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Chemical Characterization of Fly Ash Aqueous Systems¹

ABSTRACT

Aqueous chemistry of fly ash from a western coal-fired power plant was characterized through measurements of solubility of Ca, Mg, Na, K, OH, CO₃, HCO₃, Cl, SO₄, and B in filtrates from water and electrolyte suspensions of the fly ash obtained at various dilution ratios. Acid titrations of dilute suspensions of the fly ash were also characterized. The study also examined the quantitative relationship between electrical conductivity of the filtrates and their total ionic composition. Relative concentrations of Ca and OH ions in solution and the nature of the acid titration curves suggest that solutions of fly ash are nearly saturated in Ca(OH₂). Elements of low to moderate solubility, such as Ca, Mg, SO₄, and B, showed greater dissolution as the fly ash suspensions were diluted. Ammonium acetate (NH₄OAc-HOAc) solutions (pH 5) were found to extract essentially all Ca and S and > 50% of Mg in the fly ash. Substantial fractions of total B in the fly ash were extracted in water (27%) and in an initially acidified (pH = 3) 0.01N NaCl (41.4%). Positive and highly significant correlations were found between total ionic concentration and electrical conductivity of the solution. The slope of the straight-line relationship was, however, considerably less than that commonly used in describing soil salinity. It is concluded that aqueous systems of fly ash do not represent a true equilibrium and that there is a need to standardize methods of salinity and base analyses in fly ash.

Key Words: coal waste • ion solubility • B • electrical conductivity • salinity

¹ Contribution of the Dep. of Soil and Environ. Sci. and the Kearney Foundation of Soil Sci., Univ. of California, Riverside, CA 92521. Supported in part by a grant from Southern California Edison Co., 2244 Walnut Grove Avenue, Rosemead, CA 91770, under contract no. U0026901.

² Assistant Research Soil Chemist, Professor of Soil Science, and Research Assistant, respectively.

Received for publication October 15, 1979.

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