An Investigation of Flotation Separation of Lithium-Ion Batteries Mixed Cathodes and Anodes Powders

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Traore, Noufou
Spent lithium-ion battery , Natural graphite , Direct recycling , Flotation , Pretreatments
As part of the circular economy, the end-of-life batteries need to be recycled which will positively impact the environment and reduce energy consumption and slow the depletion of the natural resources. A closed-loop recycling known as Direct recycling involves physical treatment for the separation of mixed electrodes and has simplicity, low energy consumption, and lower environmental footprints compared to the pyro and hydrometallurgy processes which exhibit some environmental and economic limitations. Flotation falls under direct recycling and takes advantage of the difference in wettability between electrode materials (graphite and metal oxides) of the lithium-ion-batteries (LIBs). Fundamental studies on LIBs wettability and two natural graphite samples were investigated. The wettability range (∆γ) of LIBs is 20 mN/m compared to 18 and 28 mN/m for vein graphite (VG) and amorphous graphite (AG) respectively. The critical surface tensions of wetting of LIBs, VG and AG are respectively 31, 39, 59.5 mN/m suggesting high hydrophobicity degree and homogeneity of LIBs in comparison to AG due to the presence of organic coatings on the surface of black mass. After only 6 min of batch flotation, about 90% of the LIBs powder was recovered in the presence of 364 g/ton kerosene and 471 g/ton of MIBC. In spite of this high recovery, the upgrading ratio remained as low as 1.3-1.5 suggesting a lack of selectivity. This poor selectivity is again caused by the surface similarities between graphite and metal oxides as a result of the organic coating. All the treatments available in the literature to remove the organic coating and promote selective flotation have been studied where roasting was identified as the most effective variable with collector addition, leading to graphite recoveries above 95% and grades exceeding 90% in the rougher-scavenger stage. Two designs of experiments reveal their significant impact on flotation performance. The factors studied were roasting temperature and time as well as kerosene dosage where the temperature was identified as the most important main effect. A verification run at the optimum conditions suggests good agreement between the model estimate and the experimental results at the 95% confidence region.
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