Сonjugate transport of ions and heat through the cation exchange membrane during electrodialysis of slight soluble electrolytes

Abstract

       Thermodynamics of irreversible stationary processes is applied to the analysis of interaction of ion and heat fluxes during electrodialysis with alternating cation-exchange and anion-exchange membranes. In the basis of the description process is the Onsager law, which considers the ion fluxes as a linear function of the generalized forces. From the theorem on the production of entropy as a bilinear function of flows and generalized thermodynamic forces, the gradient of the electric potential is taken as a generalized thermodynamic force for the ion flow, and the temperature gradient for heat flows. To calculate the total flow rate when applying electric potential and temperature gradients, the thermophysical characteristics of ionexchange membranes, including thermal conductivity coefficients, as well as the electric mobility of ions by
contact-difference method were previously determined.
       The experiments were carried out with a five-section electrodialyzer with alternating heterogeneous cation-exchange membranes MK-40 and anion-exchange MA-40. The object of the experiment was the suspension of a slightly soluble electrolyte of strontium sulfate, which provided a constant concentration in the diluate section, and the process simulated dissolution of precipitation during reverse electrodialysis and extraction
of strontium from radioactive effluents. The constancy of the concentrations in the section filled with strontium sulfate was achieved by the transfer of strontium cations through the cation exchange membrane, and anions through the anion sulfate through the anion exchange membrane. The deficiency of ions in the saturated suspension solution was compensated by the dissolution of the precipitate. Good agreement was obtained between the experimental and calculated results corresponding to the Onsager linear law. The General result of intensification of heat shows more than twofold increase in flows in the range of 20-50, which is comparable to hydrodynamic the intensification of migration of ions when using turbulized flows spacers.