Green mechanochemical activation for acid-free recovery of valuable metals from spent lithium-ion battery sulfide residue

Abstract

Recovering critical metals such as nickel, cobalt, and lithium from spent lithium-ion batteries is vital for maintaining a sustainable resource supply. The sulfidation process enables efficient selective lithium extraction from black mass, but simultaneously generates dense and highly crystalline polymetallic sulfide residues. These secondary resources of nickel and cobalt exhibit high chemical stability, posing significant challenges for further processing under conventional extraction conditions and severe environmental pollution risks. This study addresses the refractory nature of sulfide residue through sulfur-assisted mechanochemical activation pretreatment, followed by an innovative and environmentally friendly oxygen-pressure water leaching process to extract valuable metals under mild conditions. Multiple characterization techniques confirmed that mechanochemical activation of sulfur induces structural distortion and partial amorphization of sulfide residue, generating defect-rich surfaces and a locally sulfur-enriched environment. During leaching, surface-associated sulfur species undergo in situ oxidation to generate acids, enabling autocatalytic enhancement. Under optimal conditions—12.5% sulfur additive, 1-hour ball milling, 130 °C leaching temperature, 0.5 MPa O₂, an L/S ratio of 8, and 2.5 hours of leaching—selective leaching rates of valuable metals exceeded 99%. Leaching kinetics showed a two-stage profile with low apparent activation energies for metals. Comprehensive TEA and LCA suggest that the technology effectively alleviates the inherent kinetic and thermodynamic limitations of leaching inert, sulfur-deficient sulfide minerals, without consuming acid or alkali and generating secondary pollution. It offers a novel, green, and practical pathway for the recovery of nickel–cobalt secondary resources, improves the energy efficiency, and promotes the circular economy of key metals.