Oxidation of H2S by Iron Oxides in Unsaturated Conditions

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• 作者：Kirk J. Cantrell ; Steven B. Yabusaki ; Mark H. Engelhard ; Alexandre V. Mitroshkov ; and Edward C. Thornton
• 刊名：Environmental Science & Technology
• 出版年：2003
• 出版时间：May 15, 2003
• 年：2003
• 卷：37
• 期：10
• 页码：2192 - 2199
• 全文大小：217K
• 年卷期：v.37,no.10(May 15, 2003)
• ISSN：1520-5851

文摘

Previous studies have demonstrated that gas-phase H₂Scan immobilize certain redox-sensitive contaminants (e.g.,Cr, U, Tc) in vadose zone environments. A key issue foreffective and efficient delivery of H₂S in these environmentsis the reactivity of the gas with indigenous iron oxides.To elucidate the factors that control the transport of H₂Sin the vadose zone, laboratory column experiments wereconducted to identify reaction mechanisms and measurerates of H₂S oxidation by iron oxide-coated sands using severalcarrier gas compositions (N₂, air, and O₂) and flow rates.Most experiments were conducted using ferrihydrite-coatedsand. Additional studies were conducted with goethite-and hematite-coated sand and a natural sediment. Selectiveextractions were conducted at the end of each columnexperiment to determine the mass balance of the reactionproducts. XPS was used to confirm the presence of thereaction products. For column experiments in whichferrihydrite-coated sand was the substrate and N₂ wasthe carrier gas, the major H₂S oxidation products were FeSand elemental sulfur (mostly S₈⁰, represented as S⁰ forsimplicity) at ratios that were consistent with the stoichiometryof the postulated reactions. When air or O₂ were usedas the carrier gas, S⁰ became the dominant reaction productalong with FeS₂ and smaller amounts of FeS, sulfate,and thiosulfate. A mathematical model of reactive transportwas used to test the hypothesis that S⁰ forming on theiron oxide surfaces reduces access of H₂S to the reactivesurface. Several conceptual models were assessed inthe context of the postulated reactions with the final modelbased on a linear surface poisoning model and fittedreaction rates. These results indicate that carrier gasselection is a critical consideration with significant tradeoffsfor remediation objectives.