Sorbents prepared with different Ca(OH)(2)/fly ash weight ratios were reacted with SO2 under conditions similar to those in the bag filters in the spray-drying flue gas desulfurization system. The reaction kinetics was well described by a generalized surface coverage model developed in this study. The model 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 variation in sorbent Ca molar content (M-1) and the surface coverage byproducts. The effect of Ca(OH)(2)/fly ash weight ratio on the reaction was represented by the effects of the initial specific surface area (S-g0) and M-1 of the sorbent on the kinetic parameters. Under the same reaction conditions, the sorbents with weight ratios greater than or equal to 30/70 had about the same initial reaction rate per unit surface area of the sorbent; their ultimate conversions increased linearly with increasing S-g0, being independent of M-1. The effects of relative humidity, SO2 concentration, and temperature on the reaction were unaffected by the Ca(OH)(2)/fly ash ratio. The results of this study are useful to the design and operation of the dry and semidry processes using Ca(OH)(2)/fly ash sorbents to remove SO2 from the flue gas.