Prediction of electrolyte solubilities from minimal thermodynamic information

A method is proposed that permits the proper extrapolation of thermodynamic quantities represented by the Pitzer equations from 25 degreesC to other temperatures. The new method. which assumes temperature independent heat capacities, was tested for the NaCl-H2O system and found very satisfactory. A new evaluation of the NaCO3-H2O system according to the CALPHAD method is presented, and solubilities for the quaternary Na2CO3-NaCl-NaOH-H2O and its ternary subsystems are predicted. Limitations of (i) these predictions and of (ii) the Pitzer model regarding extrapolations to high molalities are discussed.