A calcium hydroxide [Ca(OH)2] sorbent modified by the addition of calcium lignosulfonate has recently been developed for use in the Environmental Protection Agency's limestone injection multistage burner process. The increased reactivity with sulfur dioxide (SO2) displayed by this modified sorbent has been shown to be caused, in part, by its decreased particle (agglomerate) size compared to conventional Ca(OH)2. Subsequent work has shown that surfactant-modified Ca(OH)2 also undergoes significantly different structural changes during furnace injection. For a given reactor temperature and residence time, the modified sorbent calcines to a greater extent than unmodified sorbent. It also loses surface area more slowly, and retains more of its porosity, suggesting that it sinters more slowly than conventional sorbent. Therfore, in addition to reducing the particle size of Ca(OH)2 in some applications, calcium lignosulfonate also to inhibit one or more of the diffusion mechanisms responsible for the process of sintering.