AN EQUATION OF STATE FOR ELECTROLYTE-SOLUTIONS .3. AQUEOUS-SOLUTIONS CONTAINING MULTIPLE SALTS

An equation of state for mixtures containing electrolytes was derived by taking molecule-molecule interactions, charge-charge interactions, and charge-molecule interactions into account by using perturbation expansions based on their potentials. Previous calculations for a large number of aqueous solutions containing single strong or volatile weak electrolytes demonstrated the potential of this equation of state. In this paper, we give a new physical description of this model and extend the work to aqueous systems containing multiple salts. The only adjustable parameter in the model is related to the ionic size. In our previous papers, we had one parameter for each electrolyte (i.e., each ion pair). In this work, we have used a single adjustable parameter for each ion. These parameters were determined from mean ionic activity coefficient data for a large number of single-salt aqueous systems. The values then are used in the calculations for multisalt systems without any additional adjustable binary or ternary parameters. Preliminary calculations are presented for several double-salt aqueous solutions and one triple-salt system, CaSO4-MgCl2-NaCl-H2O. Our calculations are compared with experimental data and with calculations made with other models, which contain a number of adjustable parameters. This equation of state shows good agreement with experimental data over wide ranges of temperature and composition.