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A recovery of calcium resource from such solid waste as coal burnt ash, which involves a large amount of calcium-derived compounds, was investigated by extraction with organic acids. The effect of organic acid on the quality of extracted solid product was studied, in terms of the amount of recovered calcium component and impurities, by employing 6 organic acids: formic acid, acetic acid, propionic acid, oxalic acid, malonic acid and succinic acid. Extraction was performed by dissolving the coal ash samples with organic acid and by filtrating the solid residue to separate the calcium-rich solution. Calcium in the coal ash sample was dissolved with the organic acid, and CaO was recovered from the resulting solution by the evaporation followed by the calcination at 900 °C.As the results, it was found that CaO content in the extract was concentrated up to 75.7-92.7 % from coal burnt ash containing 33.9 % of CaO. The enrichment of CaO was related with pKa value of organic acid. Increasing in pKa value resulted in higher yield of CaO with lower amount of such impurities as SiO2, Al2O3 and Fe2O3.A highly porous structure of CaO extracted with organic acid was obtained. The pore diameter and the pore volume of extracted CaO were 0.31-1.35 μm and 2.02-2.74 l / kg, respectively, compared to those of calcined limestone: 0.075 μm and 1.18 l / kg. Owing to highly porous structure of extracted CaO with organic acid, the capacity of extracted CaO for dry sorption of SO2 was found to be about 2 times larger than that of CaO obtained by calcination of limestone.

Separation and Enrichment of Calcium Component by Extraction of Coal Burnt Ash with Organic Acid.