Abstract
The kinetics of crystallization of calcium sulfate dihydrate has been studied in ammonia solutions at 65° as a function of supersaturation, ionic strength and added electrolytes. The rate of reaction follows an equation first-order in relative supersaturation with respect to the calcium concentration under conditions in which the concentration of sulfate ion is effectively constant during the reaction. The crystal growth proceeds towards equilibrium much more rapidly as compared with the process at low ionic strengths. Copper ion and anions such as phosphate, carbonate and molybdate, reduce the reaction rate and also appear to influence the kinetics of crystallization. Calcium sulfate hemihydrate, anhydrite and calcium carbonate crystals are effective nucleators for the growth of gypsum under the conditions of this work.
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