A Study on the Recycling of Sodium Citrate (Na₃Cit) Waste Solution via Bipolar Membrane Electrodialysis

Citric acid-based leaching is gaining attention as an environmentally friendly alternative to conventional sulfuric acid-based processes for recycling spent lithium-ion batteries (LIBs), but it generates sodium citrate (Na₃Cit)-rich wastewater that is difficult to treat using conventional technologies. Bipolar membrane (BM) electrodialysis (BMED), particularly a two-compartment BM/cation-exchange membrane (CEM) configuration, offers a simple and energy-efficient solution for simultaneously recovering acids and bases from such wastewater without external reagents, enabling a closed-loop resource-circulation approach that remains largely unexplored for this specific waste stream. This system was applied to treat Na₃Cit wastewater generated from citric acid-based spent LIB leaching, and the recovery feasibility and process performance of citric acid and NaOH were evaluated. The effects of feed concentration, current density, initial base concentration, and initial base volume on NaOH recovery, current efficiency, and energy consumption were investigated. Under the optimal conditions (1.00 M Na₃Cit, 300 A/m², 0.1 M NaOH, 1.25 L), a NaOH recovery of 93.93%, current efficiency of 92.55%, and energy consumption of 0.65 kWh/kg were achieved. This study demonstrates that Na₃Cit wastewater can be treated via BMED without external reagents, yielding high-purity NaOH, whereas the recovered acid stream contains residual unreacted Na₃Cit, and its direct reuse in the leaching process requires further verification. These findings provide a fundamental basis for developing BMED-based resource-circular processes.