Characterization and beneficiation of pyrolyzed black mass from spent lithium ion batteries

The lithium-ion battery (LiB) market is growing rapidly which leads to a considerable increase of LiB wastes. Despite the enhancement in graphite consumptions, there is no graphite recycling process from LiBs so far. Thus, graphite usually remains in slags from the metallurgical treatments.
The LiB components contain cobalt (Co), lithium (Li) and graphite, counted as critical materials. The aim of the present thesis is to increase the recycling recovery of the LiBs by developing a new innovative process, which minimizes metal losses and is able to recover graphite. By using flotation two valuable products, one of graphite and one with the valuable metals, are recovered in the light of their integration to the value chain of LiB production.
Mineral liberation analysis (MLA), x-ray fluorescence (XRF) and x-ray diffraction (XRD) were used for characterization of the black mass to understand the liberation behavior of the crushed LiB particles. Flotation tests were carried out in an Outotec GTK Labcell, the main studied parameters are the pre-treatment with attritioning, the flotation pH and the reagents dosages. Kerosene was used as a promoter for graphite and MIBC as a frother.
It was found that graphite particles were fully liberated from the copper foils, and the organic layer on the active particles was removed which increases the separation efficiency. However, only 62 wt. % of the cathode active particles are liberated from the aluminum foil. Based on this characterization results, particularly the liberation degree, a new flowsheet is designed to concentrate all the active material (graphite, Co, Ni, Mn and Li) in the < 50 μm fraction without current foil particles. Flotation studies show that pretreatment, such as attritioning, improved the process efficiency while preserving the spherical shape of graphite. Graphite recovery is +98 % with a grade of 72 wt. % and the tailings recover more than 90% of the precious metals Co, Ni and Li from the spent LiBS, with the respective grades 27 wt. % Co, 7 wt. % and 2.5 wt. % Li. Most of the concentrate impurities are fine particles from cathode active materials, which could be removed with a desliming process and flotation cleaner stages. This research is at its beginning and is expected to bring about an innovative and useful process for the recycling industry, despite the challenges involved. This process can recover the graphite and the lithium, which are usually ending the slags. At present, there might be legitimate questions regarding the expense and benefits of graphite recycling. However, the treatment of LiBs will become necessary in the near future due to environmental issues as well as the scarcity and criticality of LiB components. Consequently, graphite will become a valuable and needed by-product from the metals recycling. The dependence on imports of graphite from China would be reduced, providing a solution to meet the significant predicted demand of battery grade graphite. Moreover, LiB as a key driver of the transition away from a carbon-based economy, it is necessary to ensure a truly positive impact over the lifecycle of LiB, and consequently to reach a closed-loop system.