Insights into direct reduction iron using bamboo biomass as a green and renewable reducer: Reduction behavior study and kinetics analysis

Biochar is a renewable, carbon-neutral energy source that can replace traditional fossil fuels for iron and steel production, so it is of great significance to reduce carbon emissions and reduce pollution. In this paper, the reaction characteristics and kinetics between biomass (bamboo powder) pyrolysis gas, biochar, and iron ore powder are studied by a thermogravimetric analyzer (TG). Comparing the samples with four different C/O ratios (C/O = 0.375, 0.5, 1, 3), it is found that the sample with C/O = 1 can completely reduce hematite. The mass loss process is divided into the following four stages: de-crystal water, hematite to magnetite, magnetite to wustite, and wustite to metallic iron. Among them, the latter three stages are following the kinetic model of random nucleation (n = 1, 2) and three-dimensional diffusion, and the activation energy of the three stages increases and then decreases. Through scanning electron microscopy (SEM), the surface of hematite particles changed from relatively flat to porous and finally the reduced metal iron aggregated, and connected into large pieces. By using online Thermogravimetry-Fourier Transform Infrared Reflection (TG-FTIR), when the reduction temperature is lower than 700 °C, biochar plays a leading role. On the contrary, the CO produced by biochar gasification plays a leading role.