The physicochemical bases of calcium carbonate formation in modeling system CaCl2 + NaHCO3 + NH4OH

In the presence of water ammonia solution the calcium bicarbonate converts into insoluble calcium carbonate. Linearly independent chemical reactions of calcium carbonate formation with application of ammoniac solution were defined by the Gram matrix. As a result of the thermodynamic analysis the probability of calcium ions extraction from water solutions was established. To define thermodynamic constants the program "Calculation of chemical reactions equilibrium on a wide interval of temperatures by an enthalpy method" was applied. Based upon given equilibrium constants and the law of mass action a equilibrium concentration of calcium ions was calculated. Furthermore, experimental data on calcium carbonate removal from standard test solution were obtained. The maximum level of calcium ions extraction in a solid phase was 92.11%. The difference of equilibrium and operating concentrations defines a moving force of calcium carbonate formation that allows to calculate mass-transfer coefficient. The kinetics of CaCO
₃
formation in an ammoniac medium was studied. Analysis of kinetics of this process was carried out by means of Kazeeva-Yerofeev's equation with Sakovich's correction and the derived experimental data. The reaction order and activation energy of the chemical reaction were defined. These values show the process takes place in transition field.