Industrial & Engineering Chemistry Research, Vol.34, No.4, 1342-1351, 1995
Crystal-Growth and Agglomeration of Calcium Sulfite Hemihydrate Crystals
Crystal growth and agglomeration of calcium sulfite hemihydrate crystals from solution were studied by reacting Ca(OH)2 with NaHSO3 in a pH-stat semibatch crystallizer. Single platelet crystals and agglomerates of platelet crystals were produced in the pH range from 5.80 to 6.80. The crystallization mechanism changed from primary nucleation to crystal growth in the progressive precipitation. Using the titration curves, the growth rate was calculated from the titration rate at the final stage of operation. The crystal growth rates of calcium sulfite hemihydrate crystals were found to obey the parabolic rate law in the low supersaturation range. Another point to be noted is that the precipitates of calcium sulfite hemihydrate in agitated suspensions have a tendency to form agglomerates. It was found that the degree of agglomeration is a weak function of relative supersaturation and magma density, while the pH value is a key factor that affects the degree of agglomeration. Addition of EDTA also has an effect on the agglomeration of calcium sulfite hemihydrates.
Keywords:CONTINUOUS PRECIPITATION;KINETICS;CRYSTALLIZATION;MORPHOLOGY;MECHANISMS;CARBONATE;CONSTANT;HABIT