Abstract
Spent lithium-ion batteries (LIBs) represent an increasingly important secondary source of Li and critical metals. In this study, Li and Co recovery were investigated through a combination of organic acid leaching, ion-exchange (IEX) resins, and precipitation methods. Oxalic acid demonstrated selective Li and Co leaching and precipitation of Co as CoC2O4(s) when heated to a supernatant, whereas citric acid provided similarly effective Li and Co leaching. IEX experiments compared the performance of three sulfonic acid cation-exchange resins, Amberlite IR120, Rexyn 101, and Amberlite HPR1100, under pH-controlled conditions. In ~250 mL synthetic citric acid leachates containing 0.5 M as citric acid and 937.8 mg/L as Li+, contact with 5 g of IR120 or Rexyn 101 reduced Li+ concentrations to 670.8 and 659.7 mg/L, respectively, demonstrating comparable removal of 28.5% and 29.7%, respectively. To those 670.8 and 659.7 mg/L as Li+ solutions, contact with 10 g of fresh IR120 or Rexyn 101 reduced Li+ concentrations to 344.8 and 395.1 mg/L, respectively, demonstrating comparable removal of 48.6% and 40.1%, respectively. In a 500 mL mixed Li/Co solution initially containing 230 mg/L as Li+ and 1900 mg/L as Co2+, 15 g of once used and regenerated Chelex® 100 reduced concentrations to 237 mg/L as Li+ and 639 mg/L as Co2+ followed by HPR1100, which achieved 130 mg/L as Li+ and 308 mg/L as Co2+. Resin regeneration using NaCl solutions enabled measurable desorption, with up to 324 mg/L as Li+ and 788 mg/L as Co2+ recovered in some regenerant solutions. Preliminary precipitation trials using ammonium fluoride showed that Li recovery is feasible but difficult to reproduce and strongly dependent on the Li:F molar ratio and pH. Thermodynamic modeling of aqueous speciation confirmed the formation of stable Co–oxalate and Li–citrate complexes, providing insight into observed recovery efficiencies. Collectively, these results along with others demonstrate the feasibility and practical limitations of integrating mild organic acids, IEX separation, and precipitation for closed-loop LIB recycling. The combined process shows promise as a low-energy, regenerable, and environmentally friendly alternative to conventional hydrometallurgical methods, while highlighting key areas for optimization at pilot scale.