E. Tzamos

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.

Ammonium exchange capacity of the Xerovouni zeolitic tuffs, Avdella area, Evros Prefecture, Greece

Abstract Zeolitic tuffs from the Xerovouni location of the Avdella area (Evros Prefecture, Greece) contain on average 54 wt.% HEU-type zeolite, 6 wt.% smectite, 4 wt.% mica (64 wt.% microporous minerals), 8 wt.% alkali feldspar, 9 wt.% plagioclase, 11 wt.% cristobalite and 8 wt.% quartz (36 wt.% non-microporous minerals). The chemical formula of the HEU-type zeolite is Ca2.4K0.6Na0.4Mg0.3Al6.7Si29.3O72·17H2O and the tuffs contain on average 72.3 wt.% SiO2, 11.9 wt.% Al2O3, 1.2 wt.% Fe2O3, 1.0 wt.% MgO, 2.8 wt.% CaO, 1.3 wt.% Na2O and 1.9 wt.% K2O. The zeolitic tuffs show an average ammonium exchange capacity of 144 meq/100 g. HEU-type zeolite accounts for the most of the ammonium exchange capacity, while smectite and mica contribute to a relatively small extent. The ammonium exchange capacity of the Xerovouni zeolitic tuffs showed positive correlations with (a) the HEU-type zeolite content, (b) the total microporous minerals content, (c) the loss on ignition content and (d) the CaO content. Such materials could be used in a large variety of agricultural, aquacultural, industrial and environmental applications.

Quality assessment and hydrogeochemical status of potable water resources in a suburban area of northern Greece (Thermi Municipality, central Macedonia)

AbstractTwenty-seven (27) tap water samples were collected during October 2012 from the supply network of Thermi Municipality (central Macedonia, northern Greece) in order to assess their hydrogeochemical signatures and the overall quality status according to the European legislation and international standards. Samples were analysed for a total of 25 environmentally significant parameters including physicochemical properties (pH, EC, colour, turbidity and hardness), major and minor ions (Ca2+, Mg2+, , , , Cl−, , F−, and CN−) and trace elements (B, Sb, As, Cd, Cr, Cu, Pb, Hg, Ni, Se, and Mn). The vast majority of the parameters appeared in values below the maximum admissible concentration for potable waters. Individual elevated concentrations of B and may be attributed to natural (geogenic) factors related with local lithology and anthropogenic influences possibly deriving from agricultural practices (excessive use of N-fertilizers). The assessments of the analytical results were validated with the use of...

Natural radioactivity and trace element composition of natural clays used as cosmetic products in the Greek market

Abstract Seven commercial cosmetic clays having different colour (white, green, pink and red) available in pharmacies and herbalists’ shops in the Greek market have been examined for their trace element concentrations (Ag, As, Ba, Be, Cd, Ce, Co, Cr, Cs, Cu, Ga, Hf, Hg, La, Mo, Ni, Pb, Rb, Sb, Sc, Se, Sr, Tl, V, Y, Zn and Zr). According to EC Regulation 1223/2009 the presence of As, Be, Cd, Cr, Hg, Ni, P, Pb, Sb, Se, Te, Tl, Zr and their compounds is prohibited in cosmetics. The most abundant trace elements in the white clays were P (330 μg/g), Pb (220 μg/g) and Zr (11 μg/g) and for the green clays were P (1250 μg/g), As (43 μg/g), Cr (31 μg/g), Pb (30 μg/g) and Ni (23 μg/g). Red and pink clays had lower concentrations of these elements than their white and green counterparts. The green clays are three times enriched in As and the kaolinite-rich white clays are nine times enriched in Pb compared to the Average Shale. The main mineral phase in the white clays is either kaolinite or calcite, in green clays smectite, in pink clay kaolinite and talc and in red clays it is vermiculite. The specific activities of 238U, 226Ra, 228Ra, 228Th and 40K were determined by g-ray spectroscopy. The kaolinite-rich white clays are more enriched in 238U-series radionuclides (238U and 226Ra) than the smectitic green clays. In contrast, the green clays were more enriched in 232Th-series radionuclides (228Ra and 228Th) and 40K than the white clays.

Purification of wastewater from Sindos industrial area of Thessaloniki (N. Greece) using Hellenic Natural Zeolite

The treatment of wastewater from Sindos industrial area of Thessaloniki, Greece (initial pH 7.8) with the Hellenic Natural Zeolite (HENAZE), resulted to clear water of pH 7.3, free of odours and improved by 93% in the colour, 69% in the chemical oxygen demand (COD), >97% in the P2O5 removal, 54% in the NO3 removal and 77% in the Cr removal. The sorption and fixation of the different species from the wastewater by the micro- meso- and macroporous of HENAZE can be attributed to absorption (mainly ion exchange), adsorption and surface precipitation processes. Important role in these processes play the surface Broensted acidic and Lewis basic sites of the HEU-type zeolite. In addition the HENAZE treatment gave odourless and cohesive zeosludge, suitable for safe deposition since the fixation of dangerous components into the micro- meso- and macroporous of HENAZE, prevents the seepage of them by the rain water, protecting thus the quality of surface and underground waters. The used HENAZE sample, comes from Ntrista stream area of Petrota village (Evros Prefecture, Northeastern Greece) and contains 88 wt.% HEU-type zeolite, 4 wt.% mica + clays (92 wt.% microporous minerals), 5 wt.% feldspars and 3 wt.% SiO2-phases (quartz + cristobalite). The mineralogical composition and the physico-chemical properties, make the HENAZE suitable material for numerous environmental, industrial, agricultural and aquacultural applications.