Series-connected hexacations cross-linked anion exchange membranes for diffusion dialysis in acid recovery

Abstract A series-connected tetracation cross-linker, DB, was synthesized successfully from 1,4-diazabicyclo[2.2.2]octane (DABCO) and dibromomethane. Which had two terminal tertiary amine groups and reacted with the bromomethylated poly(aromatic ether sulfone) (BPAES) based on 9,9-bis(4-hydroxyphenyl)fluorene and the other copolycondensation monomers giving a series of series-connected hexacations cross-linked anion exchange membranes, QPAES-DBs, for acid recovery by diffusion dialysis (DD). When applied in mostly reported simulated solution mixture of HCl and FeCl2, QPAES-DB50 shows the best DD performances with separation factor of H+ to Fe2+ ( S H + / Fe 2 + ) value of 127 and dialysis coefficient of hydrogen ion ( U H + ) value of 18.92 × 10−3 m/h, which are much higher than that of the commercial membrane TWDDA1 ( U H + = 9.18 ×10−3 m/h, S H + / Fe 2 + = 38.08). The phenomena are possibly resulted from the strengthened DONNAN effect provided by the crosslinking network containing series-connected hexacation segments at a certain crosslink density. In addition, the application in DD of QPAES-DB50 was extended to the multi-metals ions chlorides system of Mn2+/Ni2+/Cu2+/Cd2+/Cr3+. The separation factors of H+ to Ni2+, Mn2+, Cr3+, Cu2+ and Cd2+ reach up to 137.48, 119.90, 54.59, 32.84 and 16.19 separately. Evidently, QPAES-DB50 exhibits excellent DD performances and great potential of acid recovery.