Np(V) Retention at the Illite du Puy Surface

• Published in: Environmental science & technology 2023-08, Vol.57 (30), p.11185-11194
• Main Authors: Schacherl, Bianca, Joseph, Claudia, Beck, Aaron, Lavrova, Polina, Schnurr, Andreas, Dardenne, Kathy, Geyer, Frank, Cherkezova-Zheleva, Zara, Göttlicher, Jörg, Geckeis, Horst, Vitova, Tonya
• Format: Article
• Language: English
• Subjects: Absorption; Bentonite - chemistry; Energy resolution; Ferric Compounds; Ferrous Compounds - chemistry; Fine structure; Illite; Iron; Minerals - chemistry; Montmorillonite; Mossbauer spectroscopy; Occurrence, Fate, and Transport of Aquatic and Terrestrial Contaminants; pH effects; Retention; Smectites; Solvent extraction; Sorption; Spectrum analysis; Surface chemistry; Ultrastructure; X ray absorption; X-ray absorption spectroscopy
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.2c09356

In this study, Np­(V) retention on Illite du Puy (IdP) was investigated since it is essential for understanding the migration behavior of Np in argillaceous environments. The presence of structural Fe­(III) and Fe­(II) in IdP was confirmed by Fe K-edge X-ray absorption near-edge structure (XANES) and 57Fe Mössbauer spectroscopy. In batch sorption experiments, a higher Np sorption affinity to IdP was found than to Wyoming smectite or iron-free synthetic montmorillonite. An increase of the relative Np­(IV) ratio sorbed onto IdP with decreasing pH was observed by solvent extraction (up to (24 ± 2)% at pH 5, c 0(Np) = 10–6 mol/L). Furthermore, up to (33 ± 5)% Np­(IV) could be detected in IdP diffusion samples at pH 5. Respective Np M5-edge high-energy resolution (HR-) XANES spectra suggested the presence of Np­(IV/V) mixtures and weakened axial bond covalency of the NpO2 + species sorbed onto IdP. Np L3-edge extended X-ray absorption fine structure (EXAFS) analysis showed that significant fractions of Np were coordinated to FeO entities at pH 9. This highlights the potential role of Fe­(II/III) clay edge sites as a strong Np­(V) surface complex partner and points to the partial reduction of sorbed Np­(V) to Np­(IV) via structural Fe­(II).