New local composition model for electrolyte solutions: single solvent, single electrolyte systems

A new model for representation of the excess Gibbs energy of electrolyte solutions is proposed. The model is based on the Electrolyte nrtl model according to Chen. However, considerable modifications have been introduced. The new model contains four adjustable parameters per binary electrolyte–solvent system. A new local composition expression is used, in which an energy correction term has been introduced empirically, based on calculation results from statistical thermodynamics. The paper gives computed values of the new model parameters for 163 aqueous electrolyte systems at 298.15 K. The parameters were obtained by correlating data on molal mean ionic activity coefficients and osmotic coefficients from the open literature. A comparison of the performance of the model is made with the Chen model, and shows that the new model may be used to very high concentrations with very good accuracy. An investigation of the temperature dependence of the model parameters has been made for some electrolyte systems over a wide range of temperatures and concentrations. The results show a slight temperature dependence of two of the parameters, while the two other parameters may be assumed independent of the temperature.