Study on pore structure of iron phase in magnetite pellets reduced by pure hydrogen based on nitrogen adsorption method

In this study, the isothermal reduction behavior of magnetite pellets in pure hydrogen at 1373 K was investigated, and the pore evolution mechanism of the iron phase had been studied using scanning electron microscopy and nitrogen adsorption. The results showed that the reduction process of the pellets could be divided into three stages: rapid reaction, transition stage, and stagnation stage. The pore structure of the iron phase in the reduction process was evolving dynamically, and the metallic iron in the early reduction stage was a honeycomb structure with a concentration of small-size cross-linked pores, while in the later reduction stage, the metallic iron was mostly dense, and the internal pores became larger and more labyrinthine structure. Under different reduction time, the average pore size in the iron phase was 4.89–26.17 nm, the pores included micropores, small pores and mesopores, in which 5–10 nm micropores were dominant. These pores had good fractal characteristics, and the fractal dimension value was 2.478–2.863. Furthermore, the mechanism of pore formation in the iron phase was driven by the dynamics of H₂ dissociation, diffusion, and Fe/FeO interfacial reactions.