Iron
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Iron

Iron is the most abundant of earth's elements although much of it constitutes the inner and outer cores. It makes up about 5% of the earth's crust and is found across a wide range of rock types and minerals, but does not occur naturally in pure form. Ores which contain at least 50% iron and which occur in seams of millions of tonnes suitable for open cast mining are currently considered economically viable for metallic iron production. Haematite and magnetite are commonly mined ores where they are found in layers of sedimentary rocks known as banded iron formations. The top three iron ore producing countries are China, Australia and Brazil.

After mining, the highest grade ores are sent direct for smelting. Lower grade ores first undergo processes such as washing, crushing and sintering to remove some of the unwanted elements. Traditionally, iron ores are heated up to melting point in a blast furnace together with coke and limestone. Chemical reactions produce slag, gases and molten iron at least 92% pure. This is either cooled down into bars of pig iron or sent directly as hot metal for further processing. The vast majority goes into steel making. The slag is used as a construction aggregate or cement and the gases are scrubbed clean before release into the atmosphere.

The basic process of refining in a blast furnace has remained unchanged for hundreds of years, although they have become larger and more efficient. Alternative processes have been developed which use less energy to produce metallic iron, however. Direct reduced iron (DRI), also known as sponge iron, is formed by using natural gases or gases derived from coal to reduce the oxygen from ferrous oxides at temperatures below the melting point of iron. DRI can be made into steel in an electric arc furnace. This method offers lower capital and operating costs than the traditional blast furnace. The disadvantages are that DRI quickly starts corroding if exposed to moisture and contains some impurities which have to be removed at a later stage requiring increased fuel consumption.
 

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