Estimation of Possible Supersaturation of Solutions During Ion Exchange in Porous Media

The phenomenon of isothermal supersaturation of solutions in a porous medium at ion exchange is studied on the basis of mathematical modeling. The phenomenon consists in the fact that the solution with concentration signi cantly higher than the maximal solubility of the substance is formed in the pores of sorbent and no precipitation occurs. The general nature of the phenomenon has been noted in the works of some authors and an explanation was given for the stability of the supersaturated solution in the micropores of ion exchangers. The question of why sediment does not appear in larger pores remains open. In this paper, a model of changing of the number of condensed phase particles in pores is proposed and estimates are obtained that allow one to determine the degree of possible supersaturation depending on the process parameters. It is shown that the phenomenon under consideration can be explained not by a change in thermodynamic conditions in a porous medium, compared to normal conditions, but by the e ect of dynamic equilibrium between the association of condensed phase particles in the inner part of the pores, their di usion and their decomposition near the surface of the ion exchanger grains. The proposed hypothesis is con rmed by quantitative studies and comparison with available experimental data.