GEOCHEMISTRY AND MINERALOGY OF GREEK LIGNITES FROM THE IOANNINA BASIN

Mineralogical and elemental composition of 26 lignites/lignitic shales and their ashes from the Ioannina Basin were examined using X-ray dif fraction, X-ray fluorescence, and instrumental neutron activation anal ysis. Mineralogy consists of quartz, 2:1 interstratified layer silicat es, kaolinite, and gypsum. Illite, calcite, amphiboles, feldspars, and pyrite are the minor minerals in the samples. The major oxides SiO2, Al2O3, Fe2O3, TiO2, and K2O show an enrichment in the upper lignite-be aring interval within the succession, CaO shows the exact reverse tren d, and Na2O and MgO do not show any trends. Arsenic in the samples ran ges from 2 to 46 ppm, Br from 10 to 25 ppm, Cl from 61 to 278 ppm, and Se from 2 to 14 ppm. Vertically, As content decreases from the shallo wer interval II to the deeper interval I. Within interval II, Cr and B r show a decrease from top to bottom. The concentration of Br and Cl i s higher in the samples of low mineral matter, while the opposite is t rue for As. Laterally, there is an increase in Br and Cl from the nort hern 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 pro cesses related to high water table and subsurface water flow from the nearby phosphorite deposits are probably responsible for the high conc entration of U, Mo, Sb, and possibly, V. The enrichment of Se is due t o leaching from gypsum and/or anhydrite beds in the area. The rare ear th elements follow variations in the low-temperature ash, but more spe cifically, the light REEs tend to mimic variations in Th and Al2O3 con centration, 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 l ignitic shales, but these indices should be treated with caution. Vola tile organic sulfur, determined between ambient and 120 degrees C, is 0-44.3% of the total volatile sulfur, whereas sulfur lost between ambi ent and 950 degrees 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 desulfurization and atmospheric flui dized-bed combustion technologies are recommended to meet the stringen t sulfur emission controls.