In addition to the blast furnace process, where liquid pig iron is produced directly, direct reduction processes are also used in which the iron ore is reduced to sponge iron.
Direct reduction takes place in a shaft furnace, which is filled with lump ore and pellets from above. The separation of oxygen from the iron ore is carried out with a reducing gas (carbon monoxide and hydrogen gases), which flows from bottom to top. In contrast to the blast furnace process, the reduction of iron ore takes place at temperatures of 700 to a maximum of 1000°C. In this process, no molten pig iron is produced because the iron ore is not melted, only the oxygen is separated from it. The final product is called sponge iron and consists of up to 85% pure iron. The sponge iron is cooled in the lower part of the shaft furnace in order to prevent a later strong re-oxidation in air. The piece-shaped iron sponges are then smelted to liquid pig iron, usually in an electric arc furnace.