Sorption of Th(IV) onto Iron Corrosion Products: EXAFS Study

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• 作者：Ferran Seco ; Christoph Hennig ; Joan de Pablo ; Miquel Rovira ; Isabel Rojo ; Vicens Mart ; Javier Gimnez ; Lara Duro ; Mireia Griv ; Jordi Bruno
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：April 15, 2009
• 年：2009
• 卷：43
• 期：8
• 页码：2825-2830
• 全文大小：204K
• 年卷期：v.43,no.8(April 15, 2009)
• ISSN：1520-5851

文摘

Long-term performance assessment of nuclear waste repositories is affected by the ability of the outer barrier systems to retain radionuclides after possible corrosive leakage of waste containers. The mobility of the radionuclides released from the spent fuel depends strongly on the processes that take place in the backfill material. The interaction of steel corrosion products and radionuclides is part of such a scenario. In this work, the sorption of Th(IV) onto 2-line-ferrihydrite (FeOOH·H₂O) and magnetite (Fe₃O₄), used as models for steel corrosion products, has been studied using EXAFS spectroscopy. Sorption samples were prepared in 0.1 M NaClO₄ solutions at acidic pH (initial pH values in the range 3.0−4.2) either from undersaturation and supersaturation conditions with respect to amorphous ThO₂. Two oxygen subshells, one at 2.37 Å and another at 2.54 Å, were observed in the first hydration sphere of Th in the case of the ferrihydrite samples. Th−Fe distances for the different ferrihydrite samples are 3.60Å. These results indicate a corner sharing surface complex of Th(IV) ion onto the ferrihydrite surface where the Th atom shares one O atom with each of two coordinated octahedra. The longer Th−O distance accounts for coordinated water molecules. No significant changes in the structural environment of Th in terms of coordination numbers and distances were detected as a function of Th(IV) concentration. Magnetite samples sorbing Th(IV) also showed also a strong distortion of the O shell, but in contrast to ferrihydrite, two types of nearest Fe atoms were detected at 3.50 Å and 3.70 Å. These results indicate that Th(IV) ion sorbs onto the magnetite surface as bidentate-corner sharing arrangements to [FeO₆] octahedra and [FeO₄] tetrahedra.