Reductive sequestration of pertechnetate (99TcO4 -) by nano zerovalent iron (nZVI) transformed by abiotic sulfide

Dimin Fan, Roberto P. Anitori, Bradley Tebo, Paul Tratnyek, Juan S Lezama Pacheco, Ravi K. Kukkadapu, Mark H. Engelhard, Mark E. Bowden, Libor Kovarik, Bruce W. Arey

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Abstract

Under anoxic conditions, soluble pertechnetate (99TcO 4 -) can be reduced to less soluble TcO2· nH2O, but the oxide is highly susceptible to reoxidation. Here we investigate an alternative strategy for remediation of Tc-contaminated groundwater whereby sequestration as Tc sulfide is favored by sulfidic conditions stimulated by nano zerovalent iron (nZVI). nZVI was pre-exposed to increasing concentrations of sulfide in simulated Hanford groundwater for 24 h to mimic the onset of aquifer biotic sulfate reduction. Solid-phase characterizations of the sulfidated nZVI confirmed the formation of nanocrystalline FeS phases, but higher S/Fe ratios (>0.112) did not result in the formation of significantly more FeS. The kinetics of Tc sequestration by these materials showed faster Tc removal rates with increasing S/Fe between 0 and 0.056, but decreasing Tc removal rates with S/Fe > 0.224. The more favorable Tc removal kinetics at low S/Fe could be due to a higher affinity of TcO4 - for FeS than iron oxides, and electron microscopy confirmed that the majority of the Tc was associated with FeS phases. The inhibition of Tc removal at high S/Fe appears to have been caused by excess HS-. X-ray absorption spectroscopy revealed that as S/Fe increased, the pathway for Tc(IV) formation shifted from TcO2·nH 2O to Tc sulfide phases. The most substantial change of Tc speciation occurred at low S/Fe, coinciding with the rapid increase in Tc removal rate. This agreement further confirms the importance of FeS in Tc sequestration.

Original languageEnglish (US)
Pages (from-to)5302-5310
Number of pages9
JournalEnvironmental Science and Technology
Volume47
Issue number10
DOIs
StatePublished - May 21 2013

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Sodium Pertechnetate Tc 99m
Sulfides
Iron
sulfide
iron
Groundwater
kinetics
X ray absorption spectroscopy
Kinetics
groundwater
atomic absorption spectroscopy
electron microscopy
Remediation
Aquifers
anoxic conditions
iron oxide
Oxides
Electron microscopy
X-ray spectroscopy
Sulfates

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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Reductive sequestration of pertechnetate (99TcO4 -) by nano zerovalent iron (nZVI) transformed by abiotic sulfide. / Fan, Dimin; Anitori, Roberto P.; Tebo, Bradley; Tratnyek, Paul; Pacheco, Juan S Lezama; Kukkadapu, Ravi K.; Engelhard, Mark H.; Bowden, Mark E.; Kovarik, Libor; Arey, Bruce W.

In: Environmental Science and Technology, Vol. 47, No. 10, 21.05.2013, p. 5302-5310.

Research output: Contribution to journalArticle

Fan, D, Anitori, RP, Tebo, B, Tratnyek, P, Pacheco, JSL, Kukkadapu, RK, Engelhard, MH, Bowden, ME, Kovarik, L & Arey, BW 2013, 'Reductive sequestration of pertechnetate (99TcO4 -) by nano zerovalent iron (nZVI) transformed by abiotic sulfide', Environmental Science and Technology, vol. 47, no. 10, pp. 5302-5310. https://doi.org/10.1021/es304829z
Fan, Dimin ; Anitori, Roberto P. ; Tebo, Bradley ; Tratnyek, Paul ; Pacheco, Juan S Lezama ; Kukkadapu, Ravi K. ; Engelhard, Mark H. ; Bowden, Mark E. ; Kovarik, Libor ; Arey, Bruce W. / Reductive sequestration of pertechnetate (99TcO4 -) by nano zerovalent iron (nZVI) transformed by abiotic sulfide. In: Environmental Science and Technology. 2013 ; Vol. 47, No. 10. pp. 5302-5310.
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abstract = "Under anoxic conditions, soluble pertechnetate (99TcO 4 -) can be reduced to less soluble TcO2· nH2O, but the oxide is highly susceptible to reoxidation. Here we investigate an alternative strategy for remediation of Tc-contaminated groundwater whereby sequestration as Tc sulfide is favored by sulfidic conditions stimulated by nano zerovalent iron (nZVI). nZVI was pre-exposed to increasing concentrations of sulfide in simulated Hanford groundwater for 24 h to mimic the onset of aquifer biotic sulfate reduction. Solid-phase characterizations of the sulfidated nZVI confirmed the formation of nanocrystalline FeS phases, but higher S/Fe ratios (>0.112) did not result in the formation of significantly more FeS. The kinetics of Tc sequestration by these materials showed faster Tc removal rates with increasing S/Fe between 0 and 0.056, but decreasing Tc removal rates with S/Fe > 0.224. The more favorable Tc removal kinetics at low S/Fe could be due to a higher affinity of TcO4 - for FeS than iron oxides, and electron microscopy confirmed that the majority of the Tc was associated with FeS phases. The inhibition of Tc removal at high S/Fe appears to have been caused by excess HS-. X-ray absorption spectroscopy revealed that as S/Fe increased, the pathway for Tc(IV) formation shifted from TcO2·nH 2O to Tc sulfide phases. The most substantial change of Tc speciation occurred at low S/Fe, coinciding with the rapid increase in Tc removal rate. This agreement further confirms the importance of FeS in Tc sequestration.",
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AU - Tratnyek, Paul

AU - Pacheco, Juan S Lezama

AU - Kukkadapu, Ravi K.

AU - Engelhard, Mark H.

AU - Bowden, Mark E.

AU - Kovarik, Libor

AU - Arey, Bruce W.

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N2 - Under anoxic conditions, soluble pertechnetate (99TcO 4 -) can be reduced to less soluble TcO2· nH2O, but the oxide is highly susceptible to reoxidation. Here we investigate an alternative strategy for remediation of Tc-contaminated groundwater whereby sequestration as Tc sulfide is favored by sulfidic conditions stimulated by nano zerovalent iron (nZVI). nZVI was pre-exposed to increasing concentrations of sulfide in simulated Hanford groundwater for 24 h to mimic the onset of aquifer biotic sulfate reduction. Solid-phase characterizations of the sulfidated nZVI confirmed the formation of nanocrystalline FeS phases, but higher S/Fe ratios (>0.112) did not result in the formation of significantly more FeS. The kinetics of Tc sequestration by these materials showed faster Tc removal rates with increasing S/Fe between 0 and 0.056, but decreasing Tc removal rates with S/Fe > 0.224. The more favorable Tc removal kinetics at low S/Fe could be due to a higher affinity of TcO4 - for FeS than iron oxides, and electron microscopy confirmed that the majority of the Tc was associated with FeS phases. The inhibition of Tc removal at high S/Fe appears to have been caused by excess HS-. X-ray absorption spectroscopy revealed that as S/Fe increased, the pathway for Tc(IV) formation shifted from TcO2·nH 2O to Tc sulfide phases. The most substantial change of Tc speciation occurred at low S/Fe, coinciding with the rapid increase in Tc removal rate. This agreement further confirms the importance of FeS in Tc sequestration.

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