Morphology, chemical and mineralogical composition of magnetic fraction of coal fly ash

The article presents in detail the geochemical and mineralogical characteristics of magnetic particles formed during energetic combustion of hard coal and lignite. The aim of the research was to assess their suitability as a source of possible raw materials necessary for the development of new technologies. Both hard coal and lignite fly ash, as well as the magnetic fractions separated from them, have been tested using various analytical methods. The chemical composition, phase composition, the size, and morphology of magnetically susceptible particles were determined. The main phases identified in the magnetic fraction are magnetite, hematite, and multicomponent phases, often trapped in aluminosilicate or calcium-aluminosilicate basic glass. In order to compare the chemical composition of the magnetic fractions and raw ashes, EF was calculated - the enrichment factor of the component in the magnetic fraction in relation to ash. Among the elements that have been enriched, apart from Fe, the following should be mentioned: Mg, Mn, Co, Nd, Cu, Ni, and Au. Only the concentrations of Cu and Ni in the magnetic fraction of lignite are much higher than the Clarke value (average concentration in ash), therefore the recovery of these raw materials can only be profitable from this ash. Research confirmed that when choosing the waste for the separation of metal concentrates, the content of the raw material in the ash is not always the most important, but also the form of its occurrence. [Display omitted] •Magnetic fraction of fly ash is a potential source of strategically important metals.•The form of elements' occurrence in fly ash determines if they can be recovered.•Ferrospheres usually coexist with aluminosilicate or calcium-aluminosilicate glass.•The ferrous phases with a dendritic, skeletal or polygons structure are trapped in the glass.•High enrichment factor for nickel and copper was noted.