The steel industry today is a significant contributor to global CO2 emissions, and the transition toward fossil-free steelmaking has accelerated the shift to production in electric arc furnaces (EAF). Direct reduced iron (DRI) is a key technology in this development, traditionally relying on natural gas as the reducing agent, but now exploring hydrogen as a sustainable alternative to produce hydrogen-based direct reduced iron (H-DRI). The mining company Kaunis Iron, located in Kaunisvaara, Sweden, is currently exploring a new magnetite deposit containing elevated levels of magnesium bound within the magnetite lattice. Prior to this study, the ore had been successfully reduced with hydrogen in Metso’s Circored fluidized bed process in Frankfurt, Germany.

This study investigates the unexplored melting and slag-forming behavior of the magnesium-containing Kaunis Iron H-DRI under simulated EAF conditions. The main objective was to provide initial indications of whether the MgO in H-DRI could reduce or replace externally added magnesia from conventional slag formers. To examine this, designed melting tests were performed at Metso’s facility in Pori, Finland. The experiments were conducted at 1660°C under an argon atmosphere with holding times of 10 and 120 minutes. The tests were carried out in MgO crucibles without adding external magnesium sources, to determine whether the MgO in the slag originated from the H-DRI or from crucible dissolution. The experimental work was complemented by thermodynamic calculations in FactSage and material characterization using SEM/EDS, XRD, and DSC analyses.

Analysis of the H-DRI showed that it primarily consisted of magnesiowüstite as the dominant Mg-bearing phase, together with minor Fe-bearing forsterite. Oxide melting was initiated at relatively low temperatures around 1380°C according to FactSage calculations and approximately 1490°C for the average magnesiowüstite composition based on SEM/EDS analysis. DSC results also indicated the onset of melting near 1464°C, all occurring below the melting point of metallic iron at 1538°C. The resulting slags from the designed melting tests closely matched the target composition of 40wt% CaO, 30wt% FeO, 20wt% SiO2, and 10wt% MgO. A thin magnesiowüstite layer formed at the slag–crucible interface, measuring about 88 µm after 10 minutes and 110 µm after 120 minutes of holding time, indicating negligible crucible interaction.

The results show that MgO in the slag originated mainly from the H-DRI, actively contributing to slag chemistry and indicating that reducing the need for external magnesia additions in EAF steelmaking could be a possibility. Nevertheless, further research is needed to test the repeatability of these findings and to investigate them under more advanced conditions.