A sustainable complexation leaching of critical metals from spent lithium-ion batteries by glycine in a neutral solution

To reduce the environmental footprint of hydrometallurgical processing of black mass from spent lithium-ion batteries (LIBs), a green leaching system based on glycine and sodium metabisulfite (Gly-SMS) was proposed. The leaching study demonstrated that the highest cobalt and lithium recoveries of 100 percent and 99.8 percent were achieved under optimal conditions. The leaching mechanism revealed that the dissolution of LiCoO2 in the Gly-SMS solution followed the shrinking core model. The apparent activation energies for cobalt and lithium were determined as 48.05 and 41.51 kJ/mol, respectively, indicating a surface chemical reaction controlling mechanism. The leachate was then processed by an acidification-precipitation technique with oxalic acid as the precipitant to remove cobalt. Glycine complexes with metal ions by zwitterionic ligand and recycles in the leaching-precipitation circuit, reducing the reagent cost. Compared to other studies, this leaching system has near-neutral operating conditions and is cost-effective, making it an economically viable alternative for treating cathode materials from spent LIBs. Background Rechargeable LIBs are crucial for clean energy, supporting decarbonization and the circular economy. Their usage is projected to grow in consumer electronics and electric vehicles over the next decade. Despite advancements in electrode materials, cobalt remains essential in cathodes due to its high energy density, low self-discharge, and ease of manufacturing. As LIBs reach end-of-life, they are a valuable secondary resource for critical metals like cobalt, nickel, and lithium, making battery recycling a key process to address climate change and strengthen critical metal supply chains [1]. Hydrometallurgy is the primary method for metal extraction from spent LIBs, with organic acids preferred over mineral acids for their selective leaching of cobalt and lithium, facilitating separation from aluminum and other impurities [2]. Glycine (NH2CH2COOH) is emerging as a green lixiviant due to its broad pH compatibility for forming metal complexes and its minimal environmental impact [3]. In this study, a novel Gly-SMS leaching system was used for metal extraction from LiCoO2 cathodes. Various reducing agents, including hydrogen peroxide (H2O2) and SMS, were explored to enhance cobalt dissolution. The Gly-SMS system demonstrated comparable efficiency and kinetics to conventional methods like H2SO4-H2O2 but with better operational conditions. Additionally, Co(II) separation from leachate was achieved through an acidification-precipitation method, making Gly-SMS a promising alternative for LIB recycling. Materials and methodology Reagent-grade LiCoO2 served as the raw material in preliminary tests to assess the feasibility of the Gly-SMS leaching system. Two black mass samples, with chemical compositions detailed in Table 1, were then used in confirmatory tests to validate the system’s efficiency. Leaching experiments were carried out in a beaker at a temperature of 80 °C, with cobalt and lithium concentrations in kinetic samples analyzed using an atomic absorption spectrophotometer. After leaching, residues were filtered, rinsed with deionized water and dried at ambient conditions for further analysis. Cobalt precipitation from leachate involved acidifying the filtered pregnant leach solution with sulfuric acid, followed by the addition of 0.5 M oxalic acid, agitating for one hour and conditioning at room temperature for three hours to complete the reaction. Cobalt-oxalate was obtained by filtration, and LiCoO2 powders (pre- and post-leach) were characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Solution chemistry of the leachate was further examined using thermodynamic studies, with Eh-pH diagrams for cobalt and lithium in the Gly-SMS system generated by Outotec HSC 9.0 software. Fig. 1 Effect of temperature on LiCoO2 dissolution using 0.5 M glycineand 0.5 M Na2S2O5 for (a) Co and (b) Li; (c) Arrhenius plot. Results and discussion This study investigated various parameters affecting LiCoO2 dissolution in the Gly-SMS leaching system. The optimal leaching conditions were determined as: 1.25 M glycine, 1.25 M Na2S2O5, solid-to-liquid ratio of 50 g/L, temperature of 80 °C, and leaching time of 180 min. Under optimal conditions, nearly complete extraction of cobalt and lithium was achieved, and corresponding metal concentrations in the leachate reached 26.7 and 3.0 g/L, respectively. Cobalt in leachate was separated using oxalic acid, with the ideal conditions identified as a Co(II)/OA ratio of 1:1.1, pH 2.0 and 80 °C temperature, achieving 99 percent cobalt removal. Notably, oxalic acid selectively removed cobalt with less than 1 percent lithium loss, validating its use for effective separation. Figure 1 shows the leaching behavior of Co and Li at various temperatures. Fig. 2 Eh-pH diagrams for (a) Co and (b) Li in Gly-SMS leaching systemat 25 °C (solid line) and 80 °C (dashed line); [Co] = [Li] = 0.2 M,[Gly] = [SMS] = 0.5 M. The leaching mechanism was explained by the shrinking core model. It revealed that cobalt dissolution followed a mixed control mechanism with significant fits for both surface reaction and boundary layer diffusion models. For lithium, leaching was best described by the surface chemical reaction and product layer diffusion models, suggesting that cobalt reduction actively supported lithium dissolution. Activation energies derived using the Arrhenius law were 48.05 kJ/mol for cobalt and 41.51 kJ/mol for lithium, highlighting that high energy input is needed for metal extraction from LiCoO2 and that dissolution is governed by surface chemical reactions in the Gly-SMS leaching system. Thermodynamic study (shown in Fig. 2) indicates that Co(gly)₂ is the predominant cobalt species, while lithium remains largely uncomplexed, staying as free ions across a wide pH and Eh range, with the dissolution reaction: 4LiCoO2 + 8NH2CH2COOH + Na2S2O5 → 2Li2SO4 +4Co(NH2CH2COO)2 + 2NaOH + 3H2O (1) SEM-EDS analysis verified leaching efficiencies and examined precipitate composition by comparing untreated LiCoO2 (smooth, spherical particles 4 to 6 μm in size) with residues R1 (0.3 M SMS) and R2 (1.0 M SMS) post-leaching (as displayed in Fig. 3). Sample R1 showed reduced particle size and sharp edges, indicating partial dissolution due to limited reductant, while sample R2 exhibited larger cubic particles (about 5 μm in size) with smaller irregular ones. EDS mapping revealed uniform cobalt and sulfur distribution in R2, with oxygen and sodium concentrated in irregular particles, suggesting the formation of CoSO4, and lithium coprecipitation with Co and Na sulfate salts was inferred from metal recovery at high reductant dosage. Fig. 3 SEM images of (a) LCO, (b) sample R1 and (c) sample R2. Figure 4 illustrates the leaching and acidifying precipitation process, highlighting the unique advantage of the Gly-SMS leaching system’s near-neutral pH, which is higher than the acidic conditions typically required for organic acid leaching. Conventional organic acid leaching demands high acid concentrations to act as both proton donors and complexing agents. In contrast, the Gly-SMS system achieves rapid leaching and high metal recovery with near-stoichiometric glycine use, enabling efficient complexation with dissolved metal ions. The recyclability of glycine throughout the hydrometallurgical process significantly reduces reagent costs, given its minimal consumption. Fig. 4 Schematic diagram of LiCoO2 recycling in the Gly-SMS system. Conclusion This study presents a sustainable Gly-SMS leaching system for recovering cobalt and lithium from cathode materials. Under optimized conditions (1.25 M glycine, 1.25 MNa2S2O5, 5 g/L solid-to-liquid ratio, 80 °C, 180 min), the system achieved nearly complete cobalt (100 percent) and lithium (99.8 percent) extraction, producing concentrations of 26.7 g/L Co and 3.0 g/L Li in the leachate. Cobalt was efficiently isolated as cobalt oxalate via acidification-precipitation. Kinetic analysis using the shrinking core model revealed apparent activation energies of 48.05 kJ/mol for Co and 41.51 kJ/mol for Li, indicating a surface chemical reaction-controlled leaching process. SEM analysis showed that lower Na2S2O5 concentrations led to incomplete dissolution, while higher concentrations increased ionic strength, resulting in precipitate formation. Notably, the Gly-SMS system operates in a near-neutral pH environment (pH 6), with glycine forming stable, recyclable metal-glycinate complexes with minimal glycine consumption, highlighting this method’s environmental and economic potential for LIB recycling. Selected references Golmohammadzadeh R, Faraji F, Rashchi F (2018) Recovery of lithium and cobalt from spent lithium ion batteries (LIBs) using organic acids as leaching reagents: A review. Resour Conserv Recycl 136:418–435 Gao W, Liu C, Cao H, Zheng X, Lin X, Wang H, Zhang Y, Sun Z (2018) Comprehensive evaluation on effective leaching of critical metals from spent lithium-ion batteries. Waste Manag 75:477–485. Eksteen JJ, Oraby EA, Tanda BC (2017) A conceptual process for copper extraction from chalcopyrite in alkaline glycinate solutions. Miner Eng 108:53–66

A sustainable complexation leaching of critical metals from spent lithium-ion batteries by glycine in a neutral solution

Authored by: Jiajia W, Junmo Ahn and Jaeheon Lee

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