Leaching characteristics of boron and selenium for various coal fly ashes

The leaching characteristics of B and Se for coal fly ash (CFA) were examined. Twenty-one CFA samples were subjected to a leaching test, in which CFA was shaken with pure water in a liquid to solid ratio (L/S) of 100 for 24 h at room temperature. The correlation between the leaching amount and the concentration of element in CFA was investigated. The leaching amounts of B, Ca, S, and Se were essentially dependent upon their concentrations in CFA. As the degree of % leaching was higher, the leaching amount was more dependent upon the concentration. Also, the leaching test was performed under constant pH conditions. The leaching of Se tended to increase as the pH in the aqueous phase was raised. For CFA samples, which gave large degree of Ca leaching amount, the leaching of B and Se was decreased especially under high alkaline conditions. The effects of pH and the presence of leached Ca ion in the aqueous phase upon the leaching behavior were discussed.