Kinetics and Mechanism of Lime Slaking

The slaking of lime followed by dissolution of the slaked lime was investigated using rotating discs prepared from calcium oxide and from calcium hydroxide. Good agreement was obtained between experimentally determined rates and activation energies and those calculated on the assumption that the rate of the overall process is governed by diffusion of calcium and hydroxide ions from the lime surface. For slaking in solutions of sodium hydroxide and of calcium nitrate, the process was slowed by the common ion effect in the manner predicted from our assumption. Slaking in solutions containing carbonate or aluminate was found to slow markedly as precipitated calcium carbonate or calcium aluminate coated the lime surface. Experiments using powdered lime supported the results of the rotating disc studies.