Currently, steelmaking industry is still one of the major CO2 emission sectors in Europe, which emits 4 % of the EU’s total CO2 emissions [1]. The two dominant steelmaking process are the blast furnace–basic oxygen furnace (BF–BOF) route and the scrap-based electric arc furnace (EAF) route [2,3]. In terms of CO2 emission, the BF–BOF route emits 1.6-2.2 tons CO2 per ton of crude steel, which is nearly twice amount CO2 emission than that of EAF route (0.6-1.1 tons CO2 per ton of crude steel) [4–6]. To achieve the goal of CO2 neutral within the process, the shift from BF-BOF to EAF is a trend for future steelmaking [3]. Due to the limit to access to high quality scrap, it can be partly replaced by the direct reduced iron (DRI). The ongoing development of hydrogen based direct reduced iron (HyDRI) - EAF route has high potential for reducing CO2 emission. When EAF is operated with pure HyDRI, CO2 emission can be reduced to 25-53 kg per ton of crude steel [7,8].

Many commercial processes use shaft furnaces or fluidized bed reactors as iron ore reduction units to produce HyDRI. Fluidized beds usually show better reduction efficiency because of faster mass and heat transfer. However, when the de-fluidization phenomenon occurs, i.e., the iron ore fines cannot be fluidized by the gas flow, the reduction efficiency will drop dramatically, and process control of the system will become impossible. Especially, it is difficult to operate magnetite-based iron ores in a fluidized bed. Pre-treatment of magnetite-based iron fines are required to prevent the de-fluidization. Hydrogen reduction of iron oxide is an endothermic reaction, which requires external heat input into the system, such as preheat of the iron ore. When magnetite iron ore is used, it becomes oxidized in preheat process. The oxidation of magnetite may have an influence on its subsequent reduction. The current work aims to test different parameters in pre-treatment unit to improve the fluidization and reduction behaviours of magnetite-based iron ore fines. Furthermore, an optimum operation condition is confirmed