Equilibrium processes involving dissolved CO2 play a vital role in many biological and technological systems. Dissolved CO2 is an available carbon source for autotrophic organisms that have great natural and technological relevancy. In many places, including northern Estonia, the soil bedrock is limestone (CaCO3), which has a relatively small ion product and hence low solubility. However, in the equilibrium system CaCO3 ↔ CO32– ↔ HCO3– ↔ H2CO3 ↔ CO2 the solubility of CaCO3 is elevated, which causes a relatively high alkalinity (pH > 8) of surface and ground water as a result of increased concentration of CO32–, HCO3–, and OH– ions. In this paper the equilibrium processes involving CaCO3 (limestone) in liquid–gas–solid phase systems are described. The equilibrium distribution of ions and molecules in the system is described on the basis of a structural scheme. A mathematical model is presented for the calculation of pH and concentrations of ions and molecules in the equilibrium system CO32–, HCO3–, CO2, Ca2+, H+, and OH– at different concentrations of CO2 in its liquid phase using an iteration method. The developed model was experimentally validated.
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