Reports of user experiments at ANKA...
Transcript of Reports of user experiments at ANKA...
Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft
Reports of user experiments at ANKA 2009/2010
KIT – The cooperation of Forschungszentrum Karlsruhe GmbH and Universität Karlsruhe (TH)
www.kit.eduKIT – University of the State Baden-Würrtemberg and National Laboratory of the Helmholtz Association
ANKA SYNCHROTRON RADIATION FACILITY
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Thorium chemistry in Greek bauxites and bauxite tailing (red mud) using Xray absorption spectroscopy
A. Godelitsas 1) , P. Gamaletsos 1) , T.J. Mertzimekis 2) , J. Göttlicher 3) and Ralph Steininger 3) 1) University of Athens, 15784, Zographou, Greece
2) Institute of Nuclear Physics, NCSR “Demokritos”, 15310, Aghia Paraskevi, Greece 3) Forschungszentrum Karlsruhe GmbH, Institute for Synchrotron Radiation, HermannvonHelmholtzPlatz 1, D
76344 EggensteinLeopoldshafen, Germany
Greece is the 11 th largest bauxite mine producer in the world (2.22×10 6 tons in 2008). The exploitation of karsttype deposits hosted into Mesozoic limestones in central Greece [1] is currently performed by three Greek mining companies (Aluminium of Greece S.A., S&B Industrial Minerals S.A. and ELMIN Hellenic Mining Enterprises S.A.) whereas there is also an Al industrial plant. The mineralogy of Greek industrial bauxites is not particularly variable. Diaspore and/or boehmite (AlOOH polymorphs), hematite (Fe2O3), magnetite (Fe3O4), goethite (FeOOH), kaolinite (Al2Si2O5(OH)4), anatase and/or rutile (TiO2 polymorphs) are the major phases. Typical Feenriched (redbrown) bauxite contains 57% Al2O3. Of special interest is the highquality Fedepleted or “bleached” (whitegrey) diasporic bauxite composed only of diaspore (in some cases FeCrdiaspore) and TiO2 polymorphs [2], containing 80% Al2O3. The chemical composition of all types of bauxite is rather complicated and, except major Al, Fe and Ti, almost all natural elements are present in various concentrations including natural actinides (U and particularly Th). The highest Th concentration, according to preliminary XRF and ICPMS analyses, corresponds to specific Fedepleted samples (up to 63 ppm in bulk). Gammaray spectra (HPGe detector) revealed for Fedepleted bauxite an average of 220 Bq/Kg corresponding to 228 Ac ( 232 Thseries), compared to 180 Bq/Kg for typical Feenriched bauxite. Evaluation of preliminary bulk geochemical data indicated that Th is correlated to LREE and U, particularly in Fedepleted bauxite. This is in line with previous implications about the potential relation of actinides with REE minerals [3] and new SEMEDS data which proved the presence of Th (and U) in LREE fluorocarbonate minerals. Moreover, Th is rather correlated to Fe in Feenriched bauxite, while there is no evident bulk correlation to Ti for all bauxite samples.
The aim of the present project was to investigate the solidstate chemistry of Th in Greek bauxites and bauxite tailing (red mud remaining after Bayer process and containing 108 ppm Th) by means of Synchrotron microXRF and –EXAFS in the ANKA SULX beamline. The white grey bauxite was studied in the form of proper rock slides embedded in epoxy resin (Fig. 1) whereas the red mud was also investigated in the form of powder. For the analysis about 50 mg of the powdered sample together with 100 mg of cellulose was pressed in pellets of 13 mm diameter. Thorium compounds (ThO2, Th(NO3)4) and pure mineral powders, containing Th in various ppm levels, such as zircon (ZrSiO4), fluoroapatite (Ca5(PO4)3F), bastnäsite (CeCO3F) and parisite (CaCe2(CO3)3F2) were used as reference materials.
Fig. 1: Fedepleted diasporic Greek industrial bauxite sample investigated in the SULX beamline of ANKA.
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The Synchrotron spectroscopic investigation of Fedepleted Greek industrial bauxite approved the presence of Th and revealed that the actinide element is particularly associated with Fe/Ti and Ti containing phases into distinct pisoliths (Fig. 2). The association of Th with Ti in bauxites is demonstrated for the first time in the literature. This can be explained on the basis of the same 4 oxidation state of Th and Ti, despite the relatively large difference in the ionic radius of 6 coordinated Th 4 and Ti 4 to Oatoms (0. 40 and 0.605 respectively). Relevant works have already indicated the presence of Th in ilmenite (FeTiO3) and rutile occurring in sand deposits [4 6]. Except Fe/Ti and Ticontaining phases (as well as LREE fluorocarbonate minerals), significant quantities of Th must also be contained in detrital zircons, detected by complementary SEMEDS, into the AlOOH matrix of bauxite.
e r
Ti Th
pot
pot
pot
Fig. 2: Synchrotron microXRF elemental maps of bauxite indicating the regions (Spot 2 & Spot 3) where EXAFS spectra were obtained
The recorded EXAFS spectra (under evaluation) may also give new insights into the mineralogy and geochemistry of Th in karsttype bauxites.
Acknowledgements The provision of the bauxite samples used for this study from the Greek mining companies Aluminium of Greece S.A., S&B Industrial Minerals S.A. and ELMIN Hellenic Mining Enterprises S.A. is gratefully acknowledged.
References
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G. Economou and T. Bakas, Geochim. Cosmochim. Acta 73 (200 ) A40 . [3] M. Ochsenk hnPetropoulou and K.M. Ochsenk hn, Eur. Microscop. Anal. (1 5) 13. [4] A. Filippidis, P. Misaelides, A. Clouvas, A. Godelitsas, N. Barbayiannis and I. Anousis, Env. Geochem.
Health 1 (1 7) 83. [5] R.F. Garrett, N. Blagojevic, Z. Cai, B. Lai, D.G. Legnini, . Rodrigues and A.P.J. Stampfl, Nucl. Instr.
Meth. A 467468 (2001) 8 7. [6] P. P. Haridasan, P. M. B. Pillai, R. M. Tripathi and . D. Puranik, Rad. Protect. Dos. 12 /4 (2008) 381.