Integrating pyro- and biohydrometallurgy in a green closed-loop lithium-ion battery recycling approach

State-of-the-art stand-alone recycling routes for lithium-ion batteries (LIB), such as pyrometallurgy or hydrometallurgy, face significant challenges, including high energy consumption, loss of valuable elements like lithium (Li) and susceptibility to a waste stream with varying cathode chemistry. The present work investigates the comparison of recovery targets when processing synthesized black mass between a standalone biohydrometallurgical process and a combined method, including an upstream pyrometallurgical process. In this approach, black mass undergoes carbothermic reduction in the InduMelt reactor, in which volatile elements like Li are vaporized and extracted via the gas stream, producing a Li-free alloy. Thermodynamic equilibrium calculations using FactSage™ showed the possibility of partial oxidation when using the alloy in an open-loop approach. Within a closed-loop approach, the alloy was pulverized for downstream biohydrometallurgy. Bioleaching experiments using adapted enriched cultures with synthetic pre- and untreated NMC811 and LFP black mass were performed at pulp densities (w/v) of 1 % and 10 %. The highest leaching efficiency of up to 100 % for Nickel (Ni), Manganese (Mn), Cobalt (Co), and Aluminium (Al) was achieved in the 1 % pre-treated experiment. Increasing the pulp density to 10 % reduced the leaching efficiency of these metals to less than 25 % which could be attributed to factors such as the alkaline nature of the black mass, microbial inhibition and passivation due to precipitation. Pyrometallurgical pre-treatment improved metal leaching from NMC by up to 90 %, but had no impact on LFP. To close the materials loop, selective precipitation was applied.