The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)

Platon Gkamaletsos, Athanasios Godelitsas, Takeshi Kasama, Alexei Kuzmin, Markus Lagos, Theo J. Mertzimekis, Jörg Göttlicher, Ralph Steininger, Stelios Xanthos, Yiannis Pontikes, George N. Angelopoulos, Charalampos Zarkadas, Aleksandr Komelkov, Evangelos Tzamos, Anestis Filippidis

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    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 mu g g(-1)), along with minor U (15 mu g g(-1)), which are responsible for radioactivity (355 and 133 Bq kg(-1) for Th-232 and U-238, 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 Th4+ is due to its incorporation into an insoluble perovskite-type phase with major composition of Ca0.8Na0.2TiO3 and crystallites observed in nanoscale. The Th L-III-edge EXAFS spectra demonstrated that Th4+ ions, which are hosted in this novel nano-perovskite of BR, occupy Ca2+ sites, rather than Ti4+ sites. That is most likely the reason of no Th release in Mediterranean seawater.
    Original languageEnglish
    Article number21737
    JournalScientific Reports
    Volume6
    Number of pages13
    ISSN2045-2322
    DOIs
    Publication statusPublished - 2016

    Cite this

    Gkamaletsos, P., Godelitsas, A., Kasama, T., Kuzmin, A., Lagos, M., Mertzimekis, T. J., Göttlicher, J., Steininger, R., Xanthos, S., Pontikes, Y., Angelopoulos, G. N., Zarkadas, C., Komelkov, A., Tzamos, E., & Filippidis, A. (2016). The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud). Scientific Reports, 6, [21737]. https://doi.org/10.1038/srep21737