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Title: In situ reductive dissolution to remove Iodine-129 from aquifer sediments

Abstract

The use of an aqueous reductant (Na-dithionite) with pH buffer (K-carbonate, pH 12) was evaluated in this laboratory study as a potential remedial approach for removing Fe oxide associated iodine and enhancing pump-and-treat extraction from iodine-contaminated sediments in the unconfined aquifer in the 200 West Area of the Hanford site. X-ray fluorescence data of untreated sediment indicated that iodine was largely associated with Fe (i.e., incorporated into Fe oxides), but XANES data was inconclusive as to valence state. During groundwater leaching, aqueous and adsorbed iodine was quickly released, then additional iodine was slowly released potentially from dissolution of one or more surface phases. The Na-dithionite treatment removed greater iodine mass (2.9x) at a faster rate (1 to 4 orders of magnitude) compared to leaching with groundwater alone. Iron extractions for untreated and treated sediments showed a decrease in Fe(III)-oxides, which likely released iodine to aqueous solution. Solid phase inorganic carbon and aqueous Ca and Mg analysis further confirmed that significant calcite dissolution did not occur in these experiments meaning these phases did not release significant iodine. Although it was expected that, after treatment, 127I concentrations would eventually be lower than untreated sediments, leaching experiments showed continued, elevated iodine concentrations formore » treated samples over 750 hours. Stop flow events during 1-D column leaching suggested that some iodide precipitated within the first few pore volumes. In the survey of metals during leaching, some silver was detected which could have been solubilized by the elevated pH of initial Na-dithionite injection. Then, silver (or other metals) could have subsequently precipitated with iodide during the initial stop flow event forming a slowly dissolving source. Although significantly greater iodine is removed with treatment, the long-term leaching needs to be investigated further as it may limit dithionite treatment at the field scale.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [2]
  1. BATTELLE (PACIFIC NW LAB)
  2. Florida International University
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1599110
Report Number(s):
PNNL-SA-142245
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Environmental Radioactivity
Additional Journal Information:
Journal Volume: 216
Country of Publication:
United States
Language:
English
Subject:
iodine-129, remediation, dithionite, reductive dissolution

Citation Formats

Szecsody, James E., Emerson, Hilary P., Pearce, Carolyn I., Gartman, Brandy N., Resch, Charles T., and Di Pietro, Silvina. In situ reductive dissolution to remove Iodine-129 from aquifer sediments. United States: N. p., 2020. Web. doi:10.1016/j.jenvrad.2020.106182.
Szecsody, James E., Emerson, Hilary P., Pearce, Carolyn I., Gartman, Brandy N., Resch, Charles T., & Di Pietro, Silvina. In situ reductive dissolution to remove Iodine-129 from aquifer sediments. United States. doi:10.1016/j.jenvrad.2020.106182.
Szecsody, James E., Emerson, Hilary P., Pearce, Carolyn I., Gartman, Brandy N., Resch, Charles T., and Di Pietro, Silvina. Fri . "In situ reductive dissolution to remove Iodine-129 from aquifer sediments". United States. doi:10.1016/j.jenvrad.2020.106182.
@article{osti_1599110,
title = {In situ reductive dissolution to remove Iodine-129 from aquifer sediments},
author = {Szecsody, James E. and Emerson, Hilary P. and Pearce, Carolyn I. and Gartman, Brandy N. and Resch, Charles T. and Di Pietro, Silvina},
abstractNote = {The use of an aqueous reductant (Na-dithionite) with pH buffer (K-carbonate, pH 12) was evaluated in this laboratory study as a potential remedial approach for removing Fe oxide associated iodine and enhancing pump-and-treat extraction from iodine-contaminated sediments in the unconfined aquifer in the 200 West Area of the Hanford site. X-ray fluorescence data of untreated sediment indicated that iodine was largely associated with Fe (i.e., incorporated into Fe oxides), but XANES data was inconclusive as to valence state. During groundwater leaching, aqueous and adsorbed iodine was quickly released, then additional iodine was slowly released potentially from dissolution of one or more surface phases. The Na-dithionite treatment removed greater iodine mass (2.9x) at a faster rate (1 to 4 orders of magnitude) compared to leaching with groundwater alone. Iron extractions for untreated and treated sediments showed a decrease in Fe(III)-oxides, which likely released iodine to aqueous solution. Solid phase inorganic carbon and aqueous Ca and Mg analysis further confirmed that significant calcite dissolution did not occur in these experiments meaning these phases did not release significant iodine. Although it was expected that, after treatment, 127I concentrations would eventually be lower than untreated sediments, leaching experiments showed continued, elevated iodine concentrations for treated samples over 750 hours. Stop flow events during 1-D column leaching suggested that some iodide precipitated within the first few pore volumes. In the survey of metals during leaching, some silver was detected which could have been solubilized by the elevated pH of initial Na-dithionite injection. Then, silver (or other metals) could have subsequently precipitated with iodide during the initial stop flow event forming a slowly dissolving source. Although significantly greater iodine is removed with treatment, the long-term leaching needs to be investigated further as it may limit dithionite treatment at the field scale.},
doi = {10.1016/j.jenvrad.2020.106182},
journal = {Journal of Environmental Radioactivity},
number = ,
volume = 216,
place = {United States},
year = {2020},
month = {5}
}