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.
The status of boron (B) in coal, fly ash and other associated residues and its impacts on soils and plants are reviewed and discussed. Laboratory and greenhouse experiments with fly ash derived from a western U.S. coal source were conducted to examine solubility of B in the ash and its mobilization in soils and plants. Increasing dilution of the fly ash aqueous system or the soil-fly ash mix increased B solubility. Three hours of extraction were sufficient to remove all water soluble B, while extended extraction resulted in readsorption of soluble B. Acid and calcareous soils treated with up to 8% fly ash by weight and cropped under greenhouse conditions contained up to an average of 9 μg B/ml in the extract. Accumulation of B in alfalfa, bermudagrass and white clover grown on the treated soils was found dependent upon rate of application and type of soil, with white clover showing the highest accumulation. Tissue B was positively and linearly correlated with B determined in water saturation extracts from the treated soils.
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