skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium

Abstract

In situ technetium-99 (99Tc) immobilization by Fe(II) associated with clay minerals has been studied and is a potential cost-effective method for Tc remediation at the United States Department of Energy (DOE) sites. Fe redox cycling are common in sedimentary environments, however their effect on Tc reduction and immobilization has not yet been investigated. The objective of this project was therefore to study how multiple cycles of reduction-reoxidation of Fe-rich clay mineral, nontronite, affected its reactivity toward Tc (VII) reduction. Iron-rich nontronite NAu-2 was used as a model clay mineral. NAu-2 suspension was first bioreduced by Shewanella putrefaciens CN32, which consequently was re-oxidized by air. Three cycles of reduction-oxidation were conducted and bioreduced NAu-2 samples from all three cycles were collected and used for Tc(VII) reduction experiments. Each redox cycle resulted in a small fraction of dissolution of small size and/or poorly crystalline NAu-2. The released Fe(II) from the dissolution was likely adsorbed onto NAu-2 surface/edge sites with a high reactivity. Upon exposure to O2, this reactive Fe(II) fraction was oxidized more rapidly than structural Fe(II) and may have accounted for a two-step reoxidation kinetics of NAu-2 associated Fe(II): rapid oxidation over first few hours followed by slow oxidation. Progressive increasemore » of this reactive fraction of Fe(II), from increased dissolution, accounted for the successively higher rate of bioreduction and reoxidation with increased redox cycles. The same Fe redistribution accounted for two-step Tc(VII) reduction kinetics as well. Rapid Tc(VII) reduction in the first few hours may be attributed to a small fraction of highly reactive Fe(II) at the NAu-2 surface/edge sites, and more steady Tc(VII) reduction over longer time may be carried out by structural Fe(II). Similar to the increased rates of Fe(III) reduction and Fe(II) oxidation, the Tc(VII) reduction rate also increased with redox cycles and could be explained by progressive increase of the reactive Fe(II) on NAu-2 surface/edges. These results suggest that iron-rich clay minerals undergo important changes after redox cycles, but eventually reach a steady state with continued reactivity toward heavy metals.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1033452
Report Number(s):
PNNL-SA-79180
Journal ID: ISSN 0009-2541; CHGEAD; 25610; 41590; 44687; KP1704020; TRN: US1200331
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Chemical Geology, 291:206-216
Additional Journal Information:
Journal Volume: 291; Journal ID: ISSN 0009-2541
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 74 ATOMIC AND MOLECULAR PHYSICS; AIR; CLAYS; DISSOLUTION; HEAVY METALS; IRON; KINETICS; OXIDATION; TECHNETIUM; TECHNETIUM 99; Effects; Redox; Cycling; Iron; Nontronite; Reduction; Technetium; Environmental Molecular Sciences Laboratory

Citation Formats

Yang, Junjie, Kukkadapu, Ravi K, Dong, Hailiang, Shelobolina, Evgenya S, Zhang, Jing, and Kim, Jinwook. Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium. United States: N. p., 2012. Web. doi:10.1016/j.chemgeo.2011.10.013.
Yang, Junjie, Kukkadapu, Ravi K, Dong, Hailiang, Shelobolina, Evgenya S, Zhang, Jing, & Kim, Jinwook. Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium. United States. https://doi.org/10.1016/j.chemgeo.2011.10.013
Yang, Junjie, Kukkadapu, Ravi K, Dong, Hailiang, Shelobolina, Evgenya S, Zhang, Jing, and Kim, Jinwook. Fri . "Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium". United States. https://doi.org/10.1016/j.chemgeo.2011.10.013.
@article{osti_1033452,
title = {Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium},
author = {Yang, Junjie and Kukkadapu, Ravi K and Dong, Hailiang and Shelobolina, Evgenya S and Zhang, Jing and Kim, Jinwook},
abstractNote = {In situ technetium-99 (99Tc) immobilization by Fe(II) associated with clay minerals has been studied and is a potential cost-effective method for Tc remediation at the United States Department of Energy (DOE) sites. Fe redox cycling are common in sedimentary environments, however their effect on Tc reduction and immobilization has not yet been investigated. The objective of this project was therefore to study how multiple cycles of reduction-reoxidation of Fe-rich clay mineral, nontronite, affected its reactivity toward Tc (VII) reduction. Iron-rich nontronite NAu-2 was used as a model clay mineral. NAu-2 suspension was first bioreduced by Shewanella putrefaciens CN32, which consequently was re-oxidized by air. Three cycles of reduction-oxidation were conducted and bioreduced NAu-2 samples from all three cycles were collected and used for Tc(VII) reduction experiments. Each redox cycle resulted in a small fraction of dissolution of small size and/or poorly crystalline NAu-2. The released Fe(II) from the dissolution was likely adsorbed onto NAu-2 surface/edge sites with a high reactivity. Upon exposure to O2, this reactive Fe(II) fraction was oxidized more rapidly than structural Fe(II) and may have accounted for a two-step reoxidation kinetics of NAu-2 associated Fe(II): rapid oxidation over first few hours followed by slow oxidation. Progressive increase of this reactive fraction of Fe(II), from increased dissolution, accounted for the successively higher rate of bioreduction and reoxidation with increased redox cycles. The same Fe redistribution accounted for two-step Tc(VII) reduction kinetics as well. Rapid Tc(VII) reduction in the first few hours may be attributed to a small fraction of highly reactive Fe(II) at the NAu-2 surface/edge sites, and more steady Tc(VII) reduction over longer time may be carried out by structural Fe(II). Similar to the increased rates of Fe(III) reduction and Fe(II) oxidation, the Tc(VII) reduction rate also increased with redox cycles and could be explained by progressive increase of the reactive Fe(II) on NAu-2 surface/edges. These results suggest that iron-rich clay minerals undergo important changes after redox cycles, but eventually reach a steady state with continued reactivity toward heavy metals.},
doi = {10.1016/j.chemgeo.2011.10.013},
url = {https://www.osti.gov/biblio/1033452}, journal = {Chemical Geology, 291:206-216},
issn = {0009-2541},
number = ,
volume = 291,
place = {United States},
year = {2012},
month = {1}
}