The precipitation mechanism of calcium carbonate in the gas‐liquid‐solid three phase at alkalescency condition

The precipitation of calcium carbonate in heat exchanger is a serious problem in seawater desalination which results in significant decrease of heat exchange efficiency and tedious cleaning. Decalcification pretreatment by acidic flue gas provides an efficient and economical solution to this problem, but few literature has been reported about the crystallization mechanism of CaCO3, including the supersaturation ratio, the relationship between the supersaturation ratio of the reaction solution and the crystallization growth rate of CaCO3 in the CO2‐CaCl2‐H2O system. In this study, the crystallization of CaCO3 was studied by combing the dynamic method and the static method to ensure the accuracy in measuring the carbonate ion concentration by chemical titration at pH = 8.0 in the CO2‐CaCl2‐H2O system. It was found that there existed an ion competition between HCO3− and CO2 (aq) in the CO2‐CaCl2‐H2O system, which led to fluctuations of CO2 absorption rate. The supersaturation ratio of the reaction solution still increased when the reaction crystallization rate was reduced. The variations of the concentration of HCO3−, CO32− and Ca2+ ions with time were investigated. The growth process of the vaterite was monitored and described on mesoscale. The crystallization of CaCO3 in the process of decalcification by acidic flue gas was studied by combing the dynamic and static method. It was found that there existed an ion competition between HCO3‐ and CO2 (aq) in the CO2‐CaCl2‐H2O system, which led to fluctuations of CO2 absorption rate. The supersaturation ratio of the reaction solution still increased when the reaction crystallization rate was reduced.