LASER Μ-Raman INVESTIGATION OF GREEK BAUXITES FROM THE PARNASSOS-GHIONA ACTIVE MINING AREA

Abstract

Bauxite samples collected with permission from currently active mining areas in the Parnassos-Ghiona Mts district were studied using both conventional (optical microscopy and powder XRD) and, for the first time in the literature, micro-scale advanced non-destructive spectroscopic techniques, in particular Laser μ-Raman. The results showed that the different bauxite types (diasporic or boehmitic) can easily be identified regardless of sample type (porous white-grey or massive redbrown) by recording spectra in the low-wavenumber region (250 cm' - 600 cm' ) where distinct bands of the natural AlOOHpolymorphs are easily discernible (448 cm' for diaspore and 362 cm' for boehmite). The method described herein could equally be applied in the laboratory as well as in-situ at the mines for quick and accurate phase determination, in order to bypass the laborious and time-consuming indirect bulk techniques (such as XRD) routinely used to this date.

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

“…S2 ) is pointed out. Moreover, high levels of Th (111 μg g −1 ) have been determined using high-resolution (HR) γ-ray spectroscopy; rather higher than those reported in the literature 28 39 and references therein. The latter, and also minor U content (15 μg g −1 ), are responsible for the radioactivity of the studied BR (355 Bq kg −1 for 232 Th and 133 Bq kg −1 for 238 U) with a total dose rate of 295 nGy h −1 (see Supplementary Table S4 ).…”

“…The wavelength dispersive X-ray fluorescence (WDXRF) and, complementary, the inductively coupled plasma mass and optical emission spectroscopic measurements (ICP-MS/OES) of the studied BR proved that major Fe, Al, Ca, Si, Ti, Na and C, as well as significant volatiles (loss on ignition/LOI) comprise 86.5 wt.% and 13.6 wt.% of its chemical composition, respectively. In addition, when the trace elements’ concentrations of BR are normalized to the average values of Greek bauxites ( n = 16) 28 and of Upper Continental Crust (UCC) e.g. 28 and references therein , depletion in Ga (following the chemical behavior of Al) and enrichment -among others- in Cr (2403 μg g −1 ), V (1081 μg g −1 ), Ni (902 μg g −1 ), As (164 μg g −1 ), Pb (120 μg g −1 ), Sc (114 μg g −1 ) as well as in Cd, but also in Nb, Y, Ta, and REEs ( Supplementary Table S3 and Supplementary Fig.…”

“…In addition, when the trace elements’ concentrations of BR are normalized to the average values of Greek bauxites ( n = 16) 28 and of Upper Continental Crust (UCC) e.g. 28 and references therein , depletion in Ga (following the chemical behavior of Al) and enrichment -among others- in Cr (2403 μg g −1 ), V (1081 μg g −1 ), Ni (902 μg g −1 ), As (164 μg g −1 ), Pb (120 μg g −1 ), Sc (114 μg g −1 ) as well as in Cd, but also in Nb, Y, Ta, and REEs ( Supplementary Table S3 and Supplementary Fig. S2 ) is pointed out.…”

“…The fact that Th, which is primarily present in the minerals of the initial bauxite ore e.g. 27 28 , is subsequently transferred into BR through the Bayer process 11 12 , puts forward the claim that the deep knowledge about the localization of this actinide is mandatory, due to its environmental concern in the mining and metallurgical industry. However, the exact nature of this actinide element in the above natural (parent bauxite) and synthetic (bauxite metallurgical residue/BR) materials has been rather unknown, until the present paper.…”

Mineralogical and crystallographic characteristics of bauxites from some Grebnik’s (Metohija, Serbia) ore deposits

“…Furthermore, many bauxite ore deposits with mainly boehmite and/or diaspore composition dif fers from Grebnik's bauxite ore deposits either by: a). lack or minor of boehmite component (BÁRDOSSY, 1982;TEMUR & KANSUN, 2006;GAMALETSOS et al, 2007;ESMAEILY, 2010;LIU et al, 2010LIU et al, , 2012LIU et al, and 2017MOLLAI, 2011;AHMADNEJAD et al, 2017); b). lack or minor of diaspore component (BÁRDOSSY, 1982;MONGELLI et al, 2017); c).…”