Treatment of Na2SO4-Containing Wastewater Generated During the Recycling of Spent Lithium-Ion Batteries: Comparative Study on the Operating Modes of Bipolar Membrane Electro-Dialysis

The recycling of spent lithium-ion batteries generates Na2SO4-containing wastewater, resulting in environmental problems and resource losses. This study investigates a treatment method employing bipolar membrane electrodialysis (BMED) to recover H2SO4 and NaOH from such wastewater. The acid and base recovery efficiencies, energy consumption, operational stability, and economic feasibility of two BMED configurations, i.e., two- and three-compartment systems, were systematically compared. The current density, initial concentrations of the feed, and initial concentrations and volumes of the acid and base were optimized under constant current conditions. The three-compartment system exhibited higher acid purity and stability, whereas the other system exhibited lower energy consumption and membrane degradation. Under optimal conditions, both systems successfully recovered H2SO4 and NaOH from the Na2SO4-containing wastewater. A techno-economic analysis based on a lab-scale process revealed that the two-compartment system exhibited cost effectiveness while the three-compartment system showed long-term operational stability. These findings suggest that BMED is a viable and effective solution for the treatment of Na2SO4-containing wastewater generated from battery recycling processes.