Lithium-ion batteries recycling with froth flotation – A study on characterization and liberation strategies

Abstract

With the constant growth in portable electronic devices and the expected market growth for electric vehicles, the demand for lithium-ion batteries (LIBs) is booming. The raw materials production with a combination of mining and recycling will be essential and unavoidable to meet the upcoming demand for LIBs. Consequently, the European authority is updating the regulations demanding higher recovery efficiencies, 70 % by 2030. However, most of the state-of-the-art recycling technologies for LIBs focus on the recovery of components that have high economic value such as Co and Ni. The fine fraction resulting from the mechanical pre-treatment containing the lithium metal oxides (LMOs) and graphite particles, commonly referred to as "Black Mass" (BM), is generally used as a starting point for metals recovery by metallurgical means. Indeed, in industry, this BM is usually not further sorted and is directly fed to pyro- and/or hydrometallurgical processing routes to extract metals from LMOs, at the expense of graphite not being recovered. Recent studies, however, have convincingly illustrated that froth flotation can be applied to the BM to efficiently generate two valuable products, therefore increasing the overall efficiency of LIB recycling significantly. The work presented in this thesis aims to increase the overall materials recovery from LIBs by improving the BM beneficiation through froth flotation. The research work hereby presented offers a systematic study of the influence of the recycling pre-treatment processes on the liberation of the LIB components and the potential flotation mechanisms of active particles. The first part of this thesis is focused on the liberation analysis of the LIB components, which cannot be determined by conventional bulk characterization techniques such as X-ray fluorescence. In this thesis, a new approach for the BM characterization using automated mineralogy has been developed. With this particle-based technique, information on the chemical composition, morphology and degree of liberation of LIB components was acquired, helping to understand how the particles behaved during the process. The second part is focused on BM beneficiation on the basis of flotation. The use of flotation has recently gained interest as a method to separate LMOs and graphite particles. However, the flotation mechanisms of LMOs have not been paid sufficient attention. Therefore, this work provides the first fundamental study on the flotation mechanisms of active particles, with the aim of properly identifying the challenges to overcome in order to drive selectivity in flotation separation. To understand the flotation behavior, an industrial BM from pyrolyzed LIBs was compared to a model BM, comprising fully liberated LMOs and graphite particles. In addition, ultrafine hydrophilic particles were added to the flotation feed as an entrainment tracer, showing that the LMOs recovery in overflow products is a combination of entrainment and true flotation mechanisms. Ultimately, the findings of this thesis indicate the possibility of recovering and reusing graphite into new batteries.