Facile fabrication of high-performance porous anion exchange membranes for acid recovery from rare earth stripping solutions via diffusion dialysis

In the context of sustainable rare earth hydrometallurgy, the generated high-acid-content stripping solution represents a valuable secondary resource rather than a waste stream. Diffusion dialysis (DD) technology based on anion exchange membranes (AEMs) offers an energy-efficient and environmentally benign approach for acid recovery. However, the development of AEMs with simultaneously high acid permeability and excellent rare earth ion rejection remains a major challenge due to the intrinsic permeability-selectivity trade-off. Herein, a facile membrane fabrication strategy integrating nonsolvent-induced phase separation (NIPS) and one-step modification method is proposed to construct porous AEMs with tunable microstructure and enhanced diffusion dialysis performance. A chloromethylated polysulfone (CMPSF) porous substrate membrane was first prepared via NIPS and subsequently modified using N,N,N′,N″,N″-pentamethyldiethylenetriamine as bifunctional reagent, enabling simultaneous quaternization and crosslinking in a single step. The resulting hierarchical porous architecture, combined with a robust crosslinked ion-transport network, effectively promotes proton transport while suppressing the diffusion of rare earth ions. Consequently, the optimized porous PPSF-3 AEM exhibits an outstanding proton dialysis coefficient (40.4 × 10 −3  m h −1 ) and an excellent proton/rare earth ion selectivity ( S H + / La 3 + ${\mathit{S}}_{{\mathbf{H}}^{+}/{\mathbf{La}}^{\mathbf{3}+}}$ of 3231.9), which are 9.4 times and 5.7 times higher than those of the commercial DF-120 AEM, respectively. This enhanced separation performance is attributed to the synergistic effects of increased free volume, optimized ion-conduction pathways, and strengthened Donnan exclusion arising from the tailored porous-crosslinked structure. This study provides a simple and cost-effective strategy in fabricating high-performance porous AEMs for efficient acid recovery from rare earth stripping solutions through diffusion dialysis.