Silica-enhanced lime sorbents for flue gas desulfurization have been prepared by pozzolanic hydration of Ca(OH) 2 with excess SiO 2 . As the hydration proceeded, new particles grew in clearcut features with regular micropores, consisting of chainlike aggregates. The increase in the specific surface area of the product particles with hydration was closely related to the conversion to calcium silicate. Even after the completion of the pozzolanic reaction, self-hydration of excess SiO 2 continued to make the particles with more clear-cut features but prevent the Brunauer-Emmett-Teller (BET) surface area from further increasing. The mole ratio of Ca/Si in the calcium silicate prepared was independent of its initial mole ratio and converged to 0.9-1.5, depending on the hydration temperature. Pressure hydration at temperatures above 100 °C dramatically accelerated the reaction, resulting in a less compact structure composed of smaller primary particles with the ultimate BET surface area unchanged.

Enhancement in the utilization of lime−silica solids for flue gas desulfurization has been experimentally investigated on the basis of their physical and chemical properties. Along the pozzolanic reaction, the utilization of Ca(OH)2 in the solids increased because of the increase in their BET specific surface area resulting from formation of a calcium silicate phase. Continued hydration of the excess SiO2 after the reaction had been completed, however, reduced the utilization of the sorbent particles because of undesirable precipitation of Si on the silicate. Increases in the initial SiO2/Ca(OH)2 ratio and the reaction temperature drastically reduced the period of preparation for solids having the same utilization and increased the maximum utilization. It is proposed that the changes in morphology and effective distribution of Si and Ca in the silicate phase were responsible for the latter utilization enhancement.

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