Reoxidation Behavior of Technetium, Iron, and Sulfur in Estuarine Sediments

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• 作者：Ian T. Burke ; Christopher Boothman ; Jonathan R. Lloyd ; Francis R. Livens ; John M. Charnock ; Joyce M. McBeth ; Robert J. G. Mortimer ; and Katherine Morris
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：June 1, 2006
• 年：2006
• 卷：40
• 期：11
• 页码：3529 - 3535
• 全文大小：140K
• 年卷期：v.40,no.11(June 1, 2006)
• ISSN：1520-5851

文摘

Technetium is a redox active radionuclide, which ispresent as a contaminant at a number of sites wherenuclear fuel cycle operations have been carried out. Recentstudies suggest that Tc(VII), which is soluble under oxicconditions, will be retained in sediments as Fe(III)-reducingconditions develop, due to reductive scavenging ashydrous TcO₂. However, the behavior of technetium duringsubsequent reoxidation of sediments remains poorlycharacterized. Here, we describe a microcosm-basedapproach to investigate the reoxidation behavior of reduced,technetium-contaminated sediments. In reoxidationexperiments, the behavior of Tc was strongly dependenton the nature of the oxidant. With air, reoxidation of Fe(II)and, in sulfate-reducing sediments, sulfide occurredaccompanied by ~50% remobilization of Tc to solution asTcO₄^-. With nitrate, reoxidation of Fe(II) and, in sulfate-reducing sediments, sulfide only occurred in microbiallyactive experiments where Fe(II) and sulfide oxidation coupledto nitrate reduction was occurring. Here, Tc wasrecalcitrant to remobilization with <10% Tc remobilized tosolution even when extensive Fe(II) and sulfide reoxidationhad occurred. X-ray absorption spectroscopy on reoxidizedsediments suggested that 15-50% of Tc bound tosediments was present as Tc(VII). Overall, these resultssuggest that Tc reoxidation behavior is not directly coupledto Fe or S oxidation and that the extent of Tc remobilizationis dependent on the nature of the oxidant.