Effect of leaching reductants on the environmental impacts of an advanced hydrometallurgical battery recycling process

Use of hydrometallurgical lithium-ion battery recycling methods are gaining ground as the amounts of electric vehicle battery-related wastes that require treatment are growing. In this work, the environmental impacts of choosing either hydrogen peroxide or the copper-iron pair as the leaching reductant for nickel-manganese-cobalt oxide (NMC) black mass was investigated through process simulation-based life cycle assessment (LCA). Climate change burdens of the Baseline scenario, using hydrogen peroxide as the leaching reductant, were approximately 4.6 t CO₂-eq./t recycled black mass, while the savings from avoided primary production of the recovered metals were approximately 13.0 t CO₂-eq./t recycled black mass. Use of copper and iron as leaching reductants resulted in reduced climate change burdens and savings of 4.4 and 13.1 t CO₂-eq./t recycled black mass, respectively. Results show that hydrogen peroxide has some contribution to the environmental impacts of the proposed recycling process and its replacement with the copper-iron pair shows limited environmental benefits. Although replacement of peroxide reduces, e.g. the climate change impacts of the leaching step by approximately 75 %, an overall reduction in the total impacts of the process remain inconclusive. The difference in leaching impacts between the two scenarios was found to be small when compared to the total scale of environmental savings, with hydrogen peroxide climate change impacts being approximately 77 % of the leaching burdens in the Baseline scenario, but only roughly 12 % of the total burdens, and approximately 5 % of the savings obtained from nickel and cobalt recovery. Furthermore, the economic feasibility of using copper – which is classified as a strategic raw material – to provide the reductive power in leaching can be questioned. Conversely, use of soda ash for lithium recovery was determined to be a major source of burdens, leading to approximately three times the climate change impacts of those from hydrogen peroxide use, and covering approximately 35 % of the total climate change burdens in the Baseline scenario. The results provide details of environmental burdens and savings in the rapidly developing area of hydrometallurgical battery recycling and highlight potential optimization areas for emerging recycling operations.