Adsorption of Electrolyte Mixtures in Disordered Porous Media. A Monte Carlo Study†

Gregor Trefalt1 and Barbara Hribar-Lee1,*
1 Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia;

The adsorption of electrolyte mixtures with a common anion in a disordered porous media containing charges was studied using the grand canonical Monte Carlo method. The porous media (matrix) was prepared by a sudden quench of a model +1 : –1 electrolyte. A mixture of +1 : –1, +1 : –1 model electrolytes with ion sizes that correspond to HCl and NaCl water solutions was than allowed to penetrate such a material for a thermal equilibrium with an external bulk solution to be established. The systems were studied at different ionic strengths of the annealed electrolyte mixture and at different matrix concentrations. The results show similar trends as for electrolyte mixture adsorption in charged cylindrical micropores. At low matrix and annealed electrolyte mixture concentration the sorption of the ions is observed while at high concentrations the electrolytes get excluded from the matrix. As expected, the exclusion is stronger for the HCl solutions as a result of a weaker electrostatic attraction between H+ and matrix ions.

Keywords: Electrolyte mixtures, primitive model electrolyte, random porous media, separation factors, Donnan exclusion coefficients, ion-exchange isotherm, Monte Carlo simulation.