The modified Black Mass (BM) obtained in Task 4.4 – Reactive milling for the production of metallic black mass (MBM), as well as the BM supplied by partner ACCUREC (ACC) were leached under different conditions to extract lithium (Li) salt.
The BM provided by ACC consists of graphite, as well as transition metals such as nickel (Ni), manganese (Mn), cobalt (Co), along with their respective oxides and impurities – copper (Cu), iron (Fe), and few fluorinated compounds. Li is present in the form of lithium carbonate [Li2CO3] and lithium aluminium oxide [LiAlO2 ]. However, breaking off LiAlO2 to a soluble Li-salt and removing fluoride contamination is a challenging process. To overcome this, the BM was heated with calcium hydroxide in deionised water for one hour and then filtered.
Illustrated in the next figure, LiAlO2 decomposes during heating and transforms into insoluble calcium aluminium hydroxide. Dissolved fluoride anions are caught by Ca2+ ions and precipitate as calcium fluoride. The soluble part only contains Li- and Ca-salts. The latter can be transformed into calcium carbonate and removed with a second filtration step.
The second BM from partner TES, obtained after ball milling, consists of graphite, the metallic composite, lithium oxide and the oxidized reducing agent, along with some impurities like Fe and fluorinated compounds.
Lithium extraction after ball milling
In the aluminium system, the extraction of lithium salt poses certain challenges. Due to the tendency of residual aluminium powder to ignite when in contact with air, this requires cautious handling. During milling lithium aluminium oxide is formed, and in the basic solution, a significant amount of aluminium hydroxide dissolves and reacts with lithium hydroxide and CO2, resulting in the formation of a poorly soluble compound called LACHH. To address this problem, the suspension is heated to 90°C to reinforce the reaction between aluminium hydroxide and lithium hydroxide. The LACHH formed can be decomposed at 350°C into insoluble aluminium oxide and soluble lithium carbonate, which can be separated through filtration.
Lithium extraction in the calcium system, on the other hand, is a relatively straightforward process. The milled powder shows low reactivity towards both oxygen and water. Scientists successfully extracted 98% of lithium from the black mass; however, calcium hydroxide was also dissolved in the process. Subsequent purification steps led to the isolation of lithium carbonate with a purity of 93% in a yield of 75%. The main impurities are shown in the figure displayed below.
In the upcoming months, researchers will work to improve the leaching conditions towards a lower reagent and water consumption, while obtaining a higher purity of resulting lithium salt and lower lithium loses during purification steps.
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
Before MC processing, the black masses were analysed using a combination of different analytical techniques. Both quantitative and qualitative analysis were undertaken to determine the Lithium and transition metals yield of the developing recycling process.
Using different reducing agents such as Al, Ca, and their mixtures, researchers carried out preliminary investigations of the MC processing of BMs. Within this task, different aspects, such as the role of the ball milling conditions, the ball milling time, presence of other nonreactive components, and nature of the reducing material were investigated. The analysis led to the conclusion that the kinetics of the MC-induced reduction reaction is sensitive to multiple processing parameters, as shown in the featured image:
The upcoming research will focus on improving the reduction reaction kinetics and eliminating the possible safety hazards of fine powder materials. Once finalised, this work will determine the optimal ball milling conditions to be scaled up.
Recovery of Lithium as battery grade materials
The process described in Task 4.4 leads to the chemical transformation of the black masses (BMs) into ferromagnetic Co-, Ni- and Mn-containing products, which will be separated from other by-products. Lithium will be extracted from the rest of the solid products in the subsequent aqueous leaching process to be further transformed into battery-grade lithium carbonate (Li2CO3) salt.
Within the M1-M6 period, aqueous leaching of the ball-milled samples using Al and Ca as reducing agents (RA) was carried out. At a preliminary stage of investigations, researchers noticed the resulted Li2CO3 materials presented small amount of impurities.
To increase the yield of lithium recycling, in the upcoming period, the research work will target the improvement of the leaching conditions and the purification process.
TECNALIA [TEC] has actively undertaken both the coordination tasks and the experimental activities that correspond to the solvometallurgical treatment of the received black masses. Firstly, the coordination of the project started with the preparation of the kick-off meeting, in which the entire Consortium assembled in San Sebastián (Basque Country – Spain) and comprises administration and management to ensure an efficient development of RHINOCEROS project.
Also, the experimental section concerning the critical materials extraction from the received black masses from spent batteries started out after receiving the samples from partners ACCUREC [ACC] and KIT.
After characterisation, TEC performed a first round of tests to these samples using a solvometallurgical route and assessing pre-treatment effect on the process. In parallel, State of Art is analysed for different relevant solvometallurgical systems aiming lithium recovery. New batches of experiments will be performed for process optimisation and new tests will also be performed when further black mass samples are received.