Oxidative Remobilization of Technetium Sequestered by Sulfide-Transformed Nano Zerovalent Iron

详细信息    查看全文

• 作者：Dimin Fan ; Roberto P. Anitori ; Bradley M. Tebo ; Paul G. Tratnyek ; Juan S. Lezama Pacheco ; Ravi K. Kukkadapu ; Libor Kovarik ; Mark H. Engelhard ; Mark E. Bowden
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：July 1, 2014
• 年：2014
• 卷：48
• 期：13
• 页码：7409-7417
• 全文大小：447K
• ISSN：1520-5851

文摘

Our previous study showed that formation of TcS₂-like phases is favored over TcO₂ under sulfidic conditions stimulated by nano zerovalent iron. This study further investigates the stability of Tc(IV) sulfide upon reoxidation by solution chemistry, solid phase characterization, and X-ray absorption spectroscopy. Tc dissolution data showed that Tc(VII) reduced by sulfide-transformed nZVI has substantially slower reoxidation kinetics than Tc(VII) reduced by nZVI only. The initial inhibition of Tc(IV) dissolution at S/Fe = 0.112 is due to the redox buffer capacity of FeS, which is evidenced by the parallel trends in oxidation鈥搑eduction potentials (ORP) and Tc dissolution kinetics. The role of FeS in inhibiting Tc oxidation is further supported by the M枚ssbauer spectroscopy and micro X-ray diffraction data at S/Fe = 0.112, showing persistence of FeS after 24-h oxidation but complete oxidation after 120-h oxidation. X-ray absorption spectroscopy data for S/Fe = 0.011 showed significantly increasing percentages of TcS₂ in the solid phase after 24-h oxidation, indicating stronger resistance of TcS₂ to oxidation. At S/Fe = 0.112, the XAS results revealed significant transformation of Tc speciation from TcS₂ to TcO₂ after 120-h oxidation. Given that no apparent Tc dissolution occurred during this period, the speciation transformation might play a secondary role in hindering Tc oxidation. Collectively, the results indicate that sequestrating Tc as TcS₂ under stimulated sulfate reduction is a promising strategy to improve the long-term stability of reduced Tc in subsurface remediation.