Chemical and mineralogical characterization of Li- and Mn-bearing slags to increase the recycling efficiency of lithium from lithium-ion-batteries (LIB)

Within the framework of the BMBF-funded project „PyroLith“ (FKZ: 03XP0336C), which deals with the recovery of lithium from NMC-type LIB via a combined pyro- and hydrometallurgical process route, two slag sample series of a simplified five-component system SiO2-Al2O3-CaO-Li2O-MnO were characterized using XRD, SEM-MLA, EPMA, XRF, ICP-MS and UVC radiation. The focus of the investigations was on crystalline and amorphous Li-bearing phases, their crystal growth and degree of intergrowth.

The results show that the slags generally solidified in a vesicular to compact, fine-grained, holo- to hypocrystalline, heterogeneous microstructure with a silicate matrix. Euhedral, anhedral and/or dendritic crystals up to 900 µm in size are embedded in the groundmass. In addition to variable contents of amorphous components, a total of six crystalline Li-containing phases (γ-LiAlO2, β-eucryptite, Li-Mn-Al spinel, LiAl5O8, Li5AlSi2O8, Li2MnSiO4) and two crystalline Li-free phases (melilite, glaucochroite) could be identified and quantified. Based on their chemical composition, two amorphous phases are distinguished. γ-LiAlO2, which is considered most important for an effective recovery of lithium in the selected process route, shows a characteristic green luminescence colour with distinct phosphorescence under short-wave ultraviolet radiation (254 nm). An influence of manganese on the crystallization of γ-LiAlO2, as described in [1] and [2], could not be observed.

[1] LIBRI (2011): Entwicklung eines realisierbaren Recyclingkonzeptes für die Hochleistungsbatterien zukünftiger Elektrofahrzeuge. Abschlussbericht, 132 S., Hanau

[2] Wittkowsi A., Schirmer T., Qiu H., Goldmann D. & Fittschen U.E.A. (2021): Speciation of Manganese in a Synthetic Recycling Slag Relevant for Lithium Recycling from Lithium-Ion-Batteries. Metals 2021, 11, 188