•FeCO3 solubility data allow for deeper understanding and prediction of CO2 corrosion and CO2 mineralization.•Limited temperature dependency on FeCO3 solubility.•Extended UNIQUAC cable of describing FeCO3 solubility in water.•New calculated Gibbs energy and enthalpy of formation for FeCO3.•Activation energy for FeCO3 dissolution in water. FeCO3 is present as a CO2 corrosion product in many industrial processes and takes part in the natural CO2 mineralization process. This work presents the solid–liquid equilibrium of the system FeCO3-H2O at 5–120 °C. The FeCO3 solubility showed little temperature dependence. However, temperature affected kinetics as the rate constants for FeCO3 dissolution increased with temperature. The activation energy of FeCO3 dissolution in water was determined to 1.55 kJ mol−1. Gibbs energy of formation was found to be −653.27 kJ mol−1, and the enthalpy of formation for FeCO3 was −710.01 kJ mol−1 using the Extended UNIQUAC model. Extended UNIQUAC could predict the experimental solubility data of FeCO3 in water within an average absolute relative deviation of 0.08. The data obtained in this study creates the basis for reducing the consequences of CO2 corrosion and increasing knowledge of the CO2 mineralization process.