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Title: Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite

Abstract

99Tc is formed mostly during nuclear reactions and is released into the environment during weapons testing and inadvertent waste disposal. The long half-life, high environmental mobility (as Tc(VII)O4-) and its possible uptake into the food chain cause 99Tc to be a significant environmental contaminant. In this study, we evaluated the role of Fe(II) in biologically reduced clay mineral, nontronite (NAu-2), in reducing Tc(VII)O4- to poorly soluble Tc(IV) species as a function of pH and Fe(II) concentration. The rate of Tc(VII) reduction by Fe(II) in NAu-2 was higher at neutral pH (pH 7.0) than at acidic and basic pHs when Fe(II) concentration was low (< 1 mmol/g). The effect of pH, however, was insignificant at higher Fe(II) concentrations. The reduction of Tc(VII) by Fe(II) associated with NAu-2 was also studied in the presence of common subsurface oxidants including iron and manganese oxides, nitrate, and oxygen, to evaluate the effect of the oxidants on the enhancement and inhibition of Tc(VII) reduction, and reoxidation of Tc(IV). Addition of iron oxides (goethite and hematite) to the Tc(VII)-NAu-2 system, where Tc(VII) reduction was ongoing, enhanced reduction of Tc(VII), apparently as a result of re-distribution of reactive Fe(II) from NAu-2 to more reactive goethite/hematite surfaces. Additionmore » of manganese oxides stopped further Tc(VII) reduction, and in case of K+-birnessite, it reoxidized previously reduced Tc(IV). Nitrate neither enhanced reduction of Tc(VII) nor promoted reoxidation of Tc(IV). Approximately 11% of Tc(IV) was oxidized by oxygen. The rate and extent of Tc(IV) reoxidation was found to strongly depend on the nature of the oxidants and concentration of Fe(II). When the same oxidants were added to aged Tc reduction products (mainly NAu-2 and TcO2•nH2O), the extent of Tc(IV) reoxidation decreased significantly relative to fresh Tc(IV) products. Increasing NAu-2 concentration also resulted in the decreased extent of Tc(IV) reoxidation. The results were attributed to the effect of NAu-2 aggregation that effectively retained Tc(IV) in the solid and decreased its vulnerability to reoxidation. Overall, our results implied that bioreduced clay minerals could play an important role in reducing Tc(VII) and in maintaining the long-term stability of reduced Tc(IV).« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
953361
Report Number(s):
PNNL-SA-65652
Journal ID: ISSN 0009-2541; CHGEAD; KP1504010; TRN: US0902751
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Chemical Geology, 264(1-4):127-138
Additional Journal Information:
Journal Volume: 264; Journal Issue: 1-4; Journal ID: ISSN 0009-2541
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CLAYS; FOOD CHAINS; GOETHITE; HEMATITE; IRON; IRON OXIDES; MANGANESE OXIDES; NITRATES; NUCLEAR REACTIONS; OXIDIZERS; OXYGEN; STABILITY; TECHNETIUM; TESTING; VULNERABILITY; WASTE DISPOSAL; WEAPONS; iron; microbial; nontronite; reduction; reoxidation; technetium

Citation Formats

Jaisi, Deb P, Dong, Hailiang, Plymale, Andrew E, Fredrickson, Jim K, Zachara, John M, Heald, S, and Liu, Chongxuan. Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite. United States: N. p., 2009. Web. doi:10.1016/j.chemgeo.2009.02.018.
Jaisi, Deb P, Dong, Hailiang, Plymale, Andrew E, Fredrickson, Jim K, Zachara, John M, Heald, S, & Liu, Chongxuan. Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite. United States. https://doi.org/10.1016/j.chemgeo.2009.02.018
Jaisi, Deb P, Dong, Hailiang, Plymale, Andrew E, Fredrickson, Jim K, Zachara, John M, Heald, S, and Liu, Chongxuan. Sat . "Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite". United States. https://doi.org/10.1016/j.chemgeo.2009.02.018.
@article{osti_953361,
title = {Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite},
author = {Jaisi, Deb P and Dong, Hailiang and Plymale, Andrew E and Fredrickson, Jim K and Zachara, John M and Heald, S and Liu, Chongxuan},
abstractNote = {99Tc is formed mostly during nuclear reactions and is released into the environment during weapons testing and inadvertent waste disposal. The long half-life, high environmental mobility (as Tc(VII)O4-) and its possible uptake into the food chain cause 99Tc to be a significant environmental contaminant. In this study, we evaluated the role of Fe(II) in biologically reduced clay mineral, nontronite (NAu-2), in reducing Tc(VII)O4- to poorly soluble Tc(IV) species as a function of pH and Fe(II) concentration. The rate of Tc(VII) reduction by Fe(II) in NAu-2 was higher at neutral pH (pH 7.0) than at acidic and basic pHs when Fe(II) concentration was low (< 1 mmol/g). The effect of pH, however, was insignificant at higher Fe(II) concentrations. The reduction of Tc(VII) by Fe(II) associated with NAu-2 was also studied in the presence of common subsurface oxidants including iron and manganese oxides, nitrate, and oxygen, to evaluate the effect of the oxidants on the enhancement and inhibition of Tc(VII) reduction, and reoxidation of Tc(IV). Addition of iron oxides (goethite and hematite) to the Tc(VII)-NAu-2 system, where Tc(VII) reduction was ongoing, enhanced reduction of Tc(VII), apparently as a result of re-distribution of reactive Fe(II) from NAu-2 to more reactive goethite/hematite surfaces. Addition of manganese oxides stopped further Tc(VII) reduction, and in case of K+-birnessite, it reoxidized previously reduced Tc(IV). Nitrate neither enhanced reduction of Tc(VII) nor promoted reoxidation of Tc(IV). Approximately 11% of Tc(IV) was oxidized by oxygen. The rate and extent of Tc(IV) reoxidation was found to strongly depend on the nature of the oxidants and concentration of Fe(II). When the same oxidants were added to aged Tc reduction products (mainly NAu-2 and TcO2•nH2O), the extent of Tc(IV) reoxidation decreased significantly relative to fresh Tc(IV) products. Increasing NAu-2 concentration also resulted in the decreased extent of Tc(IV) reoxidation. The results were attributed to the effect of NAu-2 aggregation that effectively retained Tc(IV) in the solid and decreased its vulnerability to reoxidation. Overall, our results implied that bioreduced clay minerals could play an important role in reducing Tc(VII) and in maintaining the long-term stability of reduced Tc(IV).},
doi = {10.1016/j.chemgeo.2009.02.018},
url = {https://www.osti.gov/biblio/953361}, journal = {Chemical Geology, 264(1-4):127-138},
issn = {0009-2541},
number = 1-4,
volume = 264,
place = {United States},
year = {2009},
month = {6}
}