Possible Degree of Isothermal Supersaturation of Solutions During Ion Exchange
DOI:
https://doi.org/10.17308/sorpchrom.2026.26/13690Keywords:
mathematical modeling, isothermal supersaturation, ion exchange, dynamic equilibriumAbstract
The phenomenon of isothermal supersaturation in a porous medium during ion exchange was studied. This phenomenon consists in the formation of the solution with a concentration significantly higher than the maximum solubility of the substance under normal conditions, and no precipitation occurs inside the pores of the sorbent. This process is common in nature, for example, during geochemical processes of ore formation. The effect has been observed experimentally since the 1979-80s. This phenomenon allows the processing of concentrated solutions.
In the studies of a number of authors, the general nature of the phenomenon was noted and an explanation for the stability of a supersaturated solution in the micropores of ion exchangers was provided. The question of why sedimentation does not occur in larger pores remains open. There are no known quantitative relationships that determine the possible degree of supersaturation, depending on the concentration of the dissolved substance and the physical parameters of the porous medium.
This study demonstrates that the phenomenon of isothermal supersaturation of the solution in the pores of the ion exchanger can be explained not by a change in thermodynamic conditions, compared to normal ones, but by the effect of a decrease in the amount of supersaturated phase in the form from which a precipitate can be formed. This decrease is the result of a dynamic equilibrium between the aggregation of condensed phase particles in the interior of the pores and their disintegration near the surface of the sorbent grains.
Using the modeling of the process it is possible to calculate the possible maximum degree of supersaturation of the solution in a porous medium at which precipitation does not occur. The modeling should take into account: the relationships that determine the aggregation and disintegration of supersaturated phase particles in the solution; the heterogeneity of the electrostatic potential near the surface of the sorbent grains; the diffusion and transport of the solution; the influence of such parameters as flow rate and sorbent grain size on the process.
The obtained modeling result should be compared with the literature data on the experimental observation of the supersaturation process.
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