title: Sorption and Redox Speciation of Plutonium at the Illite Surface.
abstract: 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 Rd > 4 (Rd: 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 Rd 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.
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Nidhu Lal
authors.initials: NL
authors.lastname: Banik
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Rémi
authors.initials: R
authors.lastname: Marsac
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Lützenkirchen
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Diascorn
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Bender
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Christian Michael
authors.initials: CM
authors.lastname: Marquardt
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Geckeis
mesh_terms: D000327:Adsorption; D005063:Europium / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D010084:Oxidation-Reduction; D011005:Plutonium / Q000737:chemistry*; D011850:Radioactive Waste; D012965:Sodium Chloride / Q000737:chemistry; D064091:Waste Disposal Facilities
chemical_list: D008903:Minerals; D011850:Radioactive Waste; C099089:illite; D005063:Europium; D012965:Sodium Chloride; D011005:Plutonium