Swelling Behavior of Iron Ore Pellets during Reduction in H₂ and N₂/H₂ Atmospheres at Different Temperatures

Abstract

The need to develop green steelmaking techniques has led to the replacement of reducing agents such as CO with H2. H2 and N2/H2 mixtures can be used for the carbothermal reduction of iron ore. Herein, the reduction swelling index (RSI) of iron ore pellets in a forming gas (N2/H2) atmosphere at temperatures of 700–1000 °C is investigated and it is compared with that in pure H2. It is showed in the experimental results that the RSI increases with increasing temperature for both the H2 and N2/H2 atmospheres. The maximum swelling is reached approximately 5 min into the H2 reduction process, while in the N2/H2 atmosphere, it is reached after 25–45 min of reduction, depending on the temperature. When the reduction temperature exceeds 900 °C, the RSI is greater than 20%. Scanning electron microscopy/energy‐dispersive X‐ray spectroscopy is performed to detect the changes in the microstructure and chemical composition of the samples. The nonreduced areas in the reduced pellets during the N2/H2 reduction process are analyzed using light optical microscopy.

An Overview Analysis of Current Research Status in Iron Oxides Reduction by Hydrogen

“…The Reduction Swelling Index (RSI) quantifies the increase in pellet volume during reduction and is known to rise with increasing temperature [58,105,106]. Scharm et al found that the RSI is significantly higher in an H 2 atmosphere compared to a CO atmosphere, peaking during the first stage of reduction (Figure 13) [58].…”

“…Zhao et al observed that the RSI of pellets decreases with increasing H 2 content; they also noted that temperature has a more significant impact on swelling than the composition of the reducing atmosphere [105]. Kovtun et al found that the chemical composition and porosity of pellets significantly affect the RSI; specifically, pellets with lower gangue (CaO and SiO 2 ) content exhibited higher RSI at the same temperature [106]. Conversely, Sharma et al reported that an increase in gangue content leads to a decrease in RSI [108].…”