External moisture enhanced synergistic conversion of biomass and iron sand for the green production of metallic iron

In this study, a novel approach combining chemical looping gasification (CLG) and direct reduced iron (DRI) was proposed for an efficient, sustainable, and green production of metallic iron by enhancing the synergistic conversion between biomass and iron sands via external moisture. In the process, the external moisture acts as a catalyst for pre-gasification of biomass at the early stage while iron sand, as an oxygen carrier (OC) and catalyst, contributes to the later biomass gasification, where biomass is used as a reducing agent for iron ore metallization. The effect of moisture on biomass gasification and roasting effectiveness was investigated, at a reduction temperature of 1080 °C, 10% H2O, and 80 min of roasting time. The total syngas yield was 84.13% and the reduction product with a metallization rate of 97.53% was obtained. The mechanism of synergistic conversion between biomass, external moisture, and iron sand was described. The iron ore and moisture in the initial roasting stage reduced the tar yield, significantly retarded the escape of hydrocarbons, and prolonged the high-pressure maintenance time. Thereafter, the biomass tar and biomass carbon were gasified under the action of oxygen elements from external moisture and iron ore, eventually generating CO and H2 with the final residual carbon being 9.73% comparing to the initial total C element. The reducing gas generated from biomass was used to reduce iron ore, ensuring a high metallization of iron ore and achieving efficient synergistic conversion of biomass and iron ore. Moisture and lattice oxygen of iron ore play significant roles in the gasification of biomass at the early stage. The formed metallic iron and moisture further promoted the gasification of biomass C in the subsequent catalysis. This mutually reinforcing and transformative approach shows great potential in promoting biomass gasification efficiency and reducing carbon emissions from DRI processes.