Overcoming acid dependency: A near-neutral pH bioleaching approach for polymetallic sulfides

• A near-neutral pH bioleaching approach has been proposed. • A marine microbial culture was used for the first time in mineral bioleaching. • High selectivity for the ligands with NTA much better than glycine was revealed. • The effects of Co doping and Fe elution on mineral dissolution were revealed. • Bacterially enhanced galvanic selective dissolution of pentlandite was proposed. Bioleaching represents a significant technological approach for the processing of low-grade resources. However, conventional acid bioleaching is not a viable option for the processing of alkaline materials, such as polymetallic sulfide hosted in mafic/ultramafic rocks (PSHMR), owing to its high acid consumption and elevated levels of dissolved impurities. In this study, a near-neutral pH (∼7.7) bioleaching approach is presented that has been shown to extract 73.5% Ni, 67.7% Co, and only 3.9% Mg from a PSHMR. This approach integrates the bacterial oxidation of reduced sulfur facilitated by a marine microbial culture (MCCC 1A13021) and the selective coordination extraction of Ni and Co using a nitrilotriacetic acid (NTA) ligand, trisodium nitrilotriacetate (Na 3 NTA). The study proposes a bacterially enhanced galvanic selective dissolution of Co-bearing pentlandite in the presence of chalcopyrite, pyrrhotite, and magnetite. The NTA ligand exhibited robust biological affinity, effective pH buffering capacity, and antibiodegradability, laying the foundation for recycling ligands in subsequent column and heap leaching practices. The near-neutral bioleaching method helps circumvent a series of drawbacks associated with acid bioleaching and holds broad prospects for application in extracting metals from alkaline materials and the biooxidation of gold-bearing sulfides, thereby promoting the sustainable development of the bioleaching method.