title: The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud).
abstract: We present new data about the chemical and structural characteristics of bauxite residue (BR) from Greek Al industry, using a combination of microscopic, analytical, and spectroscopic techniques. SEM-EDS indicated a homogeneous dominant "Al-Fe-Ca-Ti-Si-Na-Cr matrix", appearing at the microscale. The bulk chemical analyses showed considerable levels of Th (111 μg g(-1)), along with minor U (15 μg g(-1)), which are responsible for radioactivity (355 and 133 Bq kg(-1) for (232)Th and (238)U, respectively) with a total dose rate of 295 nGy h(-1). Leaching experiments, in conjunction with SF-ICP-MS, using Mediterranean seawater from Greece, indicated significant release of V, depending on S/L ratio, and negligible release of Th at least after 12 months leaching. STEM-EDS/EELS &HR-STEM-HAADF study of the leached BR at the nanoscale revealed that the significant immobility of Th(4+) is due to its incorporation into an insoluble perovskite-type phase with major composition of Ca(0.8)Na(0.2)TiO3 and crystallites observed in nanoscale. The Th L(III)-edge EXAFS spectra demonstrated that Th(4+) ions, which are hosted in this novel nano-perovskite of BR, occupy Ca(2+) sites, rather than Ti(4+) sites. That is most likely the reason of no Th release in Mediterranean seawater.
authors.affiliation: Center for Electron Nanoscopy, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.|Faculty of Geology &Geoenvironment, National and Kapodistrian University of Athens, Zografou Campus, 15784 Athens, Greece.|Karlsruhe Institute of Technology, ANKA Synchrotron Radiation Facility, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Platon N
authors.initials: PN
authors.lastname: Gamaletsos
authors.affiliation: Faculty of Geology &Geoenvironment, National and Kapodistrian University of Athens, Zografou Campus, 15784 Athens, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Godelitsas
authors.affiliation: Center for Electron Nanoscopy, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kasama
authors.affiliation: Institute of Solid State Physics, University of Latvia, Kengaraga str. 8, 1063 Riga, Latvia.
authors.forename: Alexei
authors.initials: A
authors.lastname: Kuzmin
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Lagos
authors.affiliation: Faculty of Physics, National and Kapodistrian University of Athens, Zografou Campus, 15784 Athens, Greece.
authors.forename: Theo J
authors.initials: TJ
authors.lastname: Mertzimekis
authors.affiliation: Karlsruhe Institute of Technology, ANKA Synchrotron Radiation Facility, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Göttlicher
authors.affiliation: Karlsruhe Institute of Technology, ANKA Synchrotron Radiation Facility, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Ralph
authors.initials: R
authors.lastname: Steininger
authors.affiliation: Department of Electrical and Computer Engineering, Nuclear Technology Laboratory, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.|Department of Automation Engineering, Alexander Technological Educational Institute of Thessaloniki, 57400 Thessaloniki, Greece.
authors.forename: Stelios
authors.initials: S
authors.lastname: Xanthos
authors.affiliation: KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, 3001 Leuven, Belgium.
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Pontikes
authors.affiliation: University of Patras, Department of Chemical Engineering, 26500 Rio, Greece.
authors.forename: George N
authors.initials: GN
authors.lastname: Angelopoulos
authors.affiliation: PANalytical B.V., 7600 AA Almelo, The Netherlands.
authors.forename: Charalampos
authors.initials: C
authors.lastname: Zarkadas
authors.affiliation: PANalytical B.V., 7600 AA Almelo, The Netherlands.
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Komelkov
authors.affiliation: School of Geology, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece.
authors.forename: Evangelos
authors.initials: E
authors.lastname: Tzamos
authors.affiliation: School of Geology, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece.
authors.forename: Anestis
authors.initials: A
authors.lastname: Filippidis