ION-IMPRINTED POLYMERS AS A SUSTAINABLE STRATEGY FOR THE EFFICIENT RECOVERY OF LITHIUM IONS FROM DILUTE SOLUTIONS

Lithium is a critical raw material with unique electrochemical properties, making it indispensable for the production of lithium-ion batteries (LIBs), which are widely used in portable electronics, electric vehicles, and energy storage systems. The growing demand for lithium, combined with the limited efficiency of current recovery methods, highlights the urgent need for more sustainable and selective strategies. Nowadays, conventional recycling processes are energy-intensive, involve large amounts of chemicals, and recover less than 10% of lithium in Europe. This PhD research investigates the use of ion-imprinted polymers (IIPs) as an innovative solution for lithium recovery from dilute aqueous solutions. A novel approach based on pseudo-crown ether chemistry was developed, utilizing poly(ethylene glycol) diacrylate (PEGDA 575) as a unique bifunctional component acting both as functional monomer and cross-linker, thus avoiding the use of expensive and potentially hazardous crown ethers. Several polymerization strategies were tested, with bulk polymerization providing the most promising results in terms of lithium adsorption efficiency and selectivity. The IIP synthesized in DMSO demonstrated excellent performance, reaching a theoretical lithium adsorption efficiency of 86%, a recovery rate of 85% using sodium carbonate (Na₂CO₃) as the desorption agent, and a binding capacity of 1.37 mg·g⁻¹. These properties were maintained when the polymer was applied to simulated battery leachates, confirming its selective recognition and efficient adsorption of lithium ions even in multi-component systems. Moreover, the polymer retained its performance over multiple adsorption–desorption cycles, demonstrating reusability and structural stability. However, when applied to highly acidic environments, such as 2% nitric acid solutions, a sharp reduction in adsorption efficiency was observed, with a theoretical lithium adsorption of approximately 10%, which remained consistent also in simulated acidic leachate samples. This suggests that while the IIP system performs well in neutral or weakly acidic environments, its performance significantly drops in strongly acidic media. Consequently, to efficiently apply this polymer in practical scenarios, especially when dealing with leachates obtained from hydrometallurgical treatments of spent LIBs, a neutralization step is currently required to adjust the pH before the adsorption process. Structural characterization by FTIR, solid-state NMR, SEM, and BET confirmed the formation of lithium-specific binding sites and the polymer’s robust morphology. Fixed-bed column experiments highlighted some limitations in continuous flow systems, mainly due to reduced contact time and flow distribution issues, but indicated potential application in pre-concentration processes. Overall, this research demonstrates that PEGDA-based IIPs represent a sustainable, low-cost, and reusable material for lithium recovery, especially from complex aqueous matrices, provided that a pH adjustment step is integrated into the process design to optimize adsorption performance.