Abstract
Steel production in the electric arc furnace (EAF) is continually growing as more steel is recycled, generating large amounts of iron-rich by-products, such as EAF black slag (≥45 wt.% FeO) and rolling mill scale (≥75 wt.% Fe). These by-products represent a substantial secondary iron resource, but much of their iron remains chemically bound to oxide phases, where impurities may hinder reduction kinetics and, thereby, limit iron recovery. Hydrogen offers a promising alternative to carbothermic methods for the development of sustainable valorisation routes of such iron-bearing steelmaking by-products. This study approaches key scientific challenges related to the use of hydrogen as a reductant for two relevant secondary steelmaking resources: rolling mill scale and EAF slag. Hydrogen-based reduction experiments were conducted on industrial mill scale pellets to evaluate impurity effects on metallic iron formation. Complementary, thermodynamic and slag foaming simulations were performed for EAF slag at 1600 °C to estimate the theoretical iron recovery and the associated slag foaming capacity during the hydrogen-bubbling reduction. By integrating these experimental and modelling approaches, this work expands hydrogen-based reduction to complex oxide systems and provides a framework for the development of low-carbon, circular strategies for iron recovery in future steelmaking.