Sorption and Redox Speciation of Plutonium at the Illite Surface

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• 作者：Nidhu lal Banik ; Rémi Marsac ; Johannes Lützenkirchen ; Alexandre Diascorn ; Kerstin Bender ; Christian Michael Marquardt ; Horst Geckeis
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：February 16, 2016
• 年：2016
• 卷：50
• 期：4
• 页码：2092-2098
• 全文大小：376K
• ISSN：1520-5851

文摘

The geochemical behavior of Pu strongly depends on its redox speciation. In this study, we investigated Pu sorption onto Na–illite, a relevant component of potential host rocks for high-level nuclear waste repositories, under anaerobic conditions. When contacting Pu (85% Pu(IV), 11% Pu(V), and 4% Pu(III); 8 × 10^–11 < [Pu]_tot/M < 10^–8) with illite in 0.1 M NaCl at pH between 3 and 10, Pu uptake was characterized by log R_d > 4 (R_d: distribution coefficient in L kg^–1). Small amounts of aqueous Pu(V) were detected in solution on contact with illite after 1 week, which is not expected to be stable at the measured redox potentials (Eh) in our experiments. This observation suggests time-dependent reduction of Pu(V) to Pu(IV). After one year, log R_d values had increased compared to those after 1 week due to the reduction of weakly adsorbing Pu(V). For pH < 5, Pu(IV) and Pu(III) coexisted in solution under our experimental conditions, showing that Pu(IV) reduction to Pu(III) occurred in the illite suspension. Taking (i) surface complexation constants determined for Eu(III)–illite interaction (with redox-insensitive Eu(III) as a chemical analogue to Pu(III)), (ii) the known constant for Pu(III)–Pu(IV) redox transition, and (iii) measured Eh and pH, overall Pu uptake was well-predicted.