Abstract

Fly ashes produced by the combustion of coal, oil, and a coal-oil mixture have been studied by Auger electron spectroscopy and solvent leaching techniques. The Auger data indicate that the surface concentration of the metal ions Na, Fe, Mg, Ni, V, and Al as well as S and C increases on going from coal to coal-oil mixture and oil ash. The relative surface enrichments of oil and coal-oil-mixture and are consistent with a simple model of the ash-formation process, and the results confirm that several toxic metals are significantly enriched on the surface of the ash particles. The Auger data are compared to HCl and tris buffer leachate composition analyses, and in neither case does the leachate give an accurate representation of the surface composition. HCl apparently dissolves large oxide deposits and thus overestimates the surface concentrations of Fe, Al, and V. Conversely, several metallic ions are essentially insoluble in neutral aqueous solutions, so their surface concentration is underestimated by the tris leachate.

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