In addition to electric steel mills, which produce steel mainly by melting steel scrap, hydrogen- or natural gas-based direct reduction processes are increasingly being used instead of the classic blast furnace route.

Here, iron ore is first used to produce sponge iron (Direct Reduced Iron (DRI) or Hot Briquetted Iron (HBI)), which is then melted into crude steel in the subsequently placed electric arc furnace or alternative melting units (such as huge induction furnaces) together with scrap or other iron carriers.

Hydrogen- and / or natural gas-based direct reduction processes plus subsequent electric arc furnaces are much more sustainable than the conventional blast furnace route: compared to this classic route, CO2 emissions are significantly reduced with H-DRI.

Using average values in the technology comparison show that the scrap-based electric arc furnace (EAF) steel production route saves about 75 % of the CO2 produced compared to the conventional blast furnace route (BF/BOF). The the direct reduction (DRI) route (natural gas-based) saves about 50 to 60% per cent compared to the conventional blast furnace route (BF/BOF).

The use of hydrogen in the direct reduction process increases the savings effect even further, even down to a few percent emissions.

It must be considered however that the focus in the strategy and technology change to CO2-emission-avoiding CDA processes (Carbon-Direct-Avoidance) must be placed on the highest product qualities and grades, maximum flexibility in the input materials as well as continuous and energy-efficient process management in order to economically design recycling processes to minimise resource consumption.

With its positive environmentally relevant properties, steel scrap makes an important contribution to green steel production - and its importance in the steel production process will continue to grow. Technological conversions will increase the demand for scrap in the future, which will also produce steel of the highest quality when mixed with other iron carriers, such as from direct reduction processes.

Future green steel making can also take on the role of a holistic recycling system in which other materials (e.g. non-ferrous carriers) are separated and discharged in addition to steel. Corresponding recycling plants already exist. The first considerations by steel mills to undertake the task of processing scrap into high-quality scrap in their own plants are already being made or are in the planning stage.

Unwanted chemical contamination and lack of scrap availability can become a problem in future green steel making. We might encounter the problem a decreasing scrap quality in terms of density, Fe content and the lack of availability of high-quality scrap. In addition, steel production suffers from the increasing proportion of undesirable by-elements or impurities, such as copper, chromium, nickel or molybdenum, which makes the steel production process, and secondary metallurgical processes in particular, costly or the desired qualities can only be produced by dilution with DRI/HBI. 

The demands of the steel mills on the recycling industry in terms of quantity, quality and purity of the delivered scrap will increase in the future. The scrap industry will have to continue to invest in its scrap processing facilities in order to be able to provide the scrap qualities demanded by the steel industry. In the long term, scrap availability will cover about 50 per cent of the steel producers.

The increasing reliance on steel scrap as a secondary raw material in steel production is driven by both economic and environmental imperatives, particularly the need to reduce carbon emissions associated with primary steelmaking. However, the recycling of steel scrap introduces challenges related to contamination by residual elements, among which zinc is particularly significant due to its prevalence in coated steel products and its profound impact on metallurgical processes and material properties.  

Zinc contamination in steel scrap primarily originates from galvanized steel, which is widely used in automotive, construction, and appliance industries for its corrosion resistance. During the recycling process, zinc volatilizes in the high-temperature environment of electric arc furnaces (EAFs), leading to its accumulation in dust and slag. While modern filtration systems capture a substantial fraction of this zinc, residual amounts may dissolve into the molten steel or form deleterious intermetallic phases. The presence of zinc in steel melts can influence the thermodynamics of slag formation, alter the solubility of other tramp elements such as copper and tin, and contribute to the formation of non-metallic inclusions, which degrade mechanical properties.  

At the microstructural level, zinc contamination exacerbates the phenomenon of liquid metal embrittlement (LME), particularly in high-strength steels subjected to thermomechanical processing. Zinc, when present at grain boundaries or interfaces, lowers the cohesive energy and promotes crack initiation under stress, leading to premature failure. Furthermore, zinc interacts with other residual elements, such as lead and antimony, to form low-melting-point phases that segregate during solidification, impairing hot ductility and weldability.  

From a sustainability perspective, zinc contamination complicates the circular economy paradigm for steel. While zinc recovery from EAF dust is technically feasible through hydrometallurgical or pyrometallurgical routes, the economic viability of these processes depends on zinc market prices and regulatory frameworks. Moreover, the progressive accumulation of zinc in recycled steel loops necessitates careful scrap sorting and dilution strategies to maintain product quality. Advanced sensor-based sorting technologies and machine learning algorithms are being developed to improve the separation of zinc-coated scrap, but their widespread adoption remains limited by cost and scalability.  

In conclusion, zinc contamination in steel scrap represents a critical challenge for the metallurgical industry, affecting both process efficiency and material performance. Mitigation strategies must integrate improved scrap classification, optimized furnace practices, and innovative purification techniques to ensure the sustainable recycling of steel without compromising its structural integrity. Future research should focus on the fundamental interactions between zinc and other tramp elements, as well as the development of alloy designs tolerant to increasing impurity levels in recycled steel feedstocks.

As outlined above the recycling of steel scrap (the so called secondary synthesis route) is an essential cornerstone of sustainable metallurgy, significantly reducing energy consumption and CO₂ emissions compared to primary steel production. However, the accumulation of residual copper in the steel scrap stream presents substantial challenges to both process efficiency and final product quality. Copper contamination primarily originates from electrical wiring, motors, and alloyed components mixed into the scrap supply, with typical concentrations ranging from 0.1 to 0.5 wt.% in general scrap and exceeding 1 wt.% in poorly sorted feedstock.

Copper exhibits limited solubility in ferrite, with a maximum equilibrium solubility of approximately 0.02 wt.% at room temperature. During solidification, excess copper segregates to grain boundaries and interdendritic regions, where it forms low-melting-point phases in combination with other residual elements such as tin and antimony. This segregation behavior becomes particularly problematic during hot working, as copper-rich liquid films form at grain boundaries and below the oxide / scale surfaces of the hot steels (as the Cu is rejected from teh oxides, and thus enriches below these oxides) at temperatures as low as 1085°C (the melting point of pure copper), leading to hot shortness and surface cracking. The phenomenon is exacerbated in high-strength low-alloy (HSLA) steels, where copper concentrations above 0.3 wt.% can reduce hot ductility by more than 50%, as measured by reduction-in-area values in hot tensile tests.

In addition to hot-working defects, copper contamination adversely affects the mechanical properties of finished steel products. Experimental studies demonstrate that copper contents exceeding 0.2 wt.% can reduce impact toughness by up to 30% due to the precipitation of ε-Cu particles (5–20 nm in diameter) during aging. These precipitates, while contributing to precipitation hardening, simultaneously embrittle the material by promoting cleavage fracture. Furthermore, copper increases susceptibility to corrosion, particularly in atmospheric environments, where it accelerates the formation of non-protective rust layers. Electrochemical measurements reveal that steels containing 0.4 wt.% Cu exhibit corrosion rates up to 20% higher than copper-free counterparts under identical exposure conditions.

From a process metallurgy perspective, copper is particularly troublesome because it cannot be removed by conventional oxidative refining in electric arc furnaces (EAFs). Unlike elements such as carbon or silicon, which partition into the slag or gas phase during oxidation, copper remains entirely in the molten steel. This leads to a progressive accumulation in recycled steel loops, with industrial data indicating an annual increase in average copper content of 0.01–0.02 wt.% in the global scrap pool. Advanced mitigation strategies, including scrap pre-sorting via laser-induced breakdown spectroscopy (LIBS) and X-ray transmission sorting, can reduce copper levels to below 0.1 wt.%, but these methods entail significant operational costs.

The thermodynamic and kinetic limitations of copper removal have spurred research into alternative approaches, such as sulfide-based slag treatments and solvent extraction from molten steel. However, these methods remain largely experimental, with industrial implementation hindered by efficiency and scalability challenges. Consequently, the most viable near-term solution lies in improved scrap classification and the development of copper-tolerant steel grades, where microalloying with nickel (at Ni/Cu ratios ≥1:1) mitigates hot shortness by stabilizing austenite at high temperatures.

In essence, copper contamination in steel scrap represents a critical metallurgical issue with cascading effects on processability, mechanical performance, and corrosion resistance. Quantitative analysis confirms that even marginal copper concentrations impair material properties, while the irreversible nature of its accumulation demands systemic improvements in scrap management. Future advancements must integrate smarter sorting technologies, optimized alloy design, and novel refining techniques to ensure the continued viability of steel recycling in a circular economy framework.