Oxidative Leaching of Unconventional Nickel Resources Using a Regenerable Cerium Redox System

Increasing demand for high-purity class 1 nickel is driving interest in unconventional nickel resources, including high-magnesium, low-grade sulfide concentrates and awaruite-bearing ultramafic materials. Here, we evaluate cerium(IV)-mediated oxidative leaching as a regenerable hydrometallurgical strategy for extracting nickel from these resources. High-magnesium sulfide concentrates, beneficiated sulfide concentrates, and awaruite-bearing feedstocks were leached using electrochemically recycled cerium(IV) nitrate or sulfate. The extraction kinetics were paired with XRD (X-ray diffraction) and SEM (scanning electron microscopy) /EDS (energy-dispersive X-ray spectroscopy) characterization to identify the mineralogical controls on nickel recovery and oxidant consumption. Leaching of acid-pretreated high-magnesium SMSU (semi-massive sulfide unit) concentrate showed rapid kinetics, with ∼84% nickel extracted within an hour. A second high-magnesium feedstock with a similar nickel grade exhibited slower kinetics and substantially higher oxidant consumption, which was attributed to competing pyrite oxidation during the leaching. Beneficiation significantly reduced oxidant demand, implicating pyrite rather than magnesium silicate gangue as the dominant parasitic oxidant sink. Further investigation of awaruite (Ni3Fe) feedstocks revealed rapid and selective leaching behavior: both cerium(IV) nitrate and sulfate extracted ∼98% nickel within 20 min. Awaruite feedstocks also consumed substantially less oxidant, consistent with direct alloy oxidation and minimal competing reactions. These results show that recyclable cerium redox chemistry can enable nickel recovery from smelter-incompatible sulfide concentrates and emerging awaruite resources.