Novel compact ion exchange membranes through suppressing reverse permeation for high-efficiency recovery of inorganic acids

Drived by high concentration difference between the dilute chamber and the concentrated chamber, the reverse permeation of acid ions and water seriously weakens the concentration effect of the targeted acids separated from acidic effluents through the electrodialysis process. Based on rational structure optimization of ion exchange membranes, we propose the TWEDMS membrane modules consisting of the compact ion exchange membranes, compared with the TWEDM membrane modules consisting of the loose ion exchange membranes for the recovery of HCl, HNO3, H2SO4 and H3PO4. Due to suppressing the reverse permeation of acid ions and water from the compact membrane structure, the TWEDMS membrane modules can provide higher concentration differences and current efficiencies for the recovery of HCl (2.177 mol L-1 and 39.07%), HNO3 (1.928 mol L-1 and 19.68%) and H2SO4 (1.532 mol L-1 and 40.60%) at 180, 160 and 220 min respectively, reflecting superior separation effects of inorganic acids from acidic effluents. Among the recovery of these inorganic acids by the TWEDMS membrane modules, the recovery of HCl shows the largest concentration difference (2.032 mol L-1) at 160 min in the electrodialysis process, while the recovery of H3PO4 provides the highest current efficiency (48.67%). According to the analysis of electrical energy consumption, the membrane resistance and water permeability coefficient can play an important role in the reduction of electrical energy consumption (for example, from 17.53% of TWEDMS to 15.08% of TWEDM for HCl at 180 min) for the recovery of inorganic acids from acidic effluents.