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Geochemistry and mineralogy of Greek lignites from the Ioannina basin

Foskolos Antonis, Goodarzi, Fari, Gentzis, Thomas, 1958-

Πλήρης Εγγραφή

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Περίληψη

Mineralogical and elemental composition of 26 lignites/lignitic shales and their ashes from the Ioannina Basin were examined using X-ray diffraction, X-ray fluorescence, and instrumental neutron activation analysis. Mineralogy consists of quartz, 2:1 interstratified layer silicates, kaolinite, and gypsum, Illite, calcite, amphi-boles, feldspars, and pyrite are the minor minerals in the samples. The major oxides SiO2, Al203, Fe2O3 TiO2, and K20 show an enrichment in the upper lignite-bearing interval within the succession, CaO shows the exact reverse trend, and Na2O and MgO do not show any trends. Arsenic in the samples ranges from 2 to 46 ppm, Br from 10 to 25 ppm, CI from 61 to 278 ppm, and Se from 2 to 14 ppm. Vertically, As content decreases from the shallower interval II to the deeper interval I. Within interval II, Cr and Br show a decrease from top to bottom. The concentration of Br and CI is higher in the samples of low mineral matter, while the opposite is true for As. Laterally, there is an increase in Br and CI from the northern to the central part of the basin, an increase of As in an eastern direction, and a decrease of Se in the same direction. Epigenetic processes related to high water table and subsurface water flow from the nearby phosphorite deposits are probably responsible for the high concentration of U, Mo, Sb, and possibly, V. The enrichment of Se is due to leaching from gypsum and/or anhydrite beds in the area. The rare earth elements follow variations in the low-temperature ash, but more specifically, the light REEs tend to mimic variations in Th and Al2O3 concentration, and the heavy REEs follow the TiO2 variation.The lignitic ash is “basic” in nature. Ash indices indicate low fouling tendency and low to high slagging potential for the lignites and interbedded lignitic shales, but these indices should be treated with caution. Volatile organic sulfur, determined between ambient and 120°C, is 0-44.3% of the total volatile sulfur, whereas sulfur lost between ambient and 930°C for all samples varies from 19.3% to 93.2%. This is of great importance because of the contribution of volatile sulfur to acid rain formation. Flue gas desulfurizotion and atmospheric fluidized-bed combustion technologies are recommended to meet the stringent sulfur emission control.

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