Effective fractionation of NH4+ and Mg2+ from rare earth tailings leachate for sustainable resource recovery by selective electrodialysis with multistage ionic sieving

Rare earth tailings leachate, enriched in ammonium sulfate and magnesium sulfate, poses considerable environmental challenges while representing a valuable source of recoverable resources. Herein, a selective electrodialysis (SED) process was developed for the selective separation and recovery of NH 4 + and Mg 2+ from nutrient-rich tailings leachate. The influences of feed concentration, concentrate-to-diluate volume ratio, and current density on ion migration, separation efficiency, permselectivity, and energy consumption were systematically examined. Increasing the current density from 5.5 to 7.5 mA cm −2 promoted NH 4 + transport, resulting in an increase in NH 4 + recovery from 49.1% to 90.2% and NH 4 + /Mg 2+ permselectivity from 59 to 361. To overcome the limitations of single-stage separation, a three-stage ionic sieving configuration was subsequently implemented to enhance monovalent/divalent cation discrimination. The improved process achieved the production of high-purity (NH 4 ) 2 SO 4 and MgSO 4 with purities of 99.8% and 97.9%, respectively. These results demonstrate that coupling selective electrodialysis with multistage ionic sieving effectively intensifies monovalent/divalent cation separation and enables efficient resource recovery from complex industrial effluents. The proposed strategy offers a promising and sustainable solution for rare earth wastewater treatment and salt valorization.