The iron is extracted by reduction in a blast furnace. The reducing agent is carbon monoxide. A charge of iron ore, coke and limestone is put in the top of the furnace.
Hot air is blown in near the bottom.
The coke burns in the air to form carbon dioxide and releasing much of the heat needed for the process. As the carbon dioxide passes up through more hot coke it is reduced to carbon monoxide. The carbon monoxide reduces the iron oxide to iron. It decomposes in the furnace to form calcium oxide, which reacts with acidic impurities in the ore such as sand, to form a slag, which separates from the molten iron at the bottom of the furnace.