Modeling Closed Equilibrium Systems of H₂O-Dissolved CO₂-Solid CaCO₃

In many places in the world, including North Estonia, the bedrock is limestone, which consists mainly of CaCO₃. Equilibrium processes in water involving dissolved CO₂ and solid CaCO₃ play a vital role in many biological and technological systems. The solubility of CaCO₃ in water is relatively low. Depending on the concentration of dissolved CO₂, the solubility of CaCO₃ changes, which determines several important ground- and wastewater parameters, for example, Ca²⁺ concentration and pH. The distribution of ions and molecules in the closed system solid H₂O-dissolved CO₂-solid CaCO₃ is described in terms of a structural scheme. Mathematical models were developed for the calculation of pH and concentrations of ions and molecules (Ca²⁺, CO₃^2-, HCO₃^-, H₂CO₃, CO₂, H⁺, and OH^-) in the closed equilibrium system at different initial concentrations of CO₂ in the water phase using an iteration method. The developed models were then experimentally validated.