This research was aimed at recovering Fe and Al compounds to produce a useful complex coagulant from fly ash using H2SO4 and SO2 from flue gas oxidized to SO3 by NaClO3. The reaction kinetics of wet SO2 scrubbing from simulated flue gas with fly ash slurry was studied. The SO2 scrubbing experiments were carried out in a jacketed glass reactor system with a simulated flue gas containing SO2 and N2 in the gas phase and fly ash slurry in the liquid phase. Sodium chlorate was added to oxidize SO2 to SO3, adding H2SO4 in the slurry. The reaction orders of both Fe2O3 and Al2O3 extraction from fly ash slurry were shown to be 1.5. The empirical Arrhenius expressions were also derived from the reaction rate constants obtained at each reaction temperature. The mass transfer process of SO2 with ClO−3 was evaluated using a two-film theory model.