Self-organized nanostructured anion exchange membranes for acid recovery

Abstract

Anion exchange membranes (AEMs) based diffusion dialysis (DD) is considered as a promising process for acid recovery from industrial acid wastewater due to its low energy consumption, easy installation protocol, and less operating cost. The driving force produced by the concentration difference between the feed side and dialysate side (usually is water) stimulates the separation of acids from salts in acid effluents (a spent liquor HCl/FeCl2 generated from steel refining industry). In this work, we prepared low cost, highly productive and self-organized nanostructured AEMs for acid recovery via DD. The AEMs were designed by introducing the quaternary ammoniums with long hydrophilic side chains into the hydrophobic poly(2,6-dimethyl-1,4-phenylene oxide) main chains, where the self-organized nanostructure was constructed through hydrophilic and hydrophobic micro-phase separation behavior. Afterwards, the thermo-crosslinking of -CH2Br segments put in order the nanostructures to cramp the active transport of the Fe2+ ions to improve the selectivity. The 1H NMR, XPS, in-situ FTIR and AFM techniques confirmed the reaction progress and micro-topography of the prepared AEMs, respectively. Consequently, from the DD results, the hydrophilic side chains were imperative to achieve high acid flux and the thermal crosslinking attuned the channels to promote the selectivity between the acid and salt. At 25 °C, the AEMs (except for QPPO-1.0 membrane) showed higher H+ dialysis coefficients (UH) ranged from 0.013 to 0.059 m h−1, and outstanding separation factors (S) from 19 to 197. The observed results were high as compared with a commercial membrane DF-120 (UH = 0.009 m h−1, S = 18.5) and some recently reported membranes for HCl/FeCl2 solution.