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The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)
Gamaletsos, P.N.; 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). NPG Scientific Reports 6: 21737. https://dx.doi.org/10.1038/srep21737
In: Scientific Reports (Nature Publishing Group). Nature Publishing Group: London. ISSN 2045-2322; e-ISSN 2045-2322
Peer reviewed article  
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  • Gamaletsos, P.N.
  • 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.
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 232Th and 238U, 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 LIII-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.
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