Ion Transport through a Modified Heterogeneous Bipolar Membrane and Electromembrane Recovery of Sulfuric Acid and Sodium Hydroxide from a Sodium Sulfate Solution

Abstract

The fluxes and effective transport numbers of sodium and sulfate ions through a aMB-2m modified bipolar membrane in a system with 0.5 M sulfuric acid solution and 1 M sodium hydroxide solution have been measured by a modified Hittorff method. It has been shown that the flux densities and effective transport numbers of sodium and sulfate ions are lower for a aMB-2m modified bipolar membrane in comparison with Russian MB-1 and MB-3 industrial bipolar membranes. The process of producing sulfuric acid and sodium hydroxide from sodium sulfate in an electrodialyzer with three-chamber unit cells, consisting of a Ralex CMH cation-exchange membrane, an aMB-2m modified bipolar membrane, and a Ralex AMH anion-exchange membrane has been studied. The use of an aMB-2m modified bipolar membrane makes it possible to produce solutions of sulfuric acid and sodium hydroxide with a concentration of about 1.4 mol-eq/L from sodium sulfate with a concentration of 0.5 M. Contamination of a sodium hydroxide solution with sulfate ions is an order of magnitude lower than nitrate ions in the process of obtaining nitric acid and sodium hydroxide from sodium nitrate. This is due to the greater exclusion of the sulfate anion from the cation-exchange layer of the bipolar membrane due to the greater value of its charge, as well as the larger size compared to the size of the nitrate anion.