title: The specific sorption of Np(V) on the corundum (α-Al2O3) surface in the presence of trivalent lanthanides Eu(III) and Gd(III): A batch sorption and XAS study.
abstract: The sorption of pentavalent neptunium, Np(V), on corundum (α-Al2O3) was investigated in the absence and presence of trivalent europium or gadolinium as a competing element under CO2-free conditions. The objective of this study was to investigate how a trivalent metal ion with a higher charge than that of the neptunyl(V) ion would affect the sorption of Np(V) when allowed to adsorb on the mineral surface before the addition of Np(V). Batch sorption experiments conducted as a function of pH (pH-edges) and as a function of Np(V) concentration (isotherms) in the absence and presence of 1×10(-5)M Eu(III) showed no sign of Eu being able to block Np sorption sites. Surface complexation modelling using the diffuse double layer model was applied to the batch data to obtain surface complexation constants for the formed Np(V) complexes on corundum. To account for potential changes occurring in the coordination environment of the neptunium ion in the presence of a trivalent lanthanide, X-ray absorption spectroscopy (XAS) measurements were carried out on the samples containing only Np(V) and Np(V)+Gd(III). The results reveal the presence of a bidentate Np(V) edge-sharing complex on the corundum surface in the absence of Gd(III), while the coordination environment of Np(V) on the corundum surface could be changed when Gd(III) is added to the sample before the sorption of Np(V).
authors: Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, 00014 University of Helsinki, Finland. Electronic address: sinikka.m.virtanen@helsinki.fi.
authors: S
authors: S
authors: Virtanen
authors: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstrasse 400, 01328 Dresden, Germany. Electronic address: f.bok@hzdr.de.
authors: F
authors: F
authors: Bok
authors: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstrasse 400, 01328 Dresden, Germany. Electronic address: a.ikeda@hzdr.de.
authors: A
authors: A
authors: Ikeda-Ohno
authors: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstrasse 400, 01328 Dresden, Germany. Electronic address: rossberg@esrf.fr.
authors: A
authors: A
authors: Rossberg
authors: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. Electronic address: johannes.luetzenkirchen@kit.edu.
authors: J
authors: J
authors: Lützenkirchen
authors: Institut für Nukleare Entsorgung, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany. Electronic address: thomas.rabung@kit.edu.
authors: T
authors: T
authors: Rabung
authors: Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, 00014 University of Helsinki, Finland. Electronic address: jukka.lehto@helsinki.fi.
authors: J
authors: J
authors: Lehto
authors: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstrasse 400, 01328 Dresden, Germany. Electronic address: n.huittinen@hzdr.de.
authors: N
authors: N
authors: Huittinen
keywords: Batch sorption; Eu(III); Gd(III); Np(V); Sorption competition; X-ray absorption spectroscopy