Enhancing the Selective Reduction of Nickel to Prepare FeNi50 Alloy from Saprolite-Type Laterite by CO-CO₂ Gas Pretreatment

Owing to the superior reduction kinetics of limonite and goethite relative to silicates, coupled with the poor beneficiation performance of saprolite-type laterite, the direct carbothermal reduction of saprolite-type laterite exhibits limited nickel selectivity. This study leverages the selective oxidation effect of CO-CO2 atmosphere on metallic iron and its suppression of Fe2+ reduction to promote iron migration from oxides into the silicate phase, achieving homogenization and thereby negating its kinetic advantage in reduction. Parameter optimization experiments revealed that treating pre-reduced minerals with a 30 vol% CO atmosphere at 1200 °C for 20 minutes achieves complete iron homogenization within the silicate phase. Compared with the nickel-iron alloy (containing less than 10 wt% Ni) obtained via RKEF process, the combination of pre-reduction, CO-CO2 treatment, and melting reduction process yielded nickel-iron alloys with nickel contents of 52.1 wt% (FeNi50 alloy) and 64.2 wt% at carbon consumptions of 4.0 wt% and 3.83 wt%, respectively, accompanied by nickel recovery rates of 95.5% and 91.2%. Furthermore, the enrichment of Fe2+ in the slag significantly reduces its melting point to approximately 1450 °C, enabling complete slag-metal separation after smelting at 1550 °C for 10 minutes.