Microwave low-temperature treatment – Step leaching process for recovering black mass from spent lithium-ion batteries

Cathode materials in the black mass from spent lithium-ion batteries can be efficiently reduced using microwave treatment. However, the interaction of different components in the recovery process has not been fully understood. The study aims to reveal the influence of impurities on the recovery of valuable metals using microwave low-temperature roasting and step leaching, realizing the separation of impurities and valuable metals. The sample black mass containing impurities was obtained by industrial dismantling process. The mechanisms of microwave-enhanced reduction were revealed by studying the dielectric properties and thermal evolution of different elements. Dielectric loss tangent increased with temperature and reached a peak value of 0.12 at 550 °C, facilitating microwave absorption and reduction reactions. The cathode materials were reduced efficiently in a semi-closed microwave system without inert atmosphere. The impurities graphite, Al and organics (electrolyte and PVDF) were potential in-situ reducing agents. The reduction products consists of Li2CO3, CoO(Co) and a small amount of LiAlO2, LiF and CoF2. The co-leaching of Al and Co was observed during the carbonated water leaching for recovering Li2CO3, which can be precipitated as Co6Al2CO3(OH)16·4H2O by aging of the leachate. Al in the water leaching residue was effectively removed using alkali leaching of 6 M NaOH. Finally, Co was selectively leached without dissolution of Cu by 2 M H2SO4. The optimized process parameters were obtained. The research results may provide technical guidance for the efficient recovery of industrial black mass. [Display omitted] •Reduction and pyrolysis of industrial black mass were strengthened by microwave.•The microwave absorption properties of black mass reached a peak at 550 °C.•Impurities especially aluminum were both reducing agents and harmful substances.•The co-leached Co and Al were precipitated to Co6Al2CO3(OH)16·4H2O for removal.•Step separation of lithium, aluminum, cobalt and copper/graphite was achieved.