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 the metallic iron of pre-reduced minerals, as well as its suppression of Fe²⁺ reduction, to promote iron migration from oxides to 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 min achieves complete iron homogenization within the silicate phase. Compared with the nickel–iron alloy (containing less than 10 wt% Ni) obtained via the RKEF process, the combination of pre-reduction, CO-CO₂ treatment, and the 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 min.