LASER μ-RAMAN INVESTIGATION OF GREEK BAUXITES FROM THE PARNASSOS-GHIONA ACTIVE MINING AREA

Δείγματα βωξίτη τα οποία αποκτήθηκαν από εταιρείες που εμφανίζουν ενεργή μεταλλευτική δραστηριότητα στην περιοχή Παρνασσού-Γκιώνας χαρακτηρίσθηκαν αρχικά με τη χρήση συμβατικών μεθόδων (οπτικό μικροσκόπιο, περίθλαση ακτινών Χ) και στη συνέχεια μελετήθηκαν χρησιμοποιώντας, για πρώτη φορά στη διεθνή βιβλιογραφία, προηγμένες μή-καταστροφικές φασματοσκοπικές τεχνικές σε μικροκλίμακα (Laser μ-Raman). Τα αποτελέσματα της παρούσας μελέτης έδειξαν πως ο τύπος του βωξίτη (διασπορικός ή μπαιμιτικός) μπορεί εύκολα να προσδιοριστεί, ανεξάρτητα από το είδος του δείγματος (πορώδες ^κό-τεφρό ή και συμπαγές ερυθρό-φαιό), μέσω της καταγραφής του φάσματος του στην περιοχή χαμηλών ενεργειών (250 cm' - 600 cm'1) όπου και είναι ευδιάκριτες συγκεκριμένες Raman ταινίες των πολύμορφων του ΑΙΟΟΗ (448 cm' για το διάσπορο και 362 cm'1 για τον μπαιμίτη). Η παραπάνω μικρο-μέθοδος θα μπορούσε να εφαρμοσθεί για τον άμεσο προσδιορισμό των ορυκτολογικών φάσεων τόσο στο εργαστήριο όσο και επιτόπου στα μεταλλεία, έτσι ώστε να αποφευχθούν έμμεσες και χρονοβόρες ολικές τεχνικές οι οποίες χρησιμοποιούνται έως και σήμερα (όπως π.χ. η περίθλαση ακτινών Χ).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

Neutralization of sludge and purification of wastewater from Sindos industrial area of Thessaloniki (Greece) using natural zeolite

Η ανάμειξη λάσπης από τη βιομηχανική ζώνη Σίνδου Θεσσαλονίκης με υψηλής ποιό- τητας φυσικό ζεόλιθο τύπου-HEU (τόφφος με 86 %κ.β. κλινοπτιλόλιθο-ευλανδίτη) σε ίσες ποσότητες, έδωσαν άοσμη και συνεκτική ζεολάσπη. Επίσης, η κατεργασία υγρών αποβλήτων pH 7,8 από την ίδια βιομηχανική ζώνη με υψηλής ποιότητας φυσικό ζεό- λιθο τύπου-HEU (88 %κ.β. κλινοπτιλόλιθο-ευλανδίτη), έδωσε διαυγές νερό pH 7,3, ελεύθερο από οσμές και βελτιωμένες τις ποιοτικές παραμέτρους κατά 60% για τα NO3 -, 76% για το χημικά απαιτούμενο οξυγόνο (COD), 100% για τα P2O5 και το Cr. Ταυτόχρονα, προέκυψε άοσμη και συνεκτική ζεολάσπη ως ίζημα. Η άοσμη και συνε- κτική ζεολάσπη που προέκυψε είτε από την ανάμειξη της λάσπης με τον φυσικό ζεόλι- θο, είτε ως ίζημα από την κατεργασία των βιομηχανικών υγρών αποβλήτων με φυσικό ζεόλιθο και κροκιδωτικά, είναι κατάλληλη για ασφαλή απόθεση, επειδή η καθήλωση των επιβλαβών συστατικών στους μίκρο/νάνο-πόρους του ζεόλιθου τύπου-HEU κα- θώς και στους μέσο- και μάκρο-πόρους του φυσικού ζεόλιθου, αποτρέπει την έκπλυσή τους από το νερό της βροχής, προστατεύοντας έτσι την ποιότητα των εδαφών, επιφανειακών και υπόγειων υδάτων.The commixture of sludge from Sindos industrial area of Thessaloniki with high quality HEU-type natural zeolite (tuff with 86 wt.% clinoptilolite-heulandite) in equal proportions, resulted in odourless and cohesive zeosludge. Also, the treatment of wastewater of pH 7.8 from the same area with high quality HEU-type natural zeolite (88 wt.% clinoptilolite-heulandite) resulted in production of clear water of pH 7.3, free of odours and improved quality parameters by 60% for the NO3 - content, 76% for the chemical oxygen demand (COD), 100% for P2O5 and Cr contents. Simultaneously, a precipitate of odourless and cohesive zeosludge was produced. The odourless and cohesive zeosludge produced either by the commixture of sludge with the natural zeolite or as precipitate from the treatment of industrial wastewater with the natural zeolite and coagulants, is suitable for safe deposition, since the fixation of the hazardous components in the micro/nano-pores of the HEU-type zeolite, as well as the meso- and macro-porous of natural zeolite, prevents their leaching by the rain water, protecting thus the quality of soils, surface and ground waters

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

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

New insights into hydrothermal vent processes in the unique shallow-submarine arc-volcano, Kolumbo (Santorini), Greece

We report on integrated geomorphological, mineralogical, geochemical and biological investigations of the hydrothermal vent field located on the floor of the density-stratified acidic (pH , 5) crater of the Kolumbo shallow-submarine arc-volcano, near Santorini. Kolumbo features rare geodynamic setting at convergent boundaries, where arc-volcanism and seafloor hydrothermal activity are occurring in thinned continental crust. Special focus is given to unique enrichments of polymetallic spires in Sb and Tl (6Hg, As, Au, Ag, Zn) indicating a new hybrid seafloor analogue of epithermal-to-volcanic-hosted-massive-sulphide deposits. Iron microbial-mat analyses reveal dominating ferrihydrite-type phases, and high-proportion of microbial sequences akin to "Nitrosopumilus maritimus", a mesophilic Thaumarchaeota strain capable of chemoautotrophic growth on hydrothermal ammonia and CO2. Our findings highlight that acidic shallow-submarine hydrothermal vents nourish marine ecosystems in which nitrifying Archaea are important and suggest ferrihydrite-type Fe31-(hydrated)-oxyhydroxides in associated low-temperature iron mats are formed by anaerobic Fe21-oxidation, dependent on microbially produced nitrate

Mordenite-bearing tuffs from Prassa quarry, Kimolos island, Greece

We studied the geological and technological features of altered pyroclastic rocks from the main Bentomine Kimolian Enterprises S.A. quarry, in the Prassa region on the northeastern part of the Kimolos island, Greece. Particular emphasis was given to a MOR-type (mordenite) zeolite-rich material, tuff, which also contains K-feldspars, opal-CT and clays (mainly smectite) according to X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS). Additionally, it was characterised by a relatively low SiO2 component (av. 70 wt%) compared to surrounding volcanic rocks. Mordenite crystals are alkali- (Na- and moreover K-) rich. According to trace-element discrimination diagrams (Zr/TiO2-b/Y), the protoliths of the mordenite-bearing tuffs could be trachyandesites, whereas Ti/Al-Eu/Eu* diagrams indicated a clear felsic affinity. Normalised REE patterns confirmed an expected negative Eu anomaly and a relative HREE depletion, whereas relevant multi-element diagrams indicated positive Cs, Rb, Th, Pb, U and Ta, negative Ba, P and Ti and compatible elements anomalies. The SSABET of the rocks reached a value of 63 m2/g. In that case, the CEC was measured to be 98 meq/100 g. The above data suggest that the industrial minerals exploited in the Prassa quarry show good capabilities for the development of new products for innovative industrial and daily uses. © 2010 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart

Paleogeography of the Eosahabi River in Libya: New insights into the mineralogy, geochemistry and paleontology of Member U1 of the Sahabi Formation, northeastern Libya

A large paleo-river of Miocene age traversing Libya from south to north has been previously demonstrated by seismic, stratigraphic, paleontological, and remote sensing data. The depositional environment of As Sahabi Formation in north central Libya is this large and now extinct Eosahabi River. However, the source of this major African river has remained controversial. Dark-colored sedimentary material with magnetic properties suggested a source from the basaltic Haruj as Aswad massif in south central Libya. To test this hypothesis, mineralogical and geochemical study of clayey sediments from three localities, P25, P28 and P96c, from fossiliferous Member U1 of the As Sahabi Formation, were carried out. Results strongly indicate very mature and re-processed sediments of continental origin, and felsic sources with no basaltic contribution. Thus the origin can be traced to an upland area of outcrop of rocks of Precambrian continental origin in northeastern Chad. An alternative scenario is that the Sahabi sediments originated from Precambrian outcrops in Ethiopia through an east-west river connection with the Nile. We consider this hypothesis unlikely, since it is based only on remote sensing data, and lacks any time control or geological supporting evidence. The abundant vertebrate fauna from the Sahabi Formation shows strong similarities with penecontemporaneous fossil faunas in Chad and is supportive of an origin of the Eosahabi River in Neogene mega-Lake Chad. © 2012 Elsevier Ltd

Isotopic analysis for degradation diagnosis of calcite matrix in mortar

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (δ13C and δ18O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/ recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO2 and water during calcite formation and degradation processes. Isotopic change of the initial δ13C and δ18O in carbonate matrix was caused by alteration of the primary source of CO2 and H2O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO2 from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter δ18O and δ13C in lime mortar. © 2009 Springer-Verlag

Geological sources of as in the environment of Greece: A review

This review summarizes the existing data about the geological sources of As in Greece; their variety and the relevant concentrations make Greece a peculiar territory to generalize and better understand the methodology for their assessment. These sources concern As-containing ores in active and abandoned mining areas, geothermal/hydrothermal waters, lignites in exploited and unexploited deposits, As-minerals in various rock types such as metamorphic rocks, and mineral dust originating in Sahara desert. It is considered that As release from the above sources, in conjunction with various anthropogenic As fluxes, occasionally creates distinct areas with contaminated groundwater, soils, marine and atmospheric environment. In general, Greece has been reported as a global As "hot spot" and it is argued that a significant amount of the Hellenic population might be affected by As pollution. The most important and permanent As source seems to be geothermal/hydrothermal fluids, due to faults and volcanic activity, affecting the underground, surface, and marine aquatic environment. © 2016 Springer-Verlag Berlin Heidelberg

Amorphous As-sulfide precipitates from the shallow-water hydrothermal vents off Milos Island (Greece)

Amorphous orpiment-like As-sulfides (As2S3) are the most common As phases precipitating in hydrothermal systems, yet there is a lack of information regarding their solid-state characterization. Using a combination of optical, SEM-EDS, micro-Raman and XANES/EXAFS applications, we investigated yellow-orange As- and S-rich sediments occurring in the shallow-water hydrothermal system off the coast of Milos Island, Greece. The precipitates have several morphologies, but are dominantly colloidal. Intriguing "biological" morphologies also exist (e.g., cell-like (~10μm), spirals (~20μm), and rounded "cinnamon bun" shapes (~20μm)). SEM-EDS data indicated that the precipitates have an As:S ratio similar to orpiment (average=0.58, range 0.51-0.63; n=8). Micro-Raman spectra indicated that orange colored precipitates appear to be dominated by poorly crystalline and/or amorphous arsenic sulfides with micro-amounts of more crystalline orpiment and impure sulfur. The yellow sediments also contained crystalline elemental sulfur in the form S8. Bulk As K-edge XANES spectra of the As-sulfide precipitates proved a valence of As corresponding to orpiment-type (As2S3) compounds (-1 to +3). EXAFS fitting results indicated that the studied material exhibits an amorphous orpiment-like structure with As ions coordinated by 3 sulfur atoms (CN=3.0). The As-S interatomic distance of the first shell is calculated at 2.279Å and the Debye-Waller factor (σ2) is 0.00427. These data suggest that the modeled structure of the studied precipitates is slightly S-deficient and ordered only in the first shell around As, resembling an orpiment-type structure, whereas higher shells are not present and must be disordered. The disorder phenomenon may be strictly produced either by the existence of occasional As-S-As bridges with As-As bonds or by the occurrence of As-O-As bridges, causing twisting of the AsS3 pyramids in the initial orpiment structure. This distortion in the higher coordination shells of the structural sheets creates the amorphous orpiment. © 2015 Elsevier B.V.