Investigation of the Nonexchange Sorption of Diverse Electrolytes by a Heterogeneous Sulfonic Cation-Exchange Membrane

The nonexchange sorption of diverse electrolytes by an MK-40 sulfonic cation-exchange membrane has been studied by conductometry without separating solution and membrane phases. The data of sorption experiments performed within the framework of the two-phase microheterogeneous model of an ion-exchange material have been used to find the Donnan constant for the MK-40 membrane in solutions of electrolytes, namely, HCl, NaOH, NaCl, MgCl2, CaCl2, and BaCl2. The concentration of an electrolyte sorbed by the membrane has been determined as depending on the nature and concentration of an equilibrium solution. Factors that have the most significant effect on the concentration of a sorbed electrolyte and the Donnan constant, such as the specific moisture capacity of the membrane and the nature and charge of counter- and coions, have been studied. The volume fractions of the gel and equilibrium solution phases have been determined by two methods, i.e., from the experimental data on the membrane specific conductivity in solutions of different natures and concentrations and from the data on the nonexchange sorption calculated within the microheterogeneous model of the membrane structure. It has been shown that the Donnan constant may be calculated for the MK-40 membrane in the salt solutions by a simplified method from the data on the sorption of an electrolyte of only one concentration, provided that the volume fractions of the conducting phases in the membrane are known.