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 nanozerovalent iron (nZVI). Tc sequestration pathways along the development of sulfate reduction were examined by using incremental abiotic sulfide to mimic the onset of aquifer biotic sulfate reduction. The kinetics of Tc sequestration showed faster Tc removal rates when S/Fe increased from 0 to 0.056, but decreasing Tc removal rates with S/Fe > 0.224. Electron microscopy confirmed that the majority of the Tc was associated with FeS phases. X-ray absorption spectroscopy revealed that as S/Fe increased, the pathway for Tc(IV) formation 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. At high S/Fe, excess aqueous sulfide was present, likely to cause the inhibition of Tc sequestration. The reoxidation kinetics of Tc sequestered under sulfidic conditions was significantly slower than that under non-sulfidic conditions, indicating that Tc(IV) sulfide is more resistant to oxidation than Tc(IV) oxide.

Reductive sequestration of pertechnetate (99TcO4�) as Tc(VI) sulfide under sulfidogenesis stimulated by nanozerovalent iron (nZVI) and limited remobilization

246th National Meeting (2013)

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