Temperature and density effects on the high temperature ionic speciation in dilute Na+/Cl− aqueous solutions

Molecular simulation of dilute NaCl aqueous solutions is performed to study the Na+/Cl− ion-pair association and the constant of equilibrium between the solvent separated (shared) and contact ion pairs at high temperature. Using the simple point charge, the Pettitt–Rossky, and the Fumi–Tosi models for the water–water, the ion–water, and the ion–ion interactions, we determine the density dependence of the constants along the Tr=T/Tc=1.05 isotherm, and the temperature dependence along the ρr=ρ/ρc=1.5 isochore. The simulation results for the association constant are then compared with the predictions of two recent correlations based on conductance measurements at high temperature. The outcome of the comparison is interpreted in terms of the microstructural behavior of the solvent around the ions and the realism of its dielectric behavior.