Performance Analysis and Optimization of a Membrane Capacitive Deionization Process for Lithium Enrichment from Lithium-Ion Battery Wastewater

The rapid growth of lithium-ion battery (LIB) manufacturing has increased the generation of wastewater containing lithium and transition metals, creating a need for selective recovery processes with minimal chemical use. This study evaluated membrane capacitive deionization (MCDI) with a monovalent-selective cation-exchange membrane (MS-CEM) for lithium enrichment from simulated LIB manufacturing wastewater. One-factor-at-a-time experiments and response surface methodology were used to identify key operating parameters and optimize their interactions. Under the optimized conditions (1.43 V, pH 4.48, sorption time 500 s), the system achieved a lithium enrichment factor of 2.54 and a Li+/M2+ selectivity coefficient of 4.71. Over 100 cycles (approximately 28 h), these values decreased to 2.15 and 2.17, respectively. SEM–EDS detected Ni-, Co- and Mn-containing deposits on the spacer, electrodes and ion-exchange membranes, consistent with transition-metal fouling, although the deposit phases were not determined. A single cleaning with 0.01 M EDTA followed by 0.01 M HCl restored the selectivity coefficient to 4.38 and the enrichment factor to 2.25. These results indicate the potential of MS-CEM-assisted MCDI as a selective lithium pre-concentration step prior to hydrometallurgical recovery and identify selectivity loss, which coincided with transition-metal deposition, as the main limitation to sustained operation.