Modeling thermodynamics and phase equilibria for aqueous solutions of trisodium phosphate

A computational model is developed to calculate thermodynamic phase equilibria in alkaline solutions of trisodium phosphate up to 100°C. A variety of data are used, including isopiestic measurements, freezing point data, vapor pressure data at 100°C, heat capacities, heats of dilution, and solubility measurements. Pitzer's ion-interaction treatment is used to model electrolyte solutions and many unknown parameters are determined from existing data through nonlinear least-squares fitting. Phase equilibria are determined by minimization of total Gibbs energy using a modification of the code SOLGASMIX. Results calculated using the model accurately predict experimental data.