MINERALOGICAL AND CHEMICAL INVESTIGATION OF FLY-ASH FROM THE MAIN AND NORTHERN LIGNITE FIELDS IN PTOLEMAIS, GREECE

Lignite fly ash from the Main and Northern lignite fields of Ptolemais, Greece, is mainly composed of anhydrite, lime, calcite, gehlenite and quartz. Also present, in minor and trace amounts, are portlandite, hatrurite, akermanite, ettringite, plagioclase, alkali feldspar, mica, gypsum, bassanite, brownmillerite, tobermorite and unburnt lignite. Calcite, quartz, feldspars and mica were initially contained in the mined lignite. Anhydrite, lime, portlandite, gehlenite, Akermanite, hatrurite and brownmillerite were formed due to the ashing process at different temperatures (> approximately 400-degrees-C), while gypsum, bassanite, ettringite and tobermorite were formed due to the subsequent soaking of the fly ash, at temperatures around 42-200-degrees-C. The chemical composition of the fly ash corresponds approximately to that of coal combustion slags, lignite fly ash of Gardanne-Provence, France, and Portland clinker. The chemical and mineralogical composition of the fly ash reveal properties of concern to the construction industry and even to health and the environment.