Recovery of Metals from Spent Lithium-ion Batteries Through Adsorption Processes Using Waste Materials

Abstract

The rapid growth in the use of lithium-ion batteries in electric vehicles and portable electronics has made their recycling a pressing global concern. The primary challenge is developing a universal, sustainable process capable of effectively treating diverse cathode chemistries, such as LiCoO₂ (LCO), LiMn₂O₄ (LMO), and LiNiₓCoᵧMn₁₋ₓ₋ᵧO₂ (NMC). This study has developed an integrated, environmentally friendly recycling method that incorporates thermal pretreatment, selective leaching, bio-based adsorption, and lithium recovery, making it suitable for all major cathode materials. Thermal treatment at 570 °C in air for 2 hours effectively removed the PVDF binder and organic residues, without forming unwanted cobalt oxides or metallic alloys, resulting in clean, reactive powders. Optimized leaching using a mixed citric–sulfuric acid system achieved almost complete metal recovery (Li, 99%; Co, 98%; Ni, 90%; Mn, 92%) under mild conditions, with citric acid acting as both a complexing and reducing agent, thereby eliminating the need for external reductants. The adsorption process was preferred over traditional separation methods because of its simplicity, low cost, high selectivity, and minimal secondary waste. Chitosan powder, a by-product derived from marine waste, exhibited strong affinity for Co(II), Mn(II), and Ni(II), while leaving lithium in solution. Crosslinking with 1 wt.% L-cystine produced stable CS1%CYS with increased porosity and mechanical strength, reaching adsorption uptake capacities of 153 mg/g for Co(II), 15.6 mg/g for Ni(II), and 7.7 mg/g for Mn(II), and maintaining over 92% recovery after multiple regeneration cycles with 0.1 M EDTA. Additionally, a greener version of chitosan was synthesized using the protic ionic liquid [Eth][Ac], showing similar adsorption performance to commercial powder while lessening environmental impact. Advancing toward practical application, fixed-bed column experiments demonstrated the scalability and stability of the beads under continuous-flow operation, with Co(II) and Ni(II) exhibiting strong retention and predictable breakthrough behavior. The residual Mn(II) was effectively removed (>86%) by KMnO₄ oxidation or pH adjustment, while Li can be recovered as Li₂CO₃ from the solution by reacting with saturated Na₂CO₃ at 90 °C. Comprehensive characterization techniques, including XRD, SEM-EDS, FT-IR, TGA, and BET, supported the results of each stage, confirming the complete removal of the binder, successful metal coordination through amine and hydroxyl groups, and an increased surface area of the modified chitosan. Overall, this study presents a universal, scalable, and sustainable methodology for the selective recovery of critical metals and battery-grade lithium carbonate from spent lithium-ion batteries, representing a significant advancement toward circular, low-carbon battery recycling.