The paper discusses a calcium hydroxide (Ca(OH)2) sorbent, modified by the addition of calcium lignosulfonate, that was recently developed for use in EPA's LIMB (limestone injection multistage burners) 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 that unmodified sorbent. It also loses surface area more slowly, and retains more of its porosity, suggesting that it sinters more slowly than conventional sorbent. Therefore, in addition to reducing the particle size of Ca(OH)2 in some applications, calcium lignosulfonate also appears to cause the water of hydration to be bound less tightly, and to inhibit one or more of the diffusion mechanisms responsible for the process of sintering.