The phase behavior (vapor-liquid equilibria and solid-liquid equilibria) and thermal properties of aqueous solutions of ions such as K+, Na+, NH4+, Ca2+, and Cl- in the presence of phosphoric acid (H3PO4, H2PO4-, and HPO42-) and nitric acid (HNO3 and NO3-) are described by means of the extended UNIQUAC model. Model parameters are evaluated on the basis of more than 2000 experimental data points. There is good agreement between calculated and experimental data points. The model parameters are valid in the temperature range from -18 to +122 degreesC and in the concentration range up to 12 m for the acids HNO3 and H3PO4.