Ca(OH)(2)/fly ash sorbents were prepared with different weight ratios. Their reactions with SO2 have been studied under the conditions similar to those in the bag filters of the spray-drying flue gas desulfurization system. The sorbent reactivity increased in general with decreasing Ca(OH)(2)/fly ash weight ratio. The reaction kinetics was well described by the surface coverage model which assumes that the sorbent was made up of plate grains and the rate was controlled by the chemical reaction on the grain surface and takes into account the surface coverage by products. For sorbents with Ca(OH)(2)/fly ash weight ratios than 10/90, the effect of weight ratio on the reaction was entirely represented by the effects of the intial specific surface area and the Ca content of the sorbent. (C) 2004 Elsevier Ltd. All rights reserved.