An integrated electrodialysis with bipolar membranes (EDBM) process for acid and base recovery from spent ion-exchange regenerants

This study presents a novel process configuration for acid and base recovery from spent ion-exchange regenerants using electrodialysis with bipolar membranes (EDBM). Unlike conventional approaches that treat combined waste streams and require extensive pretreatment, our system processes the spent anion- and cation-exchange regenerants in two sequential EDBM units. Critically, the acidic effluent from the first unit is fed into the base compartment of the second unit, providing intrinsic pH regulation. This design effectively mitigates two major challenges in regenerant recycling: scaling caused by divalent cations and nitrate contamination of the acid product. Laboratory experiments and ion transport calculations demonstrate that the process achieves high recovery rates, reclaiming 90 % of Na+ from the anion-exchange regenerant and 69 % of Cl− from the cation-exchange regenerant, while producing high-purity NaOH (99.0 %) and HCl (98.8 %) at concentrations suitable for reuse (∼1 M). The integrated configuration reduces the salt content of the waste stream by 44 % and minimizes the need for neutralization chemicals. Our techno-economic evaluation shows that the process can be commercially viable under favourable cost scenarios. This approach offers a sustainable alternative to conventional regenerant disposal and may enable broader application of EDBM to industrial brines with challenging compositions.