Research question 1. In which forms do the REEs and Sc reside in bauxite residue s mineral matrix? Sc Bayer process REE.

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1 Research question 1 In which forms do the REEs and Sc reside in bauxite residue s mineral matrix? Sc Bayer process Bauxite residue REE Sc scandium; REE rare earth elements

2 Methods 2 Based on material from Aluminium of Greece (Mytilineos) Mainly Electron Probe Microanalysis (EPMA) Laser Ablation ICP-MS Supported by Raman Microscopy Transmission Electron Microscopy (TEM)

3 Precursor REEs in bauxite (I) 3 Phase LREE Formula rhabdophane-(ce) (Ce)(PO 4 ) H 2 O + Parnassos-Ghiona Ghana Karst Lateri4c [1] [2] [3,4] [5] present present florencite-(ce) CeAl 3 (PO 4 ) 2 (OH) bastnäsite group Ce(CO 3 )F + parisite/synchysite/ röntgenite Ca 1 2 REE 1 3 (CO 3 ) 2 5 F hydroxylbastnäsite- (Nd) and -(La) + cerianite CeO 2? + HREE churchite YPO 4 2H 2 O + xeno4me YPO 4 + +

4 Precursor REEs in bauxite (II) 4 Currently identified: cerianite (CeO 2 ) The most frequently observed in present samples

5 REEs in bauxite residue (I): REE ferrotitanate phases 5 Primary mineral form (oxide/ carbonate) Reacted area (Na, Ca, Ti take part in reaction) Ca-titanate rim (minor amout of REE) REE concentration increases towards the core Ti, Ca, Na conc. increases towards the rim Solid solution series from (Ca, Na)(Ti,Fe)O 3 to (REE, Ca, Na)(Ti, Fe)O 3 i.e. perovskite to loparite e.g. (Ce 0.65 Ca 0.29 Na 0.12 (Nd,La,Pr) 0.05 Th 0.01 ) Σ=1.12 (Ti 0.47 Fe 0.45 Al 0.06 Si 0.05 ) Σ=1.03 O 3

6 REE minerals... perovskite? 6 Ideal perovskite structure ABX 3 Perovskite supergroup Single perovskites n Perovskite subgroup n Perovskite CaTiO 3 sensu stricto n Loparite (Na,REE)Ti 2 O 6 Extensive solid Solutions Structure is extremely flexible Diverse cations can occupy the A and B sites Broad studies on synthetic perovskites

7 REEs in bauxite residue (II): REE ferrotitanate phases 7 WDS quantitative mapping REEs up to 50 wt% Surrounded by Ca-Ti shell

8 REEs in bauxite residue (III): REE ferrotitanate phases 8 Solid solution character of LREE ferrotitanate series: (a) substitutions of Ca and Na with REE on A site and (b) complete transformation, where (REE + Na + Th) + (Fe + Al) = Ca + Ti.

9 REEs in bauxite residue (IV): Other REE phases (carbonate, phosphate) 9 Carbonate Y Phosphate LREE Phosphate

10 REEs in bauxite residue (IV): Other REE phases (Mn-adsorbed) 10 Manganeseassociated

11 Sc in bauxite residue (I): 11 hematite and goethite Main host is hematite Two populations: Sc depleted 40 ppm Sc-bearing 190 ppm Overall 170 ppm 55 % of total Sc AlO(OH) hosts some Sc in bauxite 15 % of total Sc in BX reased during digestion < 5 % in red mud

12 12 Intensity (a.u.) Sc in bauxite residue (II): hematite and goethite ppm Sc 25% of total Sc budget a) 240 Goethite μ-raman spectrum Experimental Goethite reference X Observations showing two distinctive iron oxides Wavenumber BR2018, (cm 7-10 ) May 2018 Athens; presentecd by Johannes Vind Intensity (a.u.) b) ppm Sc Hematite μ-raman spectrum Experimental Hematite reference R (Mgt?) Wavenumber (cm -1 )

13 Sc in bauxite residue (III): 13 zircon Zircon about 5000 mg/kg Sc on average About 10% of total Sc budget in residue

14 Sc in bauxite residue (IV) 14 Phase Bauxite Bauxite residue % of total Sc Hema4te 70 ± ± 20 Goethite? 25 ± 20 Diaspore/boehmite 15 ± 15 2 ± 2 Zircon 10 ± 5 10 ± 5 Titanium phases 2 ± 2 1 ± 1 Other / unaccounted 3 7

15 Summary 15 REE Sc Light n Perovskite-loparite solid solution series ((REE, Ca, Na)(Ti, Fe)O 3 ) n Carbonates, phosphates are minor n Oxyhydroxides, associated with Mn phases are minor Heavy n Phosphates (YPO 4 ) Hematite, goethite are the main hosts Minor hosts are zircon, AlOOH

16 For further reading: J. Vind, A. Malfliet, B. Blanpain, P.E. Tsakiridis, A.H. Tkaczyk, V. Vassiliadou, D. Panias, Rare Earth Element Phases in Bauxite Residue. Minerals 8, 77 (2018) 2. J. Vind, A. Malfliet, C. Bonomi, P. Paiste, I. Sajó, B. Blanpain, A.H. Tkaczyk, V. Vassiliadou, D. Panias, Modes of Occurrences of Scandium in Greek Bauxite and Bauxite Residue. Minerals Engineering 123, (2018) 3. Vind, A. Alexandri, V. Vassiliadou, D. Panias, Distribution of selected trace elements in the Bayer process. Metals 8 (5), 327 (2018)

17 17 THANK YOU FOR YOUR ATTENTION! Questions?

18 References 18 [1] Ochsenkühn-Petropulu, M.; Ochsenkühn, K.M. Rare earth minerals found in Greek bauxites by scanning electron microscopy and electron probe micro-analysis. Microsc. Anal. 1995, [2] Laskou, M.; Andreou, G. Rare earth elements distribution and REE-minerals from the Parnassos Ghiona bauxite deposits, Greece. In Mineral Exploration and Sustainable Development, 7th Biennial SGA Meeting; Athens, Greece, August 2003 ; pp Please state the Day Month Year of the conference. [3] Gamaletsos, P.; Godelitsas, A.; Mertzimekis, T.J.; Göttlicher, J.; Steininger, R.; Xanthos, S.; Berndt, J.; Klemme, S.; Kuzmin, A.; Bárdossy, G. Thorium partitioning in Greek industrial bauxite investigated by synchrotron radiation and laser-ablation techniques. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 2011, 269, , doi: /j.nimb [4] Gamaletsos, P.N. Mineralogy and Geochemistry of Bauxites from Parnassos-Ghiona Mines and the Impact on the Origin of the Deposits. PhD Thesis, National and Kapodistrian University of Athens: Athens, Greece [5] Mouchos, E.; Wall, F.; Williamson, B. High-Ce REE minerals in the Parnassus-Giona bauxite deposits, Greece. Appl. Earth Sci. 2017, 126, 82 83, doi: /