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Fate of Lu(III) Sorbed on 2-Line Ferrihydrite at Ph 5.7 and Aged for 12 Years at Room Temperature

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Fate of Lu(III) Sorbed on 2-Line Ferrihydrite at Ph 5.7 and Aged for 12 Years at Room Temperature The University of Manchester Research Fate of Lu(III) sorbed on 2-line ferrihydrite at pH 5.7 and aged for 12 years at room temperature. II DOI: 10.1007/s11356-018-1904-7 Document Version Accepted author manuscript Link to publication record in Manchester Research Explorer Citation for published version (APA): Yokosawa, T., Prestat, E., Polly, R., Bouby, M., Dardenne, K., Finck, N., Haigh, S. J., Denecke, M. A., & Geckeis, H. (2018). Fate of Lu(III) sorbed on 2-line ferrihydrite at pH 5.7 and aged for 12 years at room temperature. II: insights from STEM-EDXS and DFT calculations. Environmental Science and Pollution Research, 1-12. https://doi.org/10.1007/s11356-018-1904-7 Published in: Environmental Science and Pollution Research Citing this paper Please note that where the full-text provided on Manchester Research Explorer is the Author Accepted Manuscript or Proof version this may differ from the final Published version. If citing, it is advised that you check and use the publisher's definitive version. General rights Copyright and moral rights for the publications made accessible in the Research Explorer are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Takedown policy If you believe that this document breaches copyright please refer to the University of Manchester’s Takedown Procedures [http://man.ac.uk/04Y6Bo] or contact [email protected] providing relevant details, so we can investigate your claim. Download date:23. Sep. 2021 1 Fate of Lu(III) sorbed on 2-line ferrihydrite at pH 5.7 and aged for 12 years 2 at room temperature. 3 II: Insights from STEM-EDXS and DFT calculations 4 5 Tadahiro Yokosawaa,1,*, Eric Prestatb, Robert Pollya, Muriel Boubya,*, Kathy Dardennea, 6 Nicolas Fincka, Sarah J. Haighb, Melissa A. Deneckec, and Horst Geckeisa 7 8 aInstitute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Hermann-von- 9 Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany. 10 ([email protected], [email protected], [email protected], [email protected], 11 [email protected], [email protected]) 12 bSchool of Materials, University of Manchester, Manchester, M13 9PL, United Kingdom. 13 ([email protected], [email protected]) 14 cDalton Nuclear Institute, University of Manchester, Manchester M13 9PL, United Kingdom. 15 ([email protected]) 16 17 *Corresponding authors: [email protected] (T. Yokosawa), [email protected] 18 (M. Bouby) 19 1Present address: Institute of Micro- and Nanostructure Research, Friedrich-Alexander- 20 Universität Erlangen-Nürnberg, Cauerstraße 6, 91058 Erlangen, Germany. 21 22 23 Keywords 24 2-line ferrihydrite, Lutetium, Transformation products, Hematite, Goethite, Incorporation, 25 STEM-EDXS, DFT. 26 27 1 28 Abstract 29 Transformation products of 2-line ferrihydrite associated with Lu(III) were studied after 12 30 years of aging using aberration corrected high-angle annular dark field scanning transmission 31 electron microscopy (HAADF-STEM), high efficiency energy dispersive X-ray spectroscopy 32 (EDXS) and density functional theory (DFT). The transformation products consisted of 33 hematite nanoparticles with overgrown goethite needles. High efficiency STEM-EDXS 34 revealed that Lu is only associated with goethite needles, and atomic resolution HAADF-STEM 35 reveals structural incorporation of Lu within goethite, partially replacing structural Fe sites. 36 This finding corroborates those recently obtained by AsFlFFF and EXAFS spectroscopy on the 37 same sample (Finck et al. 2018). DFT calculations indicate that Lu incorporation within 38 goethite or hematite are almost equally likely, suggesting that experimental parameters such as 39 temperature and reaction time which affect reaction kinetics, play important roles in 40 determining the Lu uptake. It seems likely that these results may be transferable to predict the 41 behavior of chemically homologous trivalent actinides. 42 43 1. Introduction 44 Iron (hydr)oxides are widespread in nature and can play an important role in the 45 bioavailability and migration of environmental pollutants, such as heavy metal ions or 46 radionuclides (RNs) (Raiswell 2011; Baleeiroa et al. 2018). Iron (hydr)oxides will also form 47 upon steel canister corrosion in the near field of a high-level nuclear waste repository, thus 48 representing an additional barrier to the RNs’ migration to the far field. Ferrihydrite is a hydrous 49 ferric oxide that is poorly ordered and usually exists as a fine grained nanoparticulate with high 50 surface area (Cornell and Schwertmann 1996), allowing it to interact substantially with 51 pollutants present in aqueous environments (Michel et al. 2007; Xiu et al. 2018). However, it 52 is thermodynamically unstable and during aging will transform into more stable oxides, such 53 as hematite or goethite, with the nature of the transformation product depending on the 54 environmental conditions. The interaction of RNs with pre-formed ferrihydrite will immobilize 55 these species or retard their migration, either by surface adsorption and/or by structural 56 incorporation (Denecke 2006; Novikov et al. 2006; Geckeis et al. 2013; O'Loughlin et al. 2003; 57 Duff et al. 2002; Latta et al. 2012; Marshall et al. 2014; Finck et al. 2018; Xiu et al. 2018). 58 However, there is a risk that ferrihydrite immobilized RNs can potentially be released upon the 59 ferrihydrite’s transformation to hematite or goethite. Consequently, in order to be considered 60 as a stable RNs immobilization mechanism, information on the fate of RNs immobilized by 2 61 metastable ferrihydrite upon aging is of crucial importance (Tan et al. 2010). In general, 62 changes in the composition of mineral phases occur in the presence of water and are usually 63 slow processes in low temperature systems (Gorski and Fantle 2017). The use of samples aged 64 for long periods are thus essential for determining whether structural immobilization is stable 65 on the long-term or not. 66 Previous investigations using either the actinide Am(III) (Stumpf et al. 2006) or the 67 lanthanide Lu(III) (Dardenne et al. 2001) reported the formation of bidentate surface species 68 upon contact with pre-existing ferrihydrite in suspension, meaning that this lanthanide can be 69 used as non-radioactive chemical homologue for trivalent actinides. The fate of Lu(III) sorbed 70 onto pre-formed ferrihydrite upon aging in suspension at 70°C was investigated by microscopic 71 and spectroscopic techniques (Dardenne et al. 2002). X-ray diffraction and infrared 72 spectroscopy data have indicated a progressive transformation of ferrihydrite into a mixture of 73 hematite and goethite, while X-ray absorption spectroscopy (XAS) data showed that Lu(III) 74 progressively enters structural sites of hematite within a reaction time of only 238 hours 75 (Dardenne et al. 2002; Bouby et al. 2004). 76 As the size of the hematite and goethite particles can be just a few nanometers (Cornell and 77 Schwertmann 1996), they deserve particular attention as they can be highly mobile in the 78 environment. For such small particles, transmission electron microscopy (TEM) is the 79 technique of choice for their characterization with high spatial resolution. In general, TEM 80 combined with spectroscopic methods, such as energy dispersive X-ray spectroscopy (EDXS) 81 and/or electron energy loss spectroscopy (EELS), is applied in order to obtain elemental 82 information as well as particle size, morphological and crystal structure information for 83 individual nanoparticles (Utsunomiya and Ewing 2003; Brydson et al. 2014). However, it is 84 challenging to detect and locally analyze trace elemental levels (~0.1 atom %) for nanoparticles 85 (Brydson et al. 2014), especially for electron beam sensitive materials, such as goethite (Cornell 86 et al. 1983, Um et al. 2011). In order to acquire sufficient signal-to-noise ratios, high beam 87 currents are required and this increases the likelihood of beam-induced specimen damage. High 88 resolution TEM (HRTEM) is a powerful method to obtain structural information at the atomic 89 scale but cannot directly yield elemental information because the image contrast is dominated 90 by interference of electron wave scattered through the specimen. High-angle annular dark field 91 STEM (HAADF-STEM) is an alternative imaging approach where the contrast scales directly 92 with atomic number (Nellist and Pennycook 1999), making it especially useful for detecting 93 heavy elements in a lighter matrix material (Powell et al. 2011). 3 94 During the last decade, the X-ray detection efficiency of EDXS and the spatial resolution 95 in STEM have dramatically improved through the development of high efficiency EDXS 96 detector systems (Schlossmacher et al. 2010; Suenaga et al. 2012) and spherical aberration 97 correctors which allow high currents to be focused into a small electron probe (Batson et al. 98 2002; Varela et al. 2005). High efficiency EDXS detection helps to provide sufficient X-ray 99 signal while minimizing electron beam exposure of the specimen. Probe-side aberration 100 corrected HAADF-STEM imaging further improves the detection of individual heavy element 101 atoms in lighter matrices (Okuno et al. 2010) and this capability is exploited in this study to 102 provide detailed insight into the interaction of trace level heavy elements with nanoparticle 103 phases. To the best of the author’s knowledge, this is the first time that aberration-corrected 104 HAADF-STEM has been applied to study An/Ln incorporation into hematite/goethite systems. 105 Density functional theory (DFT) (Kohn and Sham 1964; Hohenberg 1964) using periodic 106 boundary conditions has evolved into a well-established theoretical tool for the investigation of 107 solid states. DFT provides theoretical structural information, which complements experimental 108 data, e.g. XAS, as well as additional information, like reaction energies, that are experimentally 109 more difficult to access (Skomurski et al.
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