Nucleation and crystal growth of calcium sulfite hemihydrate

The rates of calcium sulfite dissolution, nucleation and crystal growth are important in slurry scrubbing processes for flue gas desulfurization. The rates affect the scrubber solution composition, SO;The dissolution and precipitation rates of platelet shaped calcium sulfite crystals were measured in a pH stat apparatus. The solution pH was varied from 3.0 to 6.0. The effects of sulfate content in the solids and solution were also investigated. The measured rates for the platelets were compared to the rates previously determined for agglomerates. It was determined that there are subtle differences between platelet and agglomerated calcium sulfite. The platelet sample with a low solid sulfate content dissolved and crystallized slower than the platelet sample with a high solid sulfate content. Low sulfate platelets also dissolved and crystallized slower than the agglomerated samples. The inhibiting effect of dissolved sulfate was also greater for the sample with low solid sulfate. The sample with high solid sulfate dissolved and crystallized at approximately the same rate as the agglomerates.;Size distributions can be predicted if nucleation and growth rates are known. These rates can also be used to examine prospects for increasing the calcium sulfite particle size. This would lead to an improved sludge quality and lower disposal costs. The nucleation and crystal growth rates of calcium sulfite hemihydrate were measured in a continuous flow crystallizer. The effects of solution sulfate concentration, residence time, suspension density and temperature on the rates were investigated. It was determined that the nucleation rate was directly proportional to the suspension density. The particle size distribution does not change when the suspension density is changed. The growth rate was found to be directly proportional to the solids residence time in the reactor. Therefore, calcium sulfite exhibits typical linear secondary nucleation behavior which can be predicted by a power-law expression. The activation energy for CaSO...