Quaternary ammonium functionalized poly(arylene ether) (QPAE-Br) membranes based on 2,2 0 ,6,6 0 -tetramethyl biphenol for diffusion dialysis (DD) were designed and successfully fabricated via nucleophilic substitution polycondensation, bromination, film casting, and quaternization. The structures, thicknesses, ion-exchange capacities (IECs), water uptakes, swelling ratios, ion conductivities, and mechanical properties of QPAE-Br were used to characterize the membranes. The influence of the membrane structures on the DD performances was investigated by DD tests of simulated industrial pickling wastewater (1 mol/L HCl, 0.1 mol/L FeCl 2 ). The DD results show QPAE-a (IEC 5 1.51 mmol/g) as the best DD candidate. Predialysis treatments further improved the DD performances of QPAE-Br. QPAE-a exhibited an excellent proton diffusion coefficient (U H 1 ) of 0.033 m/h and a high separation factor (S) of 95.45 after the predialysis treatment at room temperature; these values were much higher than those of the commercial DF-120B membrane (0.004 m/h for U H 1 and 24.3 for S at 25 8C) and other reported DD membranes. QPAE-a has great potential for acid recovery via DD.