A differential fixed-bed reactor was employed to study the reaction between iron blast furnace slag (BFS)/hydrated lime (HL) sorbent and SO2 under conditions similar to those in the bag filters of a spray-drying flue gas desulfurization system. The BFS/HL sorbent was prepared at a weight ratio of 30/70 with a slurrying time of 16 h and a slurrying temperature of 65 degrees C. The sorbent was highly reactive towards SO2 as compared with hydrated lime alone. Increasing the relative humidity of the gas significantly increased the initial reaction rate and the ultimate Ca utilization of the sorbent. The temperature and SO2 concentration had slight effects on the initial reaction rate and negligible effects on the ultimate Ca utilization. The reaction kinetics of the sorbent with SO2 was well described by the surface coverage model, which assumes that the sulfation rate is controlled by the chemical reaction on the sorbent grain surface and takes into account the surface covered by the product. The results of this study are useful for the design and operation of dry or semidry processes that use BFS/HL sorbents to remove SO2 from flue gas.