Non-aqueous leaching of critical metals from black mass of spent lithium-ion batteries using a reusable acidic organophosphorus extractant

Recycling critical metals from the black mass of spent lithium-ion batteries (LIBs) is essential for supply security and waste management. Conventional hydrometallurgical acid leaching is effective but generates large volumes of wastewater. In this study, a non-aqueous leaching system has been developed using an acidic organophosphorus extractant, di-(2-ethylhexyl)phosphoric acid (D2EHPA), as the lixiviant, consolidating leaching and solvent extraction (SX) into a single stage. Metallic copper and aluminum were evaluated as reductants; only copper enabled effective leaching in D2EHPA. Key parameters (stirring speed, copper dosage, D2EHPA concentration, temperature, time, and pulp density) were optimized. The optimum was 700 rpm, 0.15 g Cu per g black mass, 2.0 M D2EHPA, 90 °C, 4 h, and 1.0 g black mass per 20 mL D2EHPA. Under these conditions, leaching efficiencies were ∼100 % for Li, 79.2 % for Ni, 94.6 % for Co, 47.3 % for Mn, and 96.4 % for Cu (reductant). D2EHPA was reusable over five leaching-stripping cycles with negligible performance loss. Metals were recovered from the loaded organic by (i) pH-controlled aqueous stripping and (ii) oxalic-acid precipitation stripping. The study also examined the potential of using copper-containing waste, such as waste printed circuit boards (WPCBs) and Cu-Al foil from spent LIBs as reducing agents, enabling an integrated waste-recycling scheme. This non-aqueous leaching process reduces unit operations and lowers chemical and water consumption while maintaining high recovery for key metals.