Fly
ashes belong to important byproducts, accompanying industrial
energy production based on combustion technologies. Dependent upon
the nature and characteristics of the used fuels as well as combustion
technologies and their conditions, fly ashes may exhibit different
physicochemical properties, limiting their potential applications
as raw materials. A burned hard coal, lignite, biomass, or heavy fuel
oil may generate fly ashes of various chemical, mineral, and phase
characteristics. Both process conditions and humidity can, in turn,
strongly influence final textural properties of such materials. Exhaust
gas cleaning technologies also cannot be neglected as important factors
potentially affecting textural and functional properties of the fly
ashes. For example, denitrification processes, where NH3 is used as a reducer, can result in the so-called ammonia slip,
when excessive, unreacted ammonia undergoes sorption on ash grains,
forming the corresponding ammonia salts. Such undesired effects can
be problematic for the consecutive use of fly ashes as raw materials
or components. The current work was focused on an in-depth analysis
of chemical, mineral, and phase compositions of fly ashes of various
origin. Their structural, textural, and functional characterizations
have been performed by means of X-ray fluorescence, X-ray diffraction,
scanning electron microscopy–energy-dispersive X-ray spectroscopy,
Brunauer–Emmett–Teller method, Raman and diffuse reflectance
infrared Fourier transform spectroscopies. The concentration of NH3(aq) in aqueous effluents was determined by ultraviolet–visible
spectrophotometry. On the basis of the obtained results, a hierarchical
algorithm for selecting the most important parameters for industrial-scale
pro-ecological applications was proposed. The ratio of Si/Al, the
main constitutive elements of fly ashes, both content and speciation
of iron and/or other transition metals, occurrence of alkali components
and carbonaceous residuals, content of ammonia, mineral and phase
compositions, grain diameters and morphology, and sorptive affinity
of water to surfaces of ashes were selected as crucial parameters,
remaining decisive for the successful exploitation of ashes as raw
materials.