The application of bipolar membranes MB-2 modified by chromium (III) hydroxide for sodium sulfate conversion process

The conversion process of sodium sulfate by electrodialysis with the application of bipolar membranes MB-2 modified with chromium (III) hydroxide has been realized. The investigation of the modified membranes operated under H+ and OH- - ions generation mode in an electrodialysis unit for 50 h of discontinuous operation has revealed the concentration increase of chromium and oxygen at the surface of the test samples, which can be ascribed to chromium (III) hydroxide surface segregation. However, it does not result in major changes of electrochemical properties of the modified membrane. This is confirmed by reproducibility of current-voltage characteristics, by stability of acid current efficiency during exploitation, as well as by minor changes in electrochemical impedance spectrum.The maximum sulfur acid and sodium hydroxide concentrations obtained in the recycling mode of the process of 0.5 mol/dm3 sodium sulfate conversion with the modified membranes application are 0.48 and 1.10 mol/dm3 when the salt solution and acid solutions are put into the unit with varied rate.