Study on the crystallization mechanism and kinetics of calcium sulfate in desulphurization waste water
As the size and habit of calcium sulfate crystals in the desulfurization waste water can directly lead to their easy accumulation on heat exchange surfaces and difficulty to clear.The crystallization condition affects the production process,equipment configuration,and process economics.Therefore,the study of the crystallization mechanism of calcium sulfate and the corresponding crystallization kinetics of calcium sulfate can provide technical support for the reduction treatment and engineering design of this desulfurization waste water.The microscopic characteristics of the crystallization products were analyzed by means of microscope,SEM-EDS and XRD,and the crystallization mecha-nism and crystallization kinetics of calcium sulfate were studied.The results show that,the different pH value of the waste liquid can lead to the precipitation of different metal ions,and the heavy metal ions in the waste liquid precipi-tate first with the increase of alkalinity,then the magnesium ions in the waste liquid precipitate mainly in the form of magnesium hydroxide.The existence of chloride ion and other impurities in the waste liquor affects the crystallization and regularity of calcium sulfate crystal.The crystallization of calcium sulfate is a gradual process of crystal nuclea-tion,crystal growth,crystal cluster aggregation and grain growth,but the change rule is consistent with the crystal of pure calcium sulfate.The nucleation rate of calcium sulfate crystal in desulphurization waste liquor largely depends on the super-saturation of solution,the higher the super-saturation of calcium ion,the faster the crystallization rate.The growth process of calcium sulfate crystal during evaporation can be fitted into a 1.38 order reaction process,the reac-tion rate constant is 34.62,and the crystallization reaction rate equation is r=34.62C1.38.
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