Impact of different lixiviants on leach residue graphite during hydrometallurgical battery recycling

Recycling of graphite from Li-batteries has attracted increased interest due to the substantial increase in global demand. In this work, leach residues of different battery recycling solutions were characterized as one potential secondary source for graphite. Sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and sodium hydroxide were studied (2 M and 4 M concentrations, T = 60 °C, S/L = 100g/L, t = 3 h, V = 500 mL) to evaluate their impact on graphite purity and characteristics. Battery waste was industrial lithium nickel manganese cobalt oxide-rich (NMC) black mass. It was found that leaching with 4 M HCl achieved the highest removal of battery metals and resulted in the highest graphite purity (54 wt%) in the residue. Phosphoric acid was shown to cause in-situ precipitation of small MnPO 4 ·H 2 O and FePO 4 particles, whereas coarser Mn-rich particles precipitated during sulfuric acid leaching. All the studied lixiviants were found to maintain the structure of graphite as there was no significant increase in the defects or changes to the degree of graphitization. These results demonstrate that a typical hydrometallurgical leaching process alone is insufficient for graphite purification but requires additional purification and processing steps to valorize graphite. • Graphite residues were characterized after leaching in alternative lixiviants. • Highest graphite purity in leach residue was achieved with 4 M HCl leaching. • Residue impurities include mostly P, F, Si, Al, and C. • Leaching in H 3 PO 4 resulted in MnPO 4 ·H 2 O and FePO 4 precipitation residues. • All lixiviants studied only had a minor impact on the existing graphite structure.