DETERMINATION OF KINETIC CHARACTERISTICS OF CALCIUM CARBONATE CRYSTALLIZATION PROCESS FROM LIQUID WASTE OF SODA PRODUCTION

Abstract

In this work, the kinetic characteristics of the crystallization process of calcium carbonate from liquid waste of soda production are considered. We have investigated that there is a possibility of implementing the process of precipitation of calcium carbonate under the conditions of an operating ammonia process for the production of soda ash, while using soda ash production waste. This will make it possible to simultaneously obtain a high-quality commercial product and solve some environmental problems of factories producing soda products. The kinetics of the crystallization process of calcium carbonate from solutions was studied by establishing the dependence of the degrees of precipitation of Са2+, НСО3 ¯ and СО3 2– ions on time under conditions of stoichiometric ratio of reactants at temperatures of 50, 70, 90°С. The results of the research showed that an increase in temperature leads to an increase in the degree of precipitation of the corresponding ions, which is explained by a decrease in the solubility of СаСО3. It was established that the decrease in the solubility of chemically precipitated calcium carbonate in sodium chloride solution with increasing temperature is explained by the fact that СаСО3 belongs to substances with inverse solubility. Although NaCl increases the solubility of calcium carbonate, according to the equation of the “salt” effect, it is determined that both in a pure solvent and in a solution of sodium chloride, the solubility of СаСО3 decreases with increasing temperature. Also, the kinetic characteristics of the calcium carbonate crystallization process (rate constant and reaction order) were investigated. By processing experimental data related to the degree of deposition of calcium ions, it was established that the rate of crystallization of СаСО3 is described by a second-order kinetic equation. This is evidenced by the invariance of the reaction rate constant over time at a certain temperature. A kinetic model of the calcium carbonate crystallization process was developed, which establishes the dependence of the degree of precipitation of СаСО3 on temperature, time, and absolute supersaturation of the initial solution. Based on the temperature dependence of the process rate constant according to the Arrhenius equation, the values of the pre-exponential factor k0 = 236.6060 mol-1·dm3·s-1, the activation energy E = 22.824 kJ/mol, and the rate constants at a temperature of 383°С, k = 0.1059 mol-1·dm3·s-1. The value of the activation energy indicates that the calcium carbonate crystallization process under these conditions takes place in the diffusion-kinetic (transitional) region. Thus, the speed of the crystallization process will be determined by the saturation of the initial solution, the degree of mixing of the reaction medium, the temperature, and the chemical composition of the liquid phase.