Sponge iron production is a technical of purifying iron ore by reacting it with gas mixtures to remove oxygen via a reduction process. Iron ore from the ground is a chemical compound of iron and oxygen called ferric oxide, which is similar to rust. At the temperature of 1800 degree F, molecular oxygen can be removed from the iron by passing mixtures of hydrogen and carbon monoxide gas through the ore, which reduce the ore to a purified iron.

     High temperature is needed to chemically unlock the oxygen from the iron and allow it to react with the hydrogen and carbon dioxide. Sponge iron production can occure in different types of reactors. But a typical method is to use a horizontal rotary kiln. This equipment is a horizontal heated drum placed at a slight angle from level, which allows the iron ore to move slowly from one end to the others as the drum rotates. The drum is heated and gases are passed though the center of the drum, allowing the oxygen reduction to occure.

    Sponge ore production can use iron ore of varying sizes, with most ore feeding the kiln being sized from chunks to pellets. Temperature control of the kiln is important, because the iron must not be heated to melting temperature, only to levels needed to release oxygen. The iron leaving a sponge iron production process contains only a few percent impurities, including some small quantities of other metals found in the iron ore.

   Sponge ore can be further purified after the reduction reaction step, by passing the cooled iron through magnetic separators. Iron can be attracted by a magnet, so one the ore leaves the reactor, magnets can pull the sponge iron away from any impurities. This step can be important when coal is used as the reducing medium, because the reacted coal can contain non-metallic charcoal and other impurities. Removing them will further improve the efficiency of the blast furnace and require less processing in later steps.