Abstract
The depletion of high-grade sulfide deposits has shifted attention to abundant but underutilized ultramafic ores; however, their high MgO content hinders flotation, increases leaching reagent consumption, and elevates smelting liquidus temperatures. This study investigates a low-temperature upgrading approach in which ultramafic concentrates are blended with Fe powder and heated to 920 °C. During treatment, Fe reacts with sulfur-bearing minerals to form nonmagnetic FeS, thereby mitigating SO2 emissions, while excess Fe alloys with Ni to produce magnetic FeNi, enabling magnetic separation. Under an Fe-to-concentrate ratio of 0.25 and two-stage treatment (920-750 °C), FeNi particles with a Dv80 of ~92 µm were obtained. A 10 vol.% H2 atmosphere promoted FeNi growth by lowering Fe oxidation potential. To reduce Fe powder consumption, recycled FeNi middlings were introduced as a substitute Fe source. The middlings also acted as pre-existing metallic nuclei, thereby enhancing FeNi particle growth during treatment. Partial Fe substitution (50 wt.%) increased Dv80 to 136 µm, whereas full substitution (100 wt.%) yielded 112 µm due to excessive nucleation density. Ni extraction decreased from 92 wt.% (no Fe substitution) to 88 wt.% (full substitution) because pure Fe powder is more chemically active. Overall, controlled seeding offers a resource-efficient route for upgrading ultramafic concentrates.