Sustainable Steel from Scrap: Cu Removal from Steel Melts

Cu removal from scrap-based steel melts is one of the big chellenges of sustainable steel production. 

Steel is the most widely recycled metallic material, with global scrap recycling volumes of approximately 460 Mt per year, representing a major opportunity for reducing CO₂ emissions in steelmaking.

Scrap-based electric arc furnace (EAF) production can cut greenhouse gas emissions by up to 85 % compared to the blast furnace–basic oxygen furnace route.

However, growing use of mixed scrap streams introduces impurities that are not fully removable by conventional metallurgical processes.

Copper (Cu) is a critical case in scrap-based steel melts: it is increasingly present in scrap due to electrification trends, is highly soluble in molten iron, resists slag partitioning, and is more noble than Fe, making oxide-based removal difficult. Even at levels above ~0.1 wt %, Cu causes hot shortness during hot working, limiting processability and product integrity. Projections indicate that by 2050, Cu content in global scrap will exceed tolerable thresholds for most steel grades, constraining closed-loop recycling.

Experimental and thermodynamic investigations have shown that Cu evaporation from Fe–Cu–O melts is strongly dependent on the global oxygen concentration. A critical oxygen content of about 22 wt % was identified, at which the activity of Cu in the molten phase is maximised and its evaporation rate peaks. Above this value, oxygen stabilises oxide structures that bind Cu; below it, Cu dissolves preferentially in metallic Fe, reducing its vapor pressure.

Laboratory trials in an arc melting furnace were carried out on binary Fe–Cu alloys and ternary Fe–Cu–O mixtures under inert (Ar) and reducing (Ar–10 % H₂) plasma atmospheres. In binary alloys, Cu removal was minimal. In oxygen-containing melts, significant Cu evaporation occurred during the reduction interval when oxygen decreased from ~29 wt % to ~22 wt %. Up to ~90 % Cu removal was achieved at 1850 °C under hydrogen plasma, with Fe losses of only ~2 %. Thermodynamic modelling confirmed these trends, predicting ~75 % removal at 1850 °C, ~50 % at industrial tapping temperatures (1650–1700 °C) with negligible Fe losses, and up to ~90 % in hotter arc zones (~2000 °C) at the expense of higher Fe evaporation (~8 %).

Based on these findings, a process route is proposed in which Cu-contaminated scrap is co-charged with iron ore to adjust the melt oxygen content to the critical ~22 wt % range. An initial melting stage under inert plasma or even oxidising air is used to maximise Cu evaporation, enabling recovery from the off-gas. The melt is then reduced to metallic Fe using hydrogen plasma, carbon, or other reductants. This method actively removes Cu instead of merely diluting it with primary iron, and simultaneously produces high-purity iron for steelmaking while recovering Cu as a secondary resource.

Proof-of-concept tests using magnetite and Cu-containing scrap (1 % and 5 % Cu) achieved Cu removals of 60–85 % with minimal Fe losses under inert plasma. Modelling indicates that similar results are possible in oxidising atmospheres at critical oxygen levels, with 20–80 % Cu evaporation depending on temperature.

Integration into industrial practice could occur in hydrogen plasma reduction reactors, using scrap as an ignition facilitator and Cu source, or in modified EAFs designed for higher oxygen-content melts. Implementation would require solutions for mass transport to the plasma zone, refractory linings resistant to FeO-rich melts, control of gangue element removal, and capture of Cu from exhaust gases. Process scalability also depends on achieving sufficient melt circulation to expose the bulk to the high-temperature reaction interface.

This approach offers a potential pathway to delay Cu saturation in the global scrap cycle, extend the viability of high-recycled-content steel, and recover Cu for use in electrification technologies. It aligns with the transition to low-carbon primary steelmaking and could be incorporated into next-generation green steel production systems.