Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 3. Characterization of magnetic and char concentrates

The phase-mineral and chemical composition of magnetic (MCs) and char (CCs) concentrates recovered from five fly ashes (FAs) produced in four large Spanish thermo-electric power stations was characterized. The MCs and CCs were isolated by magnetic separation, sieving and froth flotation from FAs. The MCs recovered are in the range 0.7–4.1% and their phase-mineral composition (in decreasing order of significance) commonly includes Fe-rich aluminosilicate glass, magnetite, quartz, hematite, mullite, plagioclase, ferrian spinel, char, K-feldspar, wollastonite, anhydrite, and larnite. Other Fe, Mg, Ti, Mn, and Cr accessory minerals also occur in these fractions. The MCs are enriched in As, Ba, Co, Cr, Cu, Fe, Mg, Mn, Ni, U, and Zr in comparison with the FAs. The CCs recovered are in the range 1.6–22.8% and their phase-mineral composition (in decreasing order of significance) normally includes aluminosilicate glass, char (5–47% after sieving and 42–93% after flotation), quartz, mullite, and, to a lesser extent, magnetite, cristobalite, plagioclase, K-feldspar, wollastonite, hematite, anhydrite, calcite, kaolinite, larnite, and lime. The organic matter of CCs is mainly represented by anisotropic unfused, porous and coked components. The isotropic unfused inertinite and porous materials have subordinate occurrence in char. The CCs are enriched in Ag, Al, Cl, Cs, Cu, Rb, S, Sc, Se, Sr, Tb, V, and Zr in comparison with the FAs. Some genetic features, properties, possible environmental concern and potential utilization directions related to the MCs and CCs are also discussed.