INVESTIGATION OF THE COMPOSITION OF DISPERSED PARTICLES IN FLY ASH AND DETERMINATION OF THE ROUTES OF PM10 FORMATION FROM THE MINERAL COMPONENTS OF LIGNITE

A systematic study of the compositions of individual particles smaller than 10 μm in size (PM10) in the dispersed fraction of fly ash from the pulverised combustion of lignite from the Kansk-Achinsk basin has been carried out by scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDS). It is established that microspheres and particles of nonspherical shapes, belonging by size to the class of environmentally hazardous suspended particles PM10, depending on the content of CaO, SiO2, Al2O3 and Fe2O3, form several groups in the formation of which different mineral precursors are involved. A significant part (64 %) of dispersed particles is characterised by high CaO content ranging from 40 to 68 wt%, about 1/3 of the particles contain increased amounts of aluminosilicate components (SiO2 and Al2O3) up to 82 and 40 wt%, respectively, and ~3 % of the particles exhibit high iron content (Fe2O3) within the range of 34-65 wt%. A comparative analysis of the relationship between the concentrations of macrocomponents in the form of dependences [SiO2] = ƒ[Al2O3] and [SiO2 + Al2O3] = ƒ[CaO + Fe2O3 + MgO] allows us to state that the main mineral precursors of environmentally hazardous suspended particles PM10 formed during lignite combustion are complex Ca,Mg,Fe-humates, feldspars, mostly anorthite, mica-like minerals of chlorite type, and quartz. During lignite combustion, feldspar and mica melt forming the glass phase. After humate oxidation, organically bound Ca, Mg and Fe form highly reactive oxides readily reacting with each other and SiO2, to be included in aluminosilicate glass with the formation of complex compounds of different composition: silicates, aluminosilicates, aluminoferrites.