Reconnaissance study of mineral matter and trace elements in Greek lignites

Abstract

Mineral matter in low-temperature ashes, major oxides and trace elements were determined for twenty-eight selected lignite samples and their respective 1000°C ashes from various locations in Greece using X-ray diffraction, X-ray fluorescence spectroscopy and INAA. Lignites ashed at lower temperature (150°C) reveal the presence of quartz, feldspars, layer silicates, pyrite, gypsum, bassanite and anhydrite in all samples. In northwestern Greece (Epirus, Kozani, Florina and Ptolemais) calcite, siderite, magnesite, epsomite, hexahydrite, jarosite and meta-aluminite coexist with the common occurring minerals. Large variation in the concentration of major constituents in the 1000°C ashes is observed. SiO 2 varies from 11.98% to 87.72%, Al 2O 3 from 4.53% to 23.36%, Fe 2O 3 from 3.01% to 39.72%, CaO from 0.55% to 43.05%, MgO from 0.18% to 9.17% and SO 3 from 0.02% to 32.72%. Smaller variations are exhibited by TiO 2, Na 2O, K 2O and P 2O 5. These variations are attributed to the depositional environment. High concentrations of Pb (548 ppm), Zn (2991 ppm), Ba (1520 ppm), As (1131 and 1675 ppm), Mo (565 and 712 ppm), W (191–420 ppm) and Sb (69 ppm) are reported in the 1000°C ashes of the selected lignites from Serres and Drama, northern Greece. Samples from another location in northern Greece, Serres, yield >5000 ppm U while in Drama (Dipotama) U concentration reaches as high as 17,600 ppm. The U enrichment of lignites in these locations is attributed to the leaching of this element from the superimposed U-bearing volcanic rhyodacitic rocks of Oligocene age. In southern Greece, Peloponnesus, lignite samples from Megalopolis, Xidias, Drossato and Vounargo show high F ranging from 154 to 218 ppm. Present results indicate that not only the wide variety and combination of elements that can be used to fingerprint lignitic basins but also the possibility of extracting such valuable elements from lignites and their ashes whenever the concentration and economics warrants such an undertaking.