Structural and kinetic parameters of the ion exchange membranes MС-40 and MA-41 in solutions of ammonium nitrate

Abstract

The electroconductivity of the heterogeneous cation and anion exchange membranes MС-40 and
MA-41 in the ammonium nitrate solution in wide concentration range has been studied. For the experiment,
contact-difference method of measuring the electrical resistance of the ion-exchange membranes was chosen.
This method allows us to work at very low concentrations of the external equilibrium solution. From the data
on the electroconductivity obtained by the maximum dilution, the diffusion coefficients of ammonium ions
and nitrate ions in the membranes were calculated: they are much less than in the solutions that is connected
with the high viscosity of the polymeric material as well as the movement of the counter ions in the field of
the charge of the fixed ions whose density is higher than in the solution. Using the micro heterogeneous twophase
model of the structure of the ion exchange material the shares of the conductivity of the gel and nongel
phases were determined. It is shown that for the anion exchange membrane the contribution of the phase of
the inner solution to the total conductivity of the sample is higher than for the cation exchange membrane.
This is due to a lower sorption capacity of the anion exchanger, and the low mobility of the nitrate ions in the
membrane in comparison with the ammonium ions in the cation exchanger. The points of
isoelectroconductivity of the membranes MС-40 and MA-41 in the solution of ammonium nitrate: the
equality of electroconductivities of the gel and nongel phases in the case of the anion exchange membrane is
observed at lower concentration of the external equilibrium solution. These results are necessary for calculate
ion of energy consumption in electrodialysis, mathematical modeling of electrodialysis desalination and
concentration processes, as well as forecasting the electrochemical behavior of ion exchange membranes in
the electro-membrane systems.