Pre-treatment operations: Reactive milling for the production of metallic black mass
During the second semester, researchers from KIT further studied and improved the conditions for the mechanochemical transformation of Black Mass (BM). With the BM supplied by ACC is already in a reduced state, the focus now shifts towards reducing the BM provided by partner TES.
This BM consists mostly of nickel-manganese-cobalt (NMC) cathode material and graphite, and it was found to cause a longer reaction time. It is expected that the graphite exfoliates during milling and creates thin protective layers around NMC particles and the reducing agent, slowing down the reaction kinetics.
Using variations of milling parameters like ball-to-sample ratio or the type and amount of reducing agent, researchers optimised the process towards the fastest kinetics. During the investigation, no intermediate reduction to transition metal oxides in lower oxidation states was observed. However, the full reduction of the respective part to the metallic composite occurred.
The operation took place in a shaker mill, and it requested an excess of 3.3 equivalents of Aluminium (Al) towards NMC was required to attain a complete reduction within a reasonable time. This transformation was accompanied by the formation of aluminium carbide and the presence of residual fine aluminium powder which caused a self-ignition hazard when the milled powder came into contact with air.
In contrast, when using calcium as a reactive agent, researchers observed a fast reaction but they also reported a strong dependency of reaction kinetics on calcium size. The hazard of self-ignition when exposed to air was limited in this case by using stoichiometric amounts.
In addition, the research team has been conducting preliminary experiments for the scale-up process using a planetary mill. It was observed that the choice of the milling type has a significant impact on the reaction kinetics. Attempts to crush calcium pieces proved to be unsuccessful, therefore not initiating any reaction. However, when using aluminium, reactions occurred much faster.
In the months ahead, the research team working in WP4 will continue to investigate the milling parameters for the planetary mill.
Find out more information about the activities developed in WP4 in the article Reactive milling for the production of metallic black mass (MBM) – Rhinoceros project (rhinoceros-project.eu)
Read more about the black mass leaching operations in the article Materials extraction and direct routes for the synthesis of electrode materials: Recovery of Lithium as battery grade materials