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Title: Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99)

Abstract

99Technetium (99Tc) is a fission product of uranium-235 and plutonium-239 and poses a high environmental hazard due to its long half-life (t1/2 = 2.13 x 105 y), abundance in nuclear wastes, and environmental mobility under oxidizing conditions [i.e., Tc(VII)]. Under reducing conditions, Tc(VII) can be reduced to insoluble Tc(IV). Ferrous iron [Fe(II)], either in aqueous form or in mineral form, has been used to reduce Tc(VII) to Tc(IV). However, the reactivity of Fe(II) from clay minerals, other than nontronite, toward immobilization of Tc(VII) and its role in retention of reduced Tc(IV) have not been investigated. In this study the reactivity of a suite of clay minerals toward Tc(VII) reduction and immobilization was evaluated. The clay minerals chosen for this study included five members in the smectite-illite (S-I) series, (montmorillonite, nontronite, rectorite, mixed layered I-S, and illite), chlorite, and palygorskite. Fe-oxides were removed from these minerals with a modified dithionite-citrate-bicarbonate (DCB) procedure. The total Fe content of these clay minerals, after Fe-oxide removal, ranged from 0.7 to 30.4% by weight, and the Fe(III)/Fe(total) ratio ranged from 44.9 to 98.5%. X-ray diffraction (XRD) and Mössbauer spectroscopy results showed that after Fe oxide removal the clay minerals were free of Fe-oxides. Scanning electronmore » microscopy (SEM) revealed that little dissolution occurred during the DCB treatment. Bioreduction experiments were performed in bicarbonate buffer (pH-7) with Fe(III) in the clay minerals as the sole electron acceptor, lactate as the sole electron donor, and Shewanella Putrifaciens CN32 cells as mediators. In select tubes, anthraquinone-2,6-disulfate (AQDS) was added as electron shuttle to facilitate electron transfer. The extent of Fe(III) bioreduction was the highest for chlorite (~43 wt%) and the lowest for palygorskite (~4.17 wt%). In the S-I series, NAu-2 was the most reducible (~31 %) and illite the least (~0.4 %). The extent and initial rate of bioreduction were positively correlated with the percent smectite in the S-I series (i.e., layer expandability). Fe(II) in the bioreduced clay minerals subsequently was used to reduce Tc(VII) to Tc(IV) in PIPES buffer. Similar to the trend of bioreduction, in the S-I series, reduced smectite showed the highest reactivity toward Tc(VII), and reduced illite exhibited the least. The initial rate of Tc(VII) reduction, after normalization to clay and Fe(II) concentrations, was positively correlated with the percent smectite in the S-I series. Fe(II) in chlorite and palygorskite was also reactive toward Tc(VII) reduction. These data demonstrate that crystal chemical parameters (layer expandability, Fe and Fe(II) contents, and surface area etc.) play important roles in controlling the extent and rate of bioreduction and the reactivity toward Tc(VII) reduction. Reduced Tc(IV) resides within clay mineral matrix, and this association could minimize any potential of reoxidation over long term.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1022420
Report Number(s):
PNNL-SA-77983
Journal ID: ISSN 0016-7037; GCACAK; 25610; KP1704020; TRN: US1104175
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta, 75(18):5229-5246
Additional Journal Information:
Journal Volume: 75; Journal Issue: 18; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ACID CARBONATES; BINDING ENERGY; CHLORINE COMPOUNDS; CLAYS; ELECTRON TRANSFER; FISSION PRODUCTS; ILLITE; OXYGEN COMPOUNDS; PERTECHNETATES; PLUTONIUM 239; RADIOACTIVE WASTES; SCANNING ELECTRON MICROSCOPY; SMECTITE; SURFACE AREA; URANIUM 235; X-RAY DIFFRACTION; bioreduction; chlorite; ripidolite; illite; montmorillonite; nontronite; palygorskite; rectorite; Shewanella; Putrifaciens; CN32; smectite; Tc(VII); reduction; Environmental Molecular Sciences Laboratory

Citation Formats

Bishop, Michael E, Dong, Hailiang, Kukkadapu, Ravi K, Liu, Chongxuan, and Edelmann, Richard E. Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99). United States: N. p., 2011. Web. doi:10.1016/j.gca.2011.06.034.
Bishop, Michael E, Dong, Hailiang, Kukkadapu, Ravi K, Liu, Chongxuan, & Edelmann, Richard E. Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99). United States. https://doi.org/10.1016/j.gca.2011.06.034
Bishop, Michael E, Dong, Hailiang, Kukkadapu, Ravi K, Liu, Chongxuan, and Edelmann, Richard E. Fri . "Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99)". United States. https://doi.org/10.1016/j.gca.2011.06.034.
@article{osti_1022420,
title = {Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99)},
author = {Bishop, Michael E and Dong, Hailiang and Kukkadapu, Ravi K and Liu, Chongxuan and Edelmann, Richard E},
abstractNote = {99Technetium (99Tc) is a fission product of uranium-235 and plutonium-239 and poses a high environmental hazard due to its long half-life (t1/2 = 2.13 x 105 y), abundance in nuclear wastes, and environmental mobility under oxidizing conditions [i.e., Tc(VII)]. Under reducing conditions, Tc(VII) can be reduced to insoluble Tc(IV). Ferrous iron [Fe(II)], either in aqueous form or in mineral form, has been used to reduce Tc(VII) to Tc(IV). However, the reactivity of Fe(II) from clay minerals, other than nontronite, toward immobilization of Tc(VII) and its role in retention of reduced Tc(IV) have not been investigated. In this study the reactivity of a suite of clay minerals toward Tc(VII) reduction and immobilization was evaluated. The clay minerals chosen for this study included five members in the smectite-illite (S-I) series, (montmorillonite, nontronite, rectorite, mixed layered I-S, and illite), chlorite, and palygorskite. Fe-oxides were removed from these minerals with a modified dithionite-citrate-bicarbonate (DCB) procedure. The total Fe content of these clay minerals, after Fe-oxide removal, ranged from 0.7 to 30.4% by weight, and the Fe(III)/Fe(total) ratio ranged from 44.9 to 98.5%. X-ray diffraction (XRD) and Mössbauer spectroscopy results showed that after Fe oxide removal the clay minerals were free of Fe-oxides. Scanning electron microscopy (SEM) revealed that little dissolution occurred during the DCB treatment. Bioreduction experiments were performed in bicarbonate buffer (pH-7) with Fe(III) in the clay minerals as the sole electron acceptor, lactate as the sole electron donor, and Shewanella Putrifaciens CN32 cells as mediators. In select tubes, anthraquinone-2,6-disulfate (AQDS) was added as electron shuttle to facilitate electron transfer. The extent of Fe(III) bioreduction was the highest for chlorite (~43 wt%) and the lowest for palygorskite (~4.17 wt%). In the S-I series, NAu-2 was the most reducible (~31 %) and illite the least (~0.4 %). The extent and initial rate of bioreduction were positively correlated with the percent smectite in the S-I series (i.e., layer expandability). Fe(II) in the bioreduced clay minerals subsequently was used to reduce Tc(VII) to Tc(IV) in PIPES buffer. Similar to the trend of bioreduction, in the S-I series, reduced smectite showed the highest reactivity toward Tc(VII), and reduced illite exhibited the least. The initial rate of Tc(VII) reduction, after normalization to clay and Fe(II) concentrations, was positively correlated with the percent smectite in the S-I series. Fe(II) in chlorite and palygorskite was also reactive toward Tc(VII) reduction. These data demonstrate that crystal chemical parameters (layer expandability, Fe and Fe(II) contents, and surface area etc.) play important roles in controlling the extent and rate of bioreduction and the reactivity toward Tc(VII) reduction. Reduced Tc(IV) resides within clay mineral matrix, and this association could minimize any potential of reoxidation over long term.},
doi = {10.1016/j.gca.2011.06.034},
url = {https://www.osti.gov/biblio/1022420}, journal = {Geochimica et Cosmochimica Acta, 75(18):5229-5246},
issn = {0016-7037},
number = 18,
volume = 75,
place = {United States},
year = {2011},
month = {7}
}