Reduction of iron oxide compacts with simulated blast furnace top and shaft gases to mitigate CO 2 emissions

The mitigation of CO₂ emissions has become a global priority in the iron and steel industry. One promising solution to decrease CO₂ emissions is recycling of the blast furnace top gas to be reused in the reduction of iron oxide. In this study, iron oxide compacts were reduced isothermally with simulated conventional blast furnace top gas (BFTG: 20%CO, 20%CO₂, 5%H₂, 55%N₂) at 700–900°C using a thermogravimetric technique. The reduction reached 30–34% depending on the applied temperature. The compacts were reduced completely to wüstite (Fe_0·925O or Fe_0·971O) with a few grains of metallic iron, which appeared only at 900°C. To investigate the reduction behaviour at the later stages, the compacts reduced with BFTG at 900°C were followed by isothermal reduction with simulated blast furnace shaft gas (BFSG: 30%CO, 5%CO₂, 10%H₂, 55%N₂) at 950–1100°C. The total reduction extents were increased to 66–90% at 950–1100°C respectively. The remaining unreduced wüstite (Fe_0·974O) has a higher Fe/O ratio compared with that formed by reduction with BFTG. At the initial stages of reduction, the rate controlling mechanism was interfacial chemical reaction, while at the later stages, solid state diffusion was the rate controlling mechanism. Reflected light microscope, scanning electron microscope, X-ray diffraction and Poresizer techniques are used to estimate the reduction kinetic and mechanisms.