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Title: Iodine speciation in a silver-amended cementitious system

Abstract

Silver-impregnated zeolite (AgIZ) has been used for removing radioiodine from contaminated groundwater and nuclear waste streams and the worldwide inventory of such secondary waste is rapidly increasing. The objective of this work was to 1) quantify the effectiveness of two grout waste forms for disposing of the used AgIZ, and 2) determine the I speciation leached from AgIZ encapsulated in grout. A 60-day kinetics batch experiment demonstrated that AgIZ encapsulated in slag-free grout was extremely effective at immobilizing I and Ag, a potential non-radioactive carcinogen. However, AgIZ encapsulated in slag-containing grout, the most common type of grout used for low-level radioactive waste disposal, was entirely ineffective at immobilizing I. While the slagfree grout with AgIZ released only 3.3 μg/L I total into the contact solution, the slag-containing grout released 19,269 μg/L I total. Based on thermodynamic calculations, the strongly reducing conditions of the slag-containing system (Eh was –392 mV) promoted the reductive dissolution of the AgI, forming Ag 0 (aq) and releasing iodide (I ) into the aqueous phase. The slag-free grout system was maintained under more oxidizing conditions (Eh was 439 mV) and a minimal amount of I was released from the grout. In both grout systems, the aqueousmore » I, originally added to the AgZ as iodide, was composed primarily of iodide and org-I, and essentially no iodate was detected. More organo-I was detected in the slag-free than the slag-containing grout system because the high redox potential of the former system was more conducive to the formation of oxidized I species, such as I 2, which may be intermediates in the covalent bonding of I with organic C in grout. Iodine K-edge XANES analysis suggested that I existed exclusively as silver iodide in both AgIZ-grout samples. Together, these results indicate that subsurface grout disposal of AgIZ waste should be done under oxidizing conditions and that radioiodide released from AgIZ can undergo speciation transformations that have important implications on subsequent mobility and estimated risk.« less

Authors:
 [1];  [2];  [3];  [1];  [3];  [3];  [1];  [3];  [2];  [4];  [5];  [3]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
  2. Univ. of Georgia, Aiken, SC (United States)
  3. Texas A&M Univ., Galveston, TX (United States)
  4. Tokyo Inst. of Technology (Japan)
  5. Canadian Light Sources, Inc., Saskatoon, SK (Canada)
Publication Date:
Research Org.:
Univ. of Georgia, Athens, GA (United States); Texas A&M Univ., Galveston, TX (United States)
Sponsoring Org.:
USDOE Office of Science (SC); USDOE Office of Environmental Management (EM)
OSTI Identifier:
1547652
Alternate Identifier(s):
OSTI ID: 1547365
Grant/Contract Number:  
FC09-07SR22506; EM0004381; LDRD-2017-00005; DEFC09-07-SR22506
Resource Type:
Published Article
Journal Name:
Environment International
Additional Journal Information:
Journal Volume: 126; Journal Issue: C; Journal ID: ISSN 0160-4120
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
Iodine speciation; cement; slag; immobilization; redox; silver-impregnated zeolite

Citation Formats

Kaplan, Daniel I., Price, Kimberly A., Xu, Chen, Li, Dien, Lin, Peng, Xing, Wei, Nichols, Ralph, Schwehr, Kathleen, Seaman, John C., Ohnuki, Toshihiko, Chen, Ning, and Santschi, Peter H. Iodine speciation in a silver-amended cementitious system. United States: N. p., 2019. Web. doi:10.1016/j.envint.2019.02.070.
Kaplan, Daniel I., Price, Kimberly A., Xu, Chen, Li, Dien, Lin, Peng, Xing, Wei, Nichols, Ralph, Schwehr, Kathleen, Seaman, John C., Ohnuki, Toshihiko, Chen, Ning, & Santschi, Peter H. Iodine speciation in a silver-amended cementitious system. United States. doi:10.1016/j.envint.2019.02.070.
Kaplan, Daniel I., Price, Kimberly A., Xu, Chen, Li, Dien, Lin, Peng, Xing, Wei, Nichols, Ralph, Schwehr, Kathleen, Seaman, John C., Ohnuki, Toshihiko, Chen, Ning, and Santschi, Peter H. Fri . "Iodine speciation in a silver-amended cementitious system". United States. doi:10.1016/j.envint.2019.02.070.
@article{osti_1547652,
title = {Iodine speciation in a silver-amended cementitious system},
author = {Kaplan, Daniel I. and Price, Kimberly A. and Xu, Chen and Li, Dien and Lin, Peng and Xing, Wei and Nichols, Ralph and Schwehr, Kathleen and Seaman, John C. and Ohnuki, Toshihiko and Chen, Ning and Santschi, Peter H.},
abstractNote = {Silver-impregnated zeolite (AgIZ) has been used for removing radioiodine from contaminated groundwater and nuclear waste streams and the worldwide inventory of such secondary waste is rapidly increasing. The objective of this work was to 1) quantify the effectiveness of two grout waste forms for disposing of the used AgIZ, and 2) determine the I speciation leached from AgIZ encapsulated in grout. A 60-day kinetics batch experiment demonstrated that AgIZ encapsulated in slag-free grout was extremely effective at immobilizing I and Ag, a potential non-radioactive carcinogen. However, AgIZ encapsulated in slag-containing grout, the most common type of grout used for low-level radioactive waste disposal, was entirely ineffective at immobilizing I. While the slagfree grout with AgIZ released only 3.3 μg/L Itotal into the contact solution, the slag-containing grout released 19,269 μg/L Itotal. Based on thermodynamic calculations, the strongly reducing conditions of the slag-containing system (Eh was –392 mV) promoted the reductive dissolution of the AgI, forming Ag0(aq) and releasing iodide (I–) into the aqueous phase. The slag-free grout system was maintained under more oxidizing conditions (Eh was 439 mV) and a minimal amount of I was released from the grout. In both grout systems, the aqueous I, originally added to the AgZ as iodide, was composed primarily of iodide and org-I, and essentially no iodate was detected. More organo-I was detected in the slag-free than the slag-containing grout system because the high redox potential of the former system was more conducive to the formation of oxidized I species, such as I2, which may be intermediates in the covalent bonding of I with organic C in grout. Iodine K-edge XANES analysis suggested that I existed exclusively as silver iodide in both AgIZ-grout samples. Together, these results indicate that subsurface grout disposal of AgIZ waste should be done under oxidizing conditions and that radioiodide released from AgIZ can undergo speciation transformations that have important implications on subsequent mobility and estimated risk.},
doi = {10.1016/j.envint.2019.02.070},
journal = {Environment International},
number = C,
volume = 126,
place = {United States},
year = {2019},
month = {3}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1016/j.envint.2019.02.070

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