Selective recovery of lithium carbonate from lithium-ion battery black mass through microwave-assisted carbothermal reduction and water leaching

This study investigates lithium recovery from lithium-ion batteries black mass using microwave-assisted carbothermal reduction followed by water leaching. Conventional hydrometallurgical processes often face challenges in lithium recovery due to low efficiency and impurities. The aim of this study is to evaluate the impact of microwave pre-treatment on lithium recovery efficiency, selectivity, and its economic and environmental viability. Lithium was leached from black mass samples in deionized water and recovered as lithium carbonate through direct evaporation. Results demonstrated that microwave pre-treatment improved lithium recovery when leaching temperature was 60 °C, with the highest yield after microwave pre-treatment (69.11 ± 8.58 %) and at 25 °C (65.02 ± 3.98 %). Direct water leaching achieved efficiency of 63.98 ± 4.30 % at 60 °C and 63.72 ± 1.34 % at 25 °C. Microwave pre-treatment followed by water leaching at 60 °C showed the highest purity in the recovered lithium carbonate (97.01 ± 0.53 %). A preliminary economic analysis revealed the highest operational costs with microwave pre-treatment at 60 °C (6.13 ± 0.60 €/kg of lithium carbonate equivalent, LCE), while the lowest were for direct water leaching at 25 °C (2.63 ± 0.13 €/kg LCE). The highest greenhouse gasses (GHG) emissions (10.23 ± 1.00 kg CO₂-eq/kg LCE) were related to microwave pre-treatment at 60 °C and the lowest (4.31 ± 0.79 kg CO₂-eq/kg LCE) to direct water leaching at 25 °C. In conclusion, even if it wasn't the most cost-effective and environmentally friendly option among the tested conditions, microwave pre-treatment improved lithium recovery efficiency and selectivity. Future research should aim at improving the technical performances of the process and at the same time at decreasing the operational costs and GHG emissions.