A square-well equation of state for aqueous strong electrolyte solutions

Abstract

A simple and accurate electrolyte-equation of state is introduced for correlation of the mean activity coefficients of strong aqueous electrolyte solutions. The nonelectrolyte contribution of the new electrolyte-equation of state is based on the cubic square-well equation of state, SWEOS, that is composed of the van der Waals repulsive part of EOS and the attractive term is based on the square-well potential. The explicit version of the mean spherical approximation (MSA) is adopted for electrostatic contribution of electrolyte solution. The new electrolyte-equation of state, eEOS, has three adjustable parameters per each salt that are optimized by correlation of the mean activity coefficients of more than 130 binary aqueous electrolyte solutions at 25 °C and 1 bar. Furthermore, the parameters are used for prediction of the osmotic coefficients and densities of several aqueous binary electrolyte solutions at 25 °C. Also the mean activity and osmotic coefficient of a number of electrolytes have been correlated in temperature range of 0–100 °C. Moreover, the ionic specific parameters are obtained for five binary aqueous electrolyte solutions by simultaneous fitting of mean activity, osmotic coefficient and apparent molal volume. The results demonstrate that the new eEOS can be applied for accurate representation of the activity and osmotic coefficients of the aqueous electrolyte solutions at wide range of the electrolyte concentration and temperature of binaries.