Process-Oriented Characterisation of Black Masses from Li-Ion Batteries

Following countless Li-ion batteries capacity deployment announcements, the efforts on the recycling of these (end-of-life) products have been recently intensified in Europe, with a focus on Ni, Co, Mn and, at a lesser extent, Li, Cu and graphite recovery. Most current developments include a hydrometallurgical step, with or without a thermal pretreatment, on the so-called black mass. However, these processes tend to settle for a sole chemical analysis of the black mass and barely confront their robustness by feeding black masses differing in composition and/or pretreatment, although these have proven to impact the leaching performances and reagents requirements. This study aims at reinforcing the understanding of black masses behaviours through a systematic process-oriented characterisation using both physical (drying, PSD, magnetic separation, and XRD), chemical (ICP-OES, granulochemical distribution, XRF and TC) and microscopical (optical microscopy and SEM – EDS and Mineralogic) techniques on the process feed and leaching residue. Several industrial black masses have been comprehensively analysed and leached. Links between the composition, identified phases morphology and liberation degree, elements speciation and oxidation/pre-reduction levels, and the leaching performances have been established. As expected, thermally pretreated black masses exhibited some reduced phases of the transition metals (down to the metallic state), and thus required less reductive agents for the leaching than mechanical black masses. In parallel, occurrences of metals alloying could partially explain some leaching recalcitrancy. These results are in line with some previous authors’ empiric deduction and could strengthen their interpretation. All in all, this process-oriented characterisation scheme coupled with leaching experimentation opens doors to a better black mass leaching system comprehension, behaviour and upstream reagents prediction, regardless of the black mass chemistry or pretreatment.