The detailed investigations of solubility of limestone und gypsum are essential for optimization of process conditions and operating material consumption in the flue gas scrubbers. This study compares thermodynamic predictions based on the Pitzer model for electrolyte activities with experimental data obtained from salt (gypsum, limestone, calcium adipat) solubility tests in aqueous model systems at high ionic strengths under different partial pressures of carbon dioxide. The high ionic strengths in these aqueous suspensions were achieved by addition of calcium chloride, calcium formate und calcium acetate. By means of measured data the Pitzer interaction parameters for ionic pairs Ca2+/HCO3-, Ca2+/SO42-, Ca2+/HCOO-, Ca2+/CH3COO- and Ca2+/(CH4)2(COO)22- at ionic strength up to 8 mol∙kg-1 were fitted and verified. The Pitzer parameters for interaction between calcium ions and carboxylic acid ions were published in this work for the first time. Also for the first time, the values of standard free energies of formation of calcium formate, calcium acetate and calcium adipate are published. The new model parameters allow a better calculation of thermodynamic equilibriums at industrial processes of flue gas cleaning.