DRI

Direct reduced iron is solid metallic iron produced by reducing iron ore with hydrogen or carbon monoxide gas, without reaching the melting point of iron. The process yields a porous, sponge-like material that still contains some gangue and unreacted oxides, yet contains 90 to 96 percent metallic iron by mass. DRI serves as a premium raw material for electric arc furnaces and forms part of the charge in oxygen-blown steelmaking processes.

The two dominant technologies are the shaft furnace method, common in India and the Middle East, and the rotary kiln process, used elsewhere. In shaft furnaces, lump ore or pellets fall downward through a column of reducing gas, typically syngas (a mixture of CO and H2) or natural gas. Rotary kilns tumble ore in a rotating drum while reducing gas flows through. Both methods operate between 650 and 900 degrees Celsius, well below iron's 1538-degree melting point. This low-temperature operation favors hydrogen-based reduction and makes DRI attractive for low-carbon steelmaking when green hydrogen becomes cost-competitive.

DRI's chief advantage is its high iron content relative to raw ore and its freedom from the fuel ash and slag that plague blast furnace iron. However, DRI oxidizes rapidly when exposed to wet air, forming rust and losing strength. This oxidation vulnerability has driven the development of hot-briquetted iron (HBI), which compresses hot DRI into dense, stable briquettes that resist reoxidation during storage and transport. In regions far from reduction plants, HBI extends the economic range of DRI-based steelmaking.

Global DRI production reached roughly 100 million tonnes per year by the 2020s, with India accounting for about 50 percent of output. India's abundance of iron ore, coal, and natural gas, combined with the shaft furnace's fuel efficiency, created a dominant position. The term DRI became standard in the 1970s as these processes industrialized; earlier steelmakers had called such material sponge iron or reduced ore.

Quality control focuses on metallic iron content, bulk density, and crushing strength. DRI pellets or lumps must withstand handling in furnaces without excessive breakage. Impurities such as phosphorus, sulfur, and zinc carry over from the ore and concentrate in the final steel if not controlled. Mills buying DRI typically specify iron content bands, size fractions, and maximum allowances for silica, alumina, and trace elements.