Two types of fly ash from fluidized bed (FBC) and pulverized coal combustors (PCC) were treated with calcium hydroxide (Ca(OH)(2)) to produce reactive SO2 sorbents. Treatment was performed using 28.6 mass% Ca(OH)(2)/fly ash mixtures slurried at 350 K for 8 h. Sulfation experiments were carried out in a thermogravimetric analyzer (TGA) at SO2 concentration ranging from 0.11 to 0.67 vol% and 1063-1153 K temperature range. At conditions close to those prevailing in an atmospheric FBC (1123 K, 3000 ppmv and 20 vol% excess air), about 92% and complete conversion of CaO to CaSO4 within 1 h reaction could be achieved with treated PCC and FBC fly ashes, respectively. Based on pore structural measurements for both sorbents, treatment enhanced the specific surface area (by about 8 times) as well as pore volume (by about 5 times). The shape of the N-2-adsorption/desorption isotherms, specific pore area, and pore volume distribution curves remained unchanged. Study of the intrinsic kinetics of the reaction between treated fly ash and SO2 indicated a first order reaction with respect to SO2 concentration up to 0.31 vol% SO2 (3.36 x 10(-8) mol/cm(3)). Activation energies of 82.3 and 89.0 kJ/mol were calculated for treated PCC and FBC fly ashes, respectively.