Prediction of thermodynamic properties of aqueous electrolyte solutions

Graduation date: 1988The research undertaken in this study deals with three topics related to the prediction of thermodynamic properties of electrolytes in aqueous solutions. In the first, Pitzer ion interaction parameters for 304 single electrolytes were evaluated from recently published osmotic coefficient data at 25°C by using multiple regression analysis to fit model equations for osmotic coefficients. The Pitzer ion interaction model for electrolyte solutions, which has gained acceptance recently, was used in this study. The maximum molality fitted by this evaluation was the saturation concentration when data were available. The better agreement with experimental values were observed when using parameters which were obtained at higher concentration than those used by Pitzer. In the second, Pitzer ternary mixing parameters for 49 ternary mixture electrolytes with common ion at 25°C have been obtained by fitting all experimental data of lnr± or ∅ to the model equations. The effects of the higher order electrostatic term were considered for all asymmetrical systems. A comparison between the values of lnr± or ∅-1 calculated from the results of this study and experimental values for several systems shows the good agreement within ±1 %. The third study deals with the development of correlations between the ion interaction parameters and ionic properties (entropy, charge, and radius) to provide a method of estimating ion interaction parameters. A close relationship between two of the binary interaction parameters, β(0) and β(1), was observed. The correlation obtained between β(0) and β(1) could be used to predict the activity coefficients of various types of electrolytes where no experimental data are available. The resulting correlations were evaluated by comparing their estimates of activity coefficients with measured values. For 1-1 type of electrolytes, the correlations predicted the activity coefficients within 10% of the mean absolute values of the relative deviation for activity coefficients up to maximum molality 6.0 M. For higher valence electrolytes, however, the mean values of the relative deviation for activity coefficients are higher than for 1-1 electrolytes. The main reason is that the plot of β(0) versus β(1) is more scattered than with 1-1 electrolytes. For ternary mixture, the results from using correlation fit the experimental values within ±1% for system of HC1-MgC1₂-H₂0 at 25°C