New approach to reduce carbon emissions by hydrogen reduction of boron-bearing iron concentrate in a fluidized bed: Reduction kinetics and microstructure analysis

Iron ore reduction using hydrogen instead of coal is a promising technology for minimizing CO2 emissions in the metallurgical industry. In this study, the hydrogen reduction mechanism and kinetics of boron-bearing iron concentrate were investigated in a fluidized bed at 650 similar to 850 degrees C, and the reduction data were quantified with an online gas composition analysis technique. The kinetics parameters were calculated using the model-free method and conventional kinetics model, and the mineral phase composition and micromorphology characteristics of reduced products were analyzed. The results showed that the reduction process of boron-bearing iron concentrate in a fluidized bed can be divided into two periods, with the earlier period was controlled by the spherical shrinking model and the later period was controlled by the three-dimensional diffusion model, and the apparent activation energy was significantly increased from 65.22 kJ/mol to 96.11 kJ/mol. Firstly, the magnetite was rapidly reduced to wustite and dense metallic iron. With an increase in the thickness of the metallic iron layer, the diffusion of oxygen through the dense iron became the rate-limiting step of the reaction, and the defects within the iron layer played a pivotal role in the following mass transfer process. However, the reduction of ludwigite did not suffer from this restriction since the dense product layer was absent.