Biochar in Metallurgy: Turning Waste Carbon into Green Steel

The Fossil Problem in Steel

Steelmaking accounts for around 8% of global Carbon Dioxide emissions. The industry relies heavily on coal and coke both as fuels and as reducing agents that convert iron ore into metallic iron. These carbon-based inputs make the sector one of the hardest to decarbonise.

Replacing fossil carbon with renewable alternatives has long been a focus of research. Among the emerging candidates, biochar stands out for its renewable origin, chemical similarity to coke, and versatility across metallurgical applications.

Biochar: From Biomass to Metallurgical Carbon

It is to be noted that the key to success lies in tailoring production conditions. High-temperature biochars (above 800°C) provide greater carbon purity and stability, while mid-temperature biochars maintain reactivity essential for reduction reactions in furnaces.

The potential environmental benefit is significant: biochar production and use can be nearly carbon-neutral, as the Carbon Dioxide released during use is offset by carbon absorbed during biomass growth.

Where Biochar Fits in the Metallurgical Chain

1) Coke Making and Substitution

In blast furnaces, coke acts both as a structural scaffold and as a carbon reductant. Biochar’s lower density and compressive strength limit full substitution, but partial blending (up to 20%) can reduce fossil use without affecting furnace stability.

2) Pulverised Coal Injection (PCI)

Biochar performs particularly well as a pulverised fuel injected into the blast furnace raceway. Since structural integrity is not required here, substitution rates up to 100% have been demonstrated at pilot scale, offering an immediate route to emission reduction.

3) Iron Ore Sintering

Replacing 30 to 40% of the coke breeze with biochar during sintering cuts both Carbon Dioxide and air pollutant emissions, without compromising sinter strength or yield. The reduction in sulphur and nitrogen oxides provides an added environmental gain.

4) Electric Arc Furnaces (EAF)

In EAF operations, biochar can serve as a heating fuel and a carbon source for slag foaming, with minimal process disruption. As scrap-based steelmaking grows, EAFs represent a strong entry point for biochar adoption.

5) Non-Ferrous Metallurgy

Biochar’s reducing capability also extends beyond steel. Trials in copper, zinc, and lead recovery from smelting dusts show comparable metal yields to anthracite, demonstrating its versatility in metal recycling and waste treatment.

Barriers to Scale

Despite strong technical promise, the transition to biochar faces tangible challenges:

Physical limitations – Biochar lacks the density and strength of metallurgical coke.
Inconsistent chemistry – Feedstock variability affects ash composition, impurities, and reactivity.
Cost – Production costs range between USD 450 to 870 per tonne, compared with coal at roughly USD 180.
Feedstock logistics – Sustainable biomass supply chains are essential to prevent land-use competition.
Process adaptation – Existing furnace systems need modification to accommodate biochar’s physical and combustion behaviour.

Quality assurance is also key, as some biochars contain trace metals or alkali elements that can alter slag chemistry or emission profiles.

Bridging to a Low-Carbon Future

Biochar is unlikely to replace coke entirely in the near term, but it offers an immediate, scalable pathway for incremental decarbonisation. By displacing even part of the fossil carbon in steelmaking, it can cut process emissions by 10 to 40%, depending on application and substitution level.

Future research and industrial collaboration should focus on standardising biochar specifications for metallurgical use, improving densification and pelletisation techniques, demonstrating large-scale pilot integration in existing steel plants and conducting life-cycle and techno-economic analyses to ensure net benefits

As hydrogen direct reduction and carbon capture technologies mature, biochar can serve as an essential bridge solution, decarbonising today’s furnaces while paving the way for tomorrow’s green steel.