Multimodal spectroscopy and molecular dynamic simulations to understand redox-chemistry and compound formation in pyrometallurgical slags: example of manganese oxidation state with respect to lithium recycling

Pyrometallurgical slags are a valuable secondary resource for several technologically important critical materials/elements. A promising cost-efficient recovery currently under research depends on the incorporation of the element of interest into a specific compound. This new approach under research to recover these elements from the slag is called the "Engineered Artificial Minerals" (EnAM) concept. Optimization of slag system and cooling conditions potentially allow enrichment of a desired element in only one phase. Studying EnAM-formation requires multi model characterization of the slag at different states of formation. This includes bulk as well as microscopic elemental, structural, and species analytical tools and modeling approaches. Here, a characterization strategy mainly studying the formation of potential EnAMs for the recovery of lithium from battery recycling slags is reviewed. LiAlO2 as well as lithium manganates were identified as promising EnAMs. The manganese oxidation state was identified a decisive parameter. For a knowledge-based design of slags, it is necessary to understand the processes leading to oxidation state variability. Hence, besides structural, compositional characterization, speciation of redox active elements is discussed here using molecular dynamics simulations, powder X-ray diffraction, electron probe microanalysis, X-ray absorption near edge structure, micro-X-ray fluorescence, micro-X-ray diffraction, and micro-X-ray absorption near edge structure.