Dissolution Kinetics of Aluminum, Calcium, and Iron from Circulating Fluidized Bed Combustion Fly Ash with Hydrochloric Acid

The dissolution of aluminum, calcium, and iron from calcined fly ash with hydrochloric acid was investigated using a batch reactor at temperatures from 315 to 345 K and over the acid concentration range of 1.4–6.0 M. Calcium was preferentially released compared to aluminum though these two elements in the calcined fly ash were mainly incorporated into the same mineralogical phase of anorthite. The dissolved fractions of aluminum, calcium, and iron increased with leaching time, but it decreased for silicon, which indicated the continuous precipitation of silicon during the leaching process. The dissolution kinetic data were successfully examined according to a semiempirical Avrami-type equation. The activation energies for dissolution of aluminum, calcium, and iron from the calcined fly ash with hydrochloric acid are 32, 28, and 19 kJ/mol, respectively.