The Performance of Pyrolyzed Palm Oil Bunch for Limonitic Laterite Ore Reduction: Total Iron and Nickel Recovery and Phase Transformation

This study evaluates the performance of pyrolyzed oil palm empty fruit bunch (OPEFB)-derived char as a sustainable reductant for the carbothermic reduction of limonitic laterite ore, followed by magnetic separation to enrich iron (Fe) and nickel (Ni). OPEFB was pyrolyzed at 400°C and 600°C and compared with conventional coal, including selected coal–OPEFB blends, to assess potential interaction effects. Reduction experiments were conducted at 1150°C for 60 min under sub-stoichiometric conditions. The results showed that OPEFB-derived char significantly enhanced metal enrichment, increasing Fe content from 46.92 wt.% to 66.16–78.09 wt.% and Ni content from 0.77 wt.% to 0.96–1.26 wt.%, with recovery rates of 67.07–79.52% for Fe and 67.85–75.95% for Ni. Blended systems further improved Ni recovery up to 87.86%, indicating potential synergistic effects between coal and biomass-derived reductants. Phase analysis (XRD) confirmed the transformation of iron and nickel oxides into metallic and intermediate phases, including wüstite (FeO), magnetite (Fe₃O₄), and Fe–Ni alloy (Fe_0.7Ni_0.3). SEM-EDX observations revealed larger and more densely distributed Fe–Ni alloy particles in OPEFB-containing samples compared to coal-based systems. TG-DSC analysis indicated that the higher volatile content of OPEFB-derived char promotes enhanced devolatilization and gas-phase reactions, which are likely associated with improved reduction behavior. These findings demonstrate that OPEFB-derived char is a promising alternative reductant for laterite processing and highlight the critical role of biomass-derived volatiles in influencing reduction performance.