OSTI Identifier:
1685049
Grant/Contract Number:  
AC02-05CH11231; AC05-76RL01830; AC02-76SF00515; NRF-2017M2B2B1072374; NRF-2017M2B2B1072404
Resource Type:
Accepted Manuscript
Journal Name:
ACS Earth and Space Chemistry
Additional Journal Information:
Journal Volume: 4; Journal Issue: 2; Journal ID: ISSN 2472-3452
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; nuclear waste; technetium; reduction; mineral incorporation; kinetics; immobilization

Citation Formats

Saslow, Sarah A., Pearce, Carolyn I., Bowden, Mark E., Lukens, Wayne W., Kim, Dong-Sang, Kruger, Albert A., and Um, Wooyong. Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide. United States: N. p., 2019. Web. https://doi.org/10.1021/acsearthspacechem.9b00277.
Saslow, Sarah A., Pearce, Carolyn I., Bowden, Mark E., Lukens, Wayne W., Kim, Dong-Sang, Kruger, Albert A., & Um, Wooyong. Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide. United States. https://doi.org/10.1021/acsearthspacechem.9b00277
Saslow, Sarah A., Pearce, Carolyn I., Bowden, Mark E., Lukens, Wayne W., Kim, Dong-Sang, Kruger, Albert A., and Um, Wooyong. Mon . "Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide". United States. https://doi.org/10.1021/acsearthspacechem.9b00277. https://www.osti.gov/servlets/purl/1685049.
@article{osti_1685049,
title = {Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide},
author = {Saslow, Sarah A. and Pearce, Carolyn I. and Bowden, Mark E. and Lukens, Wayne W. and Kim, Dong-Sang and Kruger, Albert A. and Um, Wooyong},
abstractNote = {Here, four simulated waste streams relevant to the vitrification of Hanford nuclear waste were studied to evaluate the removal kinetics of technetium-99 (Tc) and co-mingled Cr(VI) during treatment with solid ferrous hydroxide (Fe(OH)2(s)). Simulants treated with Fe(OH)2(s) were reacted for 24 h and sub-sampled periodically to monitor Tc and Cr removal. Solution sample analysis during the reaction was coupled with solid phase characterization, for example, X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), to establish influence of the solid phase product on Tc and Cr removal rates. Based on these results, the majority of Tc and Cr removal occurs within the first 5 min of simulant contact with Fe(OH)2(s). However, the order in which Tc and Cr are completely removed from each simulant depends on the simulant chemistry, the preferred reduction pathway, and the solid phase product, for example, magnetite (Fe3O4) versus goethite (α-FeOOH). Low pH and low Cr concentrations favor rapid Tc removal, with XRD and XAS confirming that Fe3O4 readily incorporates reduced Tc(IV) into its structure. High pH, high Cr concentrations, and the presence of other co-mingled constituents favor heterogeneous removal of Tc early in the reaction (<1 h) with removal rates often faster than those determined for Cr. At reaction times of >1 h, Tc removal slows as homogeneous removal of Cr begins to dominate, concurrent with an increase in the formation of FeOOH as the solid phase reaction product. These results suggest that for complex, high pH waste streams, Tc removal within the first hour after Fe(OH)2(s) treatment is necessary for complete Tc reduction and improved mineral immobilization.},
doi = {10.1021/acsearthspacechem.9b00277},
journal = {ACS Earth and Space Chemistry},
number = 2,
volume = 4,
place = {United States},
year = {2019},
month = {12}
}

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