Evaluation of a Bio-Based Solvent Pretreatment for Sustainable Froth Flotation of Black Mass from Spent Lithium-Ion Batteries.

Abstract

Froth flotation effectively separates anode graphite from cathode active materials (CAMs) of spent lithium-ion batteries when CAM particles are free of organic binders, such as polyvinylidene fluoride (PVDF). This study investigated a bio-based solvent, dihydrolevoglucosenone (Cyrene^TM ), as a pretreatment to remove the PVDF binder from both single chemistry black mass (BM) and industrially produced mixed chemistry black mass (IBM). The subsequent flotation combined with high-intensity attritioning improved CAMs and graphite separation efficiency compared to that of mechanical pretreatment alone, increasing from 0.30 to 0.53 in BM and from 0.37 to 0.54 in IBM. Although pyrolysis resulted in higher separation efficiencies of 0.92 in BM and 0.78 in IBM, Cyrene pretreatment presents advantages in non-emission of toxic gases and in preserving lithium within the CAMs. In the flotation process water, an average lithium dissolution of only 5.5% in BM and 14.7% in IBM was recorded with Cyrene pretreatment, compared to that of 29.3% in BM and 55.4% in IBM with pyrolysis pretreatment. The lower quality of the flotation products obtained with Cyrene pretreatment necessitates further purification steps such as cleaner flotation. Optimizing pretreatment parameters is crucial, including the Cyrene to black mass ratio and contact time. A key challenge is preventing the thermally induced phase separation of PVDF at temperatures lower than 80 °C, which negatively affects the effective separation of graphite and CAMs by froth flotation.