Selective separation of anode and cathode active materials from NCM-type spent lithium-ion battery black mass via interparticle interaction using humic acid

Flotation has emerged as a promising technique for the selective separation of anode and cathode active materials in the direct recycling of black mass (BM) derived from spent lithium-ion batteries (LIBs). However, the surface properties of BM are significantly altered by residual polyvinylidene fluoride (PVDF) binders and impurities, leading to particle aggregation. In addition, flotation is limited by the entrainment and entrapment of fine and ultrafine particles, resulting in reduced separation selectivity. In this study, Suwannee River humic acid (SRHA), a natural organic dispersant, was employed to regulate interparticle interactions and enhance flotation selectivity. Dispersion, zeta potential, and adsorption analyses revealed that SRHA had a negligible effect on pristine active materials but showed higher apparent adsorption onto heterogeneous BM surfaces, shifting the zeta potential from −22 mV to −47 mV and significantly improving dispersion stability. This surface modification induced both electrostatic repulsion and steric stabilization, effectively suppressing particle aggregation. Under optimized conditions (impeller speed of 1800 rpm, an SRHA concentration of 1 mg/L, a collector dosage of 150 g/t, and a frother dosage of 50 g/t), flotation achieved graphite and NCM grades of 86.81% and 85.64%, respectively. The grades were further enhanced to >90% for graphite and >97% for NCM through multistage flotation (cleaner and scavenger stages). These findings demonstrate that controlling interparticle interactions using a natural organic dispersant is an effective strategy to suppress entrainment and enhance flotation selectivity, providing a practical pathway for the high-purity recovery of active materials from BM and advancing direct recycling processes for LIBs.