HEATING EXPERIMENTS OF THE PTOLEMAIS LIGNITE IN THE TEMPERATURE-RANGE FROM 100-DEGREES-C TO 500-DEGREES-C

Lignite samples from the southern lignite field of Ptolemais basin have been heated in air at 100-degrees-C intervals, in the temperature range from 100-degrees-C to 500-degrees-C. After air quenching and cooling the ash samples (+/- unburnt lignite) were examined by X-ray diffraction analysis for their mineralogical composition. The minerals detected in the different ash samples are: calcite, dolomite, quartz, illite, kaolinite, meta-kaolinite, pyrite, hematite, bassanite, anhydrite, wollastonite, tilleyite and spinel. Calcite, dolomite, quartz, illite, kaolinite, pyrite and hematite are considered as constituents of the starting lignite. Calcite, dolomite, quartz and hematite are present in all ashing temperatures. Bassanite is present in 100-degrees-C and 200-degrees-C ash samples and is formed by the dehydration of gypsum. Anhydrite appears in 300-degrees to 500-degrees-C ash samples and is formed by the de-hydration of bassanite. Anhydrite and hematite can be formed by the pyrite-calcite reaction. Pyrite is absent in the 500-degrees-C ash sample. Above 400-degrees-C kaolinite dehydrates to meta-kaolinite, while illite is not longer detectable.