Direct reduced iron

The production of DRI involves the removal of oxygen from iron ore (hematite or magnetite) using a reducing gas, typically a mixture of hydrogen and carbon monoxide derived from natural gas reforming or coal gasification. The reduction occurs in the solid state, preserving the ore's morphology and resulting in a porous product. The two dominant commercial processes are the Midrex and HYL/Energiron shaft furnaces, which together account for the majority of global output. In these reactors, iron ore pellets or lump ore descend counter-current to the hot reducing gas, achieving metallization degrees of 90–95%. The chemistry follows the stepwise reduction of Fe₂O₃ to Fe₃O₄, then to FeO, and finally to metallic Fe. The use of hydrogen as a reductant produces water vapor instead of CO₂, making hydrogen-based DRI a cornerstone of green steel initiatives.

DRI is primarily used as a premium scrap substitute in electric arc furnaces, where its consistent chemistry and low residual element content (such as copper and tin) allow for the production of high-quality steels. It is also compacted into hot briquetted iron (HBI) for easier transport and handling. Compared to pig iron from a blast furnace, DRI production emits significantly less CO₂ when natural gas is used, and near-zero emissions when green hydrogen is employed. This positions DRI as a critical enabler for the steel industry's transition to meet climate targets. Additionally, DRI can be charged into blast furnaces to reduce coke consumption, a practice known as top-gas recycling or tuyere injection, which improves efficiency and lowers emissions.²

Global DRI production reached approximately 135 million tonnes in 2023, with India, Iran, Russia, and Saudi Arabia as leading producers.³ India relies heavily on coal-based rotary kiln processes, while the Middle East and Russia use gas-based shaft furnaces. The growth of DRI is closely tied to the availability of cheap natural gas and the expansion of EAF steelmaking. In recent years, several pilot and commercial projects have demonstrated hydrogen-based DRI, such as HYBRIT in Sweden and Midrex's hydrogen-ready plants. These initiatives are part of broader decarbonization roadmaps, with the International Energy Agency projecting that hydrogen-based DRI could account for a significant share of primary steel production by 2050.⁴

Beyond its mainstream use, DRI has several niche dimensions. For instance, the term 'sponge iron' originates from the porous structure that resembles a sponge, and this porosity makes DRI susceptible to re-oxidation and self-heating during storage, requiring careful handling and passivation. In India, the coal-based DRI industry, known as 'kudremukh' or 'tata sponge', has faced environmental scrutiny due to high emissions and energy intensity. Another lesser-known fact is that DRI can be produced from iron ore fines using fluidized bed reactors, such as the FINMET process, which avoids the need for agglomeration. Additionally, DRI has been used in the production of wrought iron historically, and modern DRI is sometimes alloyed with nickel or chromium to produce stainless steel directly. The first commercial DRI plant, the HYL process, was developed in Mexico in 1957, predating the more common Midrex process.⁵

Metallization

The degree to which iron oxide has been reduced to metallic iron, typically expressed as a percentage.

Hot briquetted iron (HBI)

A compacted form of DRI produced at high temperature to reduce porosity and improve handling and transport safety.

Shaft furnace

A vertical reactor used in gas-based DRI processes where ore descends against a rising stream of reducing gas.