Kinetics of Nucleation and Growth of Calcium Carbonate and Calcium Sulphate Crystals from Aqueous Solutions
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tics of Nucleation and Growth of Calcium Carbonate and Calcium Sulphate Crystals from Aqueous Solutions A. Yu. Tikhonova, *, S. K. Myasnikova, and N. N. Kulova aKurnakov
Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia *e-mail: [email protected] Received October 2, 2019; revised November 11, 2019; accepted November 18, 2019
Abstract—The dependence of the induction period on supersaturation during the nucleation of CaCO3 and CaSO4 ∙ 2H2O is experimentally determined and the interfacial tension values are measured. Using the constant concentration method, the kinetics of crystal growth of both salts is studied, the dependences of the crystal growth rate on solution supersaturation are obtained, and the kinetic order of the growth reaction is determined. Possible mechanisms of nucleation and growth are considered. The kinetics of transformation of the solid phase during the entire process of reagent precipitation is studied. The evolutionary curves are compared with the calculation results for the previously proposed models. It is shown that the model dependences can be used to verify and adjust experimental data. Keywords: kinetics, models, nucleation, crystal growth, solution, sparingly soluble salts of calcium DOI: 10.1134/S0040579520030124
The previous study [1] was devoted to simulating the kinetics of reagent precipitation of poorly soluble calcium salts. This article presents the results of an experimental study of the kinetics of nucleation and growth of calcium carbonate and calcium sulfate dihydrate crystals and their comparison with the theoretical kinetic curves. Numerous publications on calcium carbonates and sulfates can be found in the scientific literature, since they are extremely widespread in nature and are used on a large scale in industry [2–5]. This includes quite a rather large number of publications on the kinetics of nucleation and growth of their crystals from aqueous solutions. However, there are few among them in which both the stages and the kinetics of eliminating supersaturation under the same conditions during the entire process would be studied. Reagent precipitation is characterized by great supersaturations and is more difficult to study compared to classical crystallization, since there are several competing stages with their own kinetics (mixing of reagent flows, chemical reaction, and nucleation) at the beginning of the process. They proceed simultaneously and quickly enough, so it is difficult to isolate the limiting stage. In addition, homogeneous (spontaneous) crystallization at high supersaturations is extremely sensitive to the processing conditions (up to the influence of microimpurities and uncontrolled random factors). Therefore, the nucleation process is difficult to control, and the obtained data are barely
suitable for calculating a crystallization process that is carried out in another apparatus and under other conditions. It should also be noted that the trajectory of the crystallization process can cross several zones with
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