topics|Iron clad

Green Steelmaking

Steelmaking is responsible for about 8% of anthropogenic greenhouse-gas emissions—more than three times the amount released by civil aviation. Efforts to decarbonise the industry centre on replacing the carbon-based reducing agents used in conventional ironmaking.

Conventional process

In conventional steelmaking, iron ore reacts with reducing agents that strip away the oxygen. These are either carbon monoxide produced by the partial combustion of coke, or a mixture of hydrogen and carbon monoxide created by reacting methane from natural gas with steam. The reaction with carbon monoxide produces CO2; the reaction with hydrogen produces water. The resulting iron is full of impurities—especially silica, alumina and phosphorus—and must be processed further to remove these and lower its carbon content.

Established-firm approach

Companies such as ArcelorMittal and Thyssenkrupp have pursued the use of expensive electrolytically generated hydrogen as the reducing agent.

Startup approaches

Three startups are pursuing alternatives:

Electra (Boulder, Colorado) dissolves ore in sulphuric acid and electrolyses the solution at around 60°C, plating pure iron onto an electrode. It cuts out the middle man by using electricity directly rather than for generating hydrogen.
Boston Metal (Woburn, Massachusetts) uses molten oxide electrolysis at temperatures above 1,538°C. The firm suffered a critical equipment failure at its Brazil facility in February 2026 and has scaled back.
Hertha uses methane pyrolysis to produce hydrogen and carbon, then injects both into an electric-arc furnace. Its hydrogen-generation process is cheaper than electrolysis, and the use of an off-the-shelf furnace allows faster scaling.