Modelling of mutual diffusion for associated electrolytes solution: ZnSO₄ and MgSO₄ aqueous solutions

Abstract

We study mutual diffusion of associated electrolyte in water. A theory based on the Smoluchowski equation and on the mean spherical approximation is proposed. It is found to be valid up to molar concentrations. The values of the association constant obtained for ZnSO₄ and MgSO₄ aqueous solutions are consistent with further methods of measurements. Thanks to the elimination of fast variables method, the theory can be generalised to any association in solution. Comparison with molecular dynamics and Brownian dynamics simulations in the case of MgSO₄ indicates that the pair is a global association phenomenon since it corresponds to several association phenomena (contact ion pair and solvent separated ion pair).

Keywords:

• mutual diffusion
• electrolyte solutions
• mean spherical approximation
• ZnSO₄
• MgSO₄

Acknowledgements

We are grateful to P. Turq for several useful discussions.