Structural Optimisation and Reactivity Evaluation of Ferro-Coke Produced using Australian Coals

With the integrated BF-BOF route accounting for 70% of global steel production, decarbonisation remains a critical priority. Ferro-coke has emerged as a strategy to reduce emissions of BF ironmaking and raw material costs. During carbonisation, iron oxides reduce to metallic iron, which catalyses gasification and lowers both the onset temperature and the thermal reserve zone temperature. This catalytic effect, combined with improved burden permeability, enhances carbon utilisation and significantly decreases the BF fuel rate.

This project evaluated the feasibility of manufacturing high-strength ferro-coke briquettes using Australian raw materials, specifically contrasting the performance of Direct Reduced Iron (DRI) against standard iron ore fines, and assessing the efficacy of High-Fluidity (HF) coal versus Coal Tar Pitch (CTP) as binding agents.

The investigation reveals a fundamental divergence in mechanical integrity governed by the oxidation state of the ferrous additive. Blends incorporating DRI demonstrated significant structural reinforcement and enhanced tensile strength, whereas the addition of iron ore resulted in severe strength degradation. This disparity is attributed to the rheological suppression caused by reducible iron oxides, which scavenge the transferable hydrogen necessary for stabilising the coal metaplast, leading to a weakly bonded matrix. Furthermore, CTP was identified as the superior binder, generating the necessary swelling to mechanically interlock the aggregate, unlike the HF coal, which failed to prevent structural discontinuity at high loadings.

Structurally, the superior performance of DRI-based ferro-coke was characterised by the formation of a robust, interconnected, and highly anisotropic carbon network that maintains beneficial porosity. Conversely, iron ore additions promoted densification and the formation of isotropic textures. Thermogravimetric analysis confirmed that the favourable microstructure of the DRI-CTP blends translates to superior gasification kinetics, characterised by a distinct bimodal reaction profile and a significantly lowered catalytic onset temperature.

This project identifies the formulation combining DRI with a CTP binder as the optimal pathway for producing ferro-coke that successfully balances the competing requirements of high mechanical strength and high physicochemical reactivity.