Industrial scale, iron ore is produced from a direct reduction reaction with carbon at temperatures of approx. 2000 ° C in furnace (blast furnace). This allows removing the influence of high temperature components of non-ferrous ore or earth. At the top of the furnace is inserted iron ore, coke and carbon in the form of a flow like calcium carbonate or dolomite, while the bottom is inspired by a current of hot air. Coke reacts with oxygen from the air stream, forming carbon monoxide.
Carbon monoxide reduces the iron ore (in this case below, hematite), turning it into molten iron and making carbon dioxide.
Flow helps to melt impurities in the ore, in particular silicon dioxide and silicates. Under the influence of heat from the furnace, calcium carbonate decomposes into calcium oxide and carbon dioxide.
Calcium oxide combines with silicon dioxide to form a slag which melts at the temperature of the furnace (which would not have happened with pure silicon dioxide).
Molten slag floats above the molten iron, denser, and these components can be disposed of separately through special openings in the furnace.
Result is actually useful material pig iron, containing approx. 4-5% carbon. This can be further reduced to obtain pure technical iron steel or in other furnaces or converters.
Chemical pure iron can be prepared by calcination of ferric hydroxide precipitate Fe (OH) 3 or other iron salts. and industrial scale by roasting iron salts with slight decomposition.