A thermodynamic model was developed based upon five equilibrium reactions to predict the limits of distribution of phosphates between the liquid and the solid phases in a reactor used to extract phosphoric acid from phosphate rock. A computer code was generated to carry out different simulations of the model using several inputs of temperatures and liquid phase sulfuric acid contents. Ideal Solution, Debye- Hückel, and Robinson-Guggenheim-Bates electrolyte activity coefficient models were employed alternately in each simulation to complete the thermodynamic model and the outputs were compared to one another. Experimental data of equilibrium constants were regressed to adjust their parameters to obtain a more accurate representation of the thermodynamic equilibrium. Results for ionic strength, liquid phase pH, and phosphate lattice loss were used to analyze temperature and liquid phase sulfuric acid content effects on the reacting system.