The crystalline form, size and chemical composition of calcium sulfite prepared by heterogeneous reaction of the systems of Ca (OH)
2-SO
2 and CaCO
2-SO
2 in a continuous operation were compared with those of the semibatchwise reaction products. The effect of reaction temperature on the form of particles produced by continuous reaction was remarkable in the same manner as the semibatchwise reaction. Crystals of calcium sulfite hemihydrate were obtained as a spherical mass, flowery mass, formless mass and a form of plates depending on the temperature ranging from 5 to 90°C. It was revealed that the continuous reaction products, except flowery mass, had the particle diameters of 2-3 times that of the semibatchwise reaction products. The quantity of SO
2 of calcium sulfite hemihydrate produced from hydroxide or carbonate by semibatchwise reaction depended on the reaction temperature, that is, SO
2 decreased with decreasing reaction temperature. In the case of continuous reaction of Ca (OH)
2-SO
2 system, the quantity of SO
2 did not depend on the reaction temperature, and was always about 48.0 wt%. Effects of Ca (OH)
2 and SO
2 concentration, pH, circumferential velocity of stirring impeller and residence time of the suspension in reactor on the shape and diameter of crystal or mass of crystals were investigated, too. Further, it was revealed that calcium sulfite tetrahydrate was synthesized by the continuous reaction (5°C), as well as the semibatchwise reaction, with the presence of sodium citrate (1.0 × 10
-2 mol/l).
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