Gluconic Acid Leaching of Spent Lithium-Ion Batteries as an Environmentally Friendly Approach to Achieve High Leaching Efficiencies in the Recycling of NMC Active Material

Organic acids, such as gluconic acid, have been widely studied for their potential in the hydrometallurgical recycling of lithium-ion batteries. These organic alternative leachants offer several environmental and recycling-related benefits, including a high selectivity in terms of dissolving valuable metals, as well as a reduced environmental impact due to the application of non-toxic and biodegradable organic acids. Gluconic acid has previously been demonstrated in the oxidative degradation of glucose, either as an alternative reducing agent or in biometallurgical approaches, and has been described as an efficiency-supporting reagent. The results of this study demonstrate the effectiveness of using gluconic acid for the recovery of metals such as lithium, cobalt, nickel, and manganese from spent lithium-ion batteries. Recovery rates of above 98% for lithium, cobalt, and manganese, and a recovery rate of more than 80% for nickel could be reached by optimizing the leaching parameters, including an acid concentration of 1.2 M, the addition of hydrogen peroxide of 1.6 vol %, a solid-to-liquid ratio of 25 g/L, a leaching temperature of 75 °C, and a leaching time of 192 min. These results show that gluconic acid has the potential to become a viable and sustainable option for the hydrometallurgical recycling of lithium-ion batteries, as well as for opening a possible biohydrometallurgical route. Further investigations are required into the results obtained, to verify the existence of a new hydrometallurgical and sustainable process route involving gluconic acid.