Leaching Behavior of Harmful Components from Cement Solidities of Fluidized-Bed Coal Ash

Solidifies of fluidized-bed fly ash with slag cement were prepared by hydrothermal treatment after adding gypsum, Na(3)PO(4), or Al(2)(SO(4))(3). XRD analysis of the solidifies was performed and leaching behavior of Pb and F from the solidities was investigated. The fly ash-cement and fly ash-cement-gypsum solidifies showed rather high leaching concentration of F and Pb. The F leaching was explained by solubility products of a Ca(OH)(2) - CaF(2) system. The Pb leaching concentrations roughly agreed with the theoretical curve for hydroxo complexes of Pb, showing a strong dependence on pH. Addition of Na(3)PO(4) and Al(2)(SO(4))(3), to cement solidities gave katoite and aluminium phosphate, and ettringite, respectively, and these solidities showed lower leaching concentrations of F and Pb than the fly ash-cement and fly ash-cement-gypsum solidifies. Capture of F and Pb in crystalline components such as ettringite probably accounts for such leaching suppression.