Pretreatment-free direct flotation of Co-Ni from reagent-laden sulfide concentrate: An industrial demonstration

The efficient recovery of strategic cobalt (Co) and nickel (Ni) from complex secondary resources is crucial for resource security. This study addresses a key bottleneck hindering short-process all-flotation routes: the difficulty in direct separation of reagent-coated sulfur-cobalt bulk concentrate derived from pre-concentrated vanadium titanomagnetite tailings. A synergistic reagent system featuring a calcium-based composite modifier (CCM) and a mercapto-based depressant (3-MP) was developed, enabling flotation separation of industrial reagent-laden sulfide feed without any pretreatment. In laboratory closed-circuit tests, a Co-Ni concentrate assaying 2.16% Co and 4.95% Ni was produced from 0.35% Co feed, with 80.82% Co and 79.65% Ni recoveries and a Co/S selectivity coefficient of 5.9, which compares favorably with traditional pretreatment-dependent processes. The process was scaled up to a 30,000 tonne per annum industrial production line. Stable operation yielded a Co-Ni concentrate (1.82% Co, 4.35% Ni), salable sulfur concentrate with sulfur content of no less than 30%, and confirmed simultaneous copper recovery. This work offers a practically and industrially tested framework for short-process clean recovery of critical metals from sulfide ores.