Selective Cobalt Extraction from Low-Grade Cobalt-Bearing Pyrite via Oxygen Pressure Acid Leaching

Cobalt occupies an irreplaceable strategic position in renewable energy and high-end advanced industries. As high-grade mineral resources gradually deplete, associated sulfide minerals have attracted increasing attention as alternative sources of cobalt. This study investigated a selective extraction of cobalt from low-grade cobalt-bearing pyrite using oxygen-pressure acid leaching. The Gibbs free energy (ΔG) of key chemical reactions in the leaching system was calculated to verify the thermodynamic feasibility of the process. The effects of critical parameters, including oxygen pressure, initial acidity, stirring speed, leaching time, and temperature, on cobalt leaching efficiency and phase transformation characteristics were systematically investigated. Under optimal conditions of oxygen pressure 1.5 MPa, H2SO4 initial acidity 7.36 g·L−1 (0.82 mol/L), stirring speed 300 rpm, leaching duration 120 min, and temperature 230 °C, the cobalt leaching rate reached 98.2%, whereas the leaching rates of iron and aluminum were only 19.79% and 28.11%, respectively. Combined with SEM-EDS, XRD, and XPS characterization results, oxygen pressure acid leaching effectively destroyed the lattice structure of cobalt-bearing pyrite and liberates lattice-hosted cobalt, thereby facilitating efficient cobalt leaching. At high-temperature and oxygen pressure conditions, Fe3+ underwent hydrolysis and precipitated as hematite (Fe2O3) or hydronium jarosite (H3O)Fe3(SO4)2(OH)6, enabling the selective extraction of cobalt. Aluminum in cobalt-bearing pyrite primarily occurred as the stable boehmite (AlOOH) phase, exhibiting excellent acid resistance and low dissolution during leaching. This study broadens the utilization pathway of low-grade cobalt resources and provides valuable insights and a scientific theoretical basis for the efficient treatment of cobalt-containing sulfide concentrates and tailings.