High-performance porous anion exchange membranes for efficient acid recovery from acidic wastewater by diffusion dialysis

Abstract In the sustainability concept framework, wastewater highly loaded with acid is considered as a valuable resource, rather than a waste. Diffusion dialysis employing anion exchange membranes is a feasible solution to extracting acid from this waste stream. However, conventional anion exchange membranes have dense spatial structures with no observable pores even at nanoscale, which limits the transfer of protons. Porous anion exchange membranes provide a practical avenue to enhance the proton transfer due to their unique spatial structure. In this study, novel porous anion exchange membranes were designed by one-step crosslinking and quaternization of porous brominated poly (phenylene oxide) membrane substrate by 1, 4-diazabicyclo [2.2.2] octane. The resultant porous anion exchange membranes showed a high performance in acid recovery by diffusion dialysis, due to their uniquely tailored microstructures including an extremely thin selective layer and high free space volume. Specifically, the optimal anion exchange membrane possessed an acid dialysis coefficient of 0.066 ± 0.003 m h−1 and an acid/salt separation factor of 96.9 ± 2.5 in the HCl/FeCl2 mixture solution, outperforming the commercial anion exchange membrane (i.e., DF-120, acid dialysis coefficient of 0.0085 m h−1 and acid/salt separation factor of 18.5). This study demonstrates the great potential in constructing advanced anion exchange membranes at large scale for efficient acid recovery from highly acidic wastewater to support environment sustainability.