A Study of Cementite Formation in the Reduction of Hematite by CO–CO 2 Gas Mixture Using High Temperature XRD Yury Kapelyushin, Yasushi Sasaki, Jianqiang Zhang and Oleg Ostrovski Abstract Formation of cementite in the reduction of hematite by CO–CO 2 gas was studied in situ using high temperature XRD (HT XRD) analysis. Reduction of hematite was examined in the temperature range 873–1173 K by CO–CO 2 gas mixture with high carbon activity. When carbon activity in the system was 1.5, cementite was formed only at 1023 K; it was not observed in experiments at 973, 1073 and 1123 K. Formation of cementite was observed at 923–1073 K when carbon activity increased to 3–5; and at 873 K when carbon activity was 10. Formation of cementite at 973–1073 K proceeded through metallic iron; however, in the reduction of hematite at 873 and 923 K, iron was not observed; cementite apparently was formed directly from wüstite. XRD spectra were used to estimate concentration of carbon in austenite in the process of cementite fromation. Keywords Cementite ⋅ Iron oxide ⋅ Gaseous reduction ⋅ High-Temperature XRD Introduction Cementite is a highly valuable charge material for the electric arc furnace (EAF) steelmaking. It was produced by Nucor in Trinidad in 1990s, although the full capacity was not reached, and operation lasted for only four years [1]. In that process, the reducing gas was made from natural and hydrogen. Natural gas is also used directly (unreformed) in HYL/Energiron processes, in which produced DRI can contain a significant fraction of cementite (1.4–4.0 wt% [2]). Cementite (iron carbide Fe 3 C) is formed in the reduction of iron oxides or by cementation of iron in the gas atmosphere (CO–CO 2 –H 2 or CH 4 –H 2 ) with high Y. Kapelyushin ⋅ Y. Sasaki ⋅ J. Zhang ⋅ O. Ostrovski ( ✉ ) The University of New South Wales, Kensington, Australia e-mail: o.ostrovski@unsw.edu.au © The Minerals, Metals & Materials Society 2018 B. Davis et al. (eds.), Extraction 2018, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-319-95022-8_54 683