On the basis of chemical equilibria, the model of sulfur dioxide solubility in solutions applied in FGD (flue gas desulfurization) systems with magnesium salts addition is developed. The influence of magnesium chloride or magnesium sulfate on solution ability to absorb SO2, pH, ions concentration, and calcium salts solubility is presented. The mechanisms leading to a decrease of calcium carbonate solubility and/or to limestone particle blinding caused by magnesium salts addition are proposed.