Regeneration of NaOH from the Spent Na2SO4 Solution by Two-Compartment Bipolar Membrane Electrodialysis

With the recent introduction of various environmental policies focused on carbon neutrality has made recycling a crucial task in the electric vehicle industry. In particular, the recycling of lithium-ion batteries, a critical component of EVs, is becoming increasingly important. The process of recovering valuable metals such as lithium (Li), cobalt (Co), manganese (Mn), and nickel (Ni) from spent batteries typically involves leaching, precipitation, solvent extraction, and crystallization. However, these processes generate a significant amount of Na2SO4 wastewater. To address this issue, bipolar membrane electrodialysis (BMED) has been developed to recover H2SO4 and NaOH from Na2SO4. The conventional method uses a three-compartment configuration to simultaneously recover acid and base components, This approach, however has drawbacks such as high initial installation costs due to the expensive membranes and low current efficiency. To overcome these limitations, a two-compartment constant voltage method using cation exchange membranes and bipolar membranes was employed in this study. The effects of various process parameters on the recovery rate of NaOH, current efficiency, flux, and energy consumption were evaluated. Based on the optimal conditions from the experiment, a flow rate of 950 mL/min, a feed solution of 1.30 M Na2SO4 at 1.5 L, and an initial base solution of 0.1 M NaOH at 0.50 L resulted in an base recovery rate of 67.59%, with 0.91 L of 2.96 M NaOH recovered.