Elsevier

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Volume 68, Issue 6, June 1989, Pages 727-734
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Observations on the nature of fly ash particles

https://doi.org/10.1016/0016-2361(89)90211-1Get rights and content

Abstract

The surface and bulk properties of six coal-derived fly ash samples taken from air fall, air hopper collectors, magnetic precipitators, electrostatic precipitators, bottom ash, river sediment, and original coal were examined by various spectroscopic and microscopic techniques. All the fly ash samples were found to contain quartz, amorphous materials, mullite-sillimanite, magnetite, haematite, and a trace of a TiO2 mineral. The original coal samples contained a large amount of kaolinite, quartz, and amorphous material. The mechanical precipitator sample contained higher concentrations of Al, Si, Ti and a number of other trace elements, than samples from the air hopper and the river sediment. The air hopper sample contained large amounts of H, F, Na, Mg, K, and Fe, whereas the river sediment was more concentrated in C, P, and Ca. Microspherules of fly ash showed higher surface concentrations of C, Cl, and O, whereas Al, Fe, and Ti concentrations increased wih depth. Individual microspherules showed evidence of four remarkably different elemental assemblages rich in either Si, Ti, Fe or K. Irregular hollow grains composed mainly of Al and Si, indicative of mullite-sillimanite, were common in all fly ash samples examined. The mineralogy of the microspherules, irregular hollow grains, and clays showed the presence of pseudorutile, ilmenite, haematite, mullite-sillimanite, diaspore, carbonate (calcite), and kaolinite. Non-opaque microspherules contained an organic hydrocarbon compound on the water-rich surface and a Ti- or Fe-rich nucleus in the core, suggesting that hydrocarbons were carried along with the gaseous combustion products. The mineralogy indicated that these ashes were produced under conditions of low temperature and incomplete combustion.

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