New Paper: Sequestration of Technetium with Sulfidated Zerovalent Iron

[PGT]

This is the first part of our study of technetium immobilization as technetium sulfide but stimulation of sulfidogenic conditions by adding zerovalent iron. It concerns the reduction kinetics and products. The next paper will address reoxidation back to soluble pertechnetate.

For those of you who do not have subscriber access to this journal, the following link is supposed to provide 50 free e-prints (PDFs):

http://pubs.acs.org/articlesonrequest/AOR-zNXJvFgAyeX2SxQ9axfu

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Fan, D., R. P. Anitori, B. M. Tebo, P. G. Tratnyek, J. S. Lezama Pacheco, R. K. Kukkadapu, M. H. Engelhard, M. E. Bowden, L. Kovarik, and B. W. Arey. 2013. Reductive sequestration of pertechnetate (⁹⁹TcO₄^–) by nano zero-valent iron (nZVI) transformed by abiotic sulfide. Environ. Sci. Technol.: ASAP.

Under anoxic conditions, soluble 99TcO4– 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 zero-valent iron (nZVI). nZVI was pre-exposed to increasing concentrations of sulfide in simulated Hanford groundwater for 24 hrs to mimic the stages of aquifer sulfate reduction and onset of biotic sulfidogenesis. 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 S/Fe = 0–0.056, 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, Tc speciation shifted from TcO2•nH2O to TcS2. 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.

DOI: http://dx.doi.org/10.1021/es304829z