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Title: Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications

Abstract

At the Hanford Site in southeastern Washington State, radionuclide (Tc-99/I-129) laden liquid wastes have been discharged to ground, resulting in vadose zone contamination, which provides a continuous source of these contaminants to groundwater. The presence of multiple contaminants increases the complexity of finding viable remediation technologies to sequester vadose zone contaminants in situ and protect groundwater. Although previous studies have shown the efficiency of zero valent iron (ZVI) and sulfur modified iron (SMI) in reducing mobile Tc(VII) to immobile Tc(IV) and iodate incorporation into calcite, the coupled effects from simultaneously using these remedial technologies have not been previously studied. In this first-of-a-kind laboratory study, we used two efficient reductants (i.e., ZVI and SMI) and calcite-forming solutions to simultaneously remove aqueous Tc(VII) and iodate via reduction and incorporation, respectively. The results confirmed that Tc(VII) was rapidly removed from the aqueous phase via reduction to Tc(IV). ZVI removed Tc(VII) faster than SMI, although both had removed the same amount by the end of the experiments. Most of the aqueous iodate was rapidly transformed to iodide, and therefore was not incorporated into calcite, but instead remained in the aqueous phase. The iodate reduction to iodide was much faster than iodate incorporation into calcite,more » suggesting that this remedial pathway is not efficient in removing aqueous iodate when strong reductants are present. Other experiments suggested that iodate removal via calcite precipitation should occur first and then reductants should be added for Tc(VII) removal. Although ZVI can negatively impact microbial populations and thereby inhibit natural attenuation mechanisms, only changes in the makeup of the microbial community were observed. However, these changes in the microbial community may have an impact on remediation efforts in the long term that could not be seen in a short-term study. The results underscore the importance of identifying interactions between natural attenuation pathways and remediation technologies that only target individual contaminants.« less

Authors:
ORCiD logo; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1437539
Report Number(s):
PNNL-SA-129751
Journal ID: ISSN 0048-9697; 830403000
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Science of the Total Environment; Journal Volume: 636; Journal Issue: C
Country of Publication:
United States
Language:
English
Subject:
Keywords: Tc removal; groundwater remediation; nuclear waste

Citation Formats

Lawter, Amanda R., Garcia, Whitney L., Kukkadapu, Ravi K., Qafoku, Odeta, Bowden, Mark E., Saslow, Sarah A., and Qafoku, Nikolla P. Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications. United States: N. p., 2018. Web. doi:10.1016/j.scitotenv.2018.04.240.
Lawter, Amanda R., Garcia, Whitney L., Kukkadapu, Ravi K., Qafoku, Odeta, Bowden, Mark E., Saslow, Sarah A., & Qafoku, Nikolla P. Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications. United States. doi:10.1016/j.scitotenv.2018.04.240.
Lawter, Amanda R., Garcia, Whitney L., Kukkadapu, Ravi K., Qafoku, Odeta, Bowden, Mark E., Saslow, Sarah A., and Qafoku, Nikolla P. Sat . "Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications". United States. doi:10.1016/j.scitotenv.2018.04.240.
@article{osti_1437539,
title = {Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications},
author = {Lawter, Amanda R. and Garcia, Whitney L. and Kukkadapu, Ravi K. and Qafoku, Odeta and Bowden, Mark E. and Saslow, Sarah A. and Qafoku, Nikolla P.},
abstractNote = {At the Hanford Site in southeastern Washington State, radionuclide (Tc-99/I-129) laden liquid wastes have been discharged to ground, resulting in vadose zone contamination, which provides a continuous source of these contaminants to groundwater. The presence of multiple contaminants increases the complexity of finding viable remediation technologies to sequester vadose zone contaminants in situ and protect groundwater. Although previous studies have shown the efficiency of zero valent iron (ZVI) and sulfur modified iron (SMI) in reducing mobile Tc(VII) to immobile Tc(IV) and iodate incorporation into calcite, the coupled effects from simultaneously using these remedial technologies have not been previously studied. In this first-of-a-kind laboratory study, we used two efficient reductants (i.e., ZVI and SMI) and calcite-forming solutions to simultaneously remove aqueous Tc(VII) and iodate via reduction and incorporation, respectively. The results confirmed that Tc(VII) was rapidly removed from the aqueous phase via reduction to Tc(IV). ZVI removed Tc(VII) faster than SMI, although both had removed the same amount by the end of the experiments. Most of the aqueous iodate was rapidly transformed to iodide, and therefore was not incorporated into calcite, but instead remained in the aqueous phase. The iodate reduction to iodide was much faster than iodate incorporation into calcite, suggesting that this remedial pathway is not efficient in removing aqueous iodate when strong reductants are present. Other experiments suggested that iodate removal via calcite precipitation should occur first and then reductants should be added for Tc(VII) removal. Although ZVI can negatively impact microbial populations and thereby inhibit natural attenuation mechanisms, only changes in the makeup of the microbial community were observed. However, these changes in the microbial community may have an impact on remediation efforts in the long term that could not be seen in a short-term study. The results underscore the importance of identifying interactions between natural attenuation pathways and remediation technologies that only target individual contaminants.},
doi = {10.1016/j.scitotenv.2018.04.240},
journal = {Science of the Total Environment},
number = C,
volume = 636,
place = {United States},
year = {Sat Sep 01 00:00:00 EDT 2018},
month = {Sat Sep 01 00:00:00 EDT 2018}
}