A chemical model for the solubility of Friedel's salt (FS, 3CaO center dot Al2O3 center dot CaCl2 center dot 10H(2)O) was developed. The model was built with the help of the OLI platform via regression of experimental solubility data for FS in the Na-OH-CI-NO3-H2O systems. The solubility of FS in water was measured using a batch nickel autoclave over the temperature range of 20-200 degrees C, and the solubility product of FS (log(10) K-sp was obtained. It was found that the solubility of FS in water shows a maximum value as a function of temperature. The solubility of ES in 0-5 mol/L NaOH and 0-2.5 mol/L NaCl solutions was found to decrease with increasing NaOH and NaCl concentrations, because of the common ion effect; however, in 0-2.5 mol/L NaNO3 solutions, it was found to increase because of complexation. During the regression analysis, it was found that CaOH+ plays an important role in solubility modeling, and its dissociation constant was determined by an empirical equation. New Bromley-Zemaitis activity coefficient model parameters for the Ca2+-OH, CaOH+-0H(-), and CaCl+-OH- ion pairs were also regressed, using the experimental solubility data generated in the present study. The new model was shown to successfully predict the solubility of FS in mixed NaOH + NaNO3 solutions not used in model parametrization. With the aid of the newly developed model, the concentration and temperature effects on calcium species distribution were analyzed.