Iron-Iron Oxide Composites via Hydrogen Reduction of Mill Scale Followed by Spark Plasma Sintering

Abstract

The shift toward sustainable and low-carbon ironmaking has driven the need for innovative approaches. Key strategies include establishing a circular economy by recycling iron-rich waste (by-products) from steel production and using hydrogen (H₂) as a clean reducing agent to minimize the CO₂ emissions. Mill scale from hot rolling mills during steelmaking is an attractive industrial waste due to its high iron content (about 72 wt.%) in the form of wustite (FeO), hematite (Fe₂O₃), and magnetite (Fe₃O₄). This study employs a one-step thermo-chemical treatment to partially reduce the mill scale to synthesize iron-iron oxide composites. The direct reduction of mill scale is carried out at 500℃ and 650°C for 90 min in flowing H₂ gas. Such partially reduced mill scale powder was then consolidated by spark plasma sintering. Detailed characterizations were carried out using X-ray diffraction, optical microscopy, and scanning electron microscopy of treated and untreated mill scale at various stages of the process, before and after compaction. A discussion of environmentally friendly hydrogen reduction as a process for converting mill scale into useful powder metallurgy steel products is presented.