A thermodynamic model was developed to predict the distribution of phosphates between the liquid and the solid phases in a reactor used for extracting phosphoric acid from phosphate rock by the dihydrate process. Experimental data found in the literature for equilibrium constants were regressed and included in the model to obtain a more accurate representation of the thermodynamic equilibrium. In addition, the Edwards-Maurer-Newman-Prausnitz Pitzer-based model was used to represent the activity coefficients of all species, while published lime solubility data were used to find an expression for the self-interaction parameter of phosphoric acid. The model was validated by comparing its predictions to experimental citrate Soluble loss data taken from earlier work and yielded very good results. Simulation results for ionic strength, solution acidity, lime solubility, and citrate soluble loss were used to analyze the effects of temperature and solution sulfate and phosphate content on the dihydrate process. Decreasing temperature and increasing sulfate levels were found to raise the acidity and the ionic strength of the solution as well as minimize the citrate soluble loss.