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Iron ores

RAW MATERIALS

Raw and starting materials required for the production of iron and steel can be broken down into the following groups: ferrous materials (iron ores, scrap); fuels and reducing agents (coke, coal, oil, gas); fluxes and additions (lime, alloying agents).

The most important raw materials for iron and steelmaking are the ferrous materials that provide the source of the iron.

Iron ores

Among the elements in the earth's crust, iron [Fe] with an occurrence of about 5.6% ranks fourth below oxygen, silicon and aluminum.

The data of the US Geological Service on the world's iron reserves published in 1998 indicate that the reserves of crude iron ore currently regarded as economically extractable under today's criteria amount to 140 billion tons, a figure which, given current production volumes, should last for approx. 100 years. These global figures do not, however, differentiate between high-grade, rich ores and low-grade, lean ores.

Iron does not occur in its pure form in nature, but only in the form of chemical compounds. The most frequent of these are the iron-oxygen compounds (iron oxides). Iron oxides are always mixed with impurities known as "gangue". This mixture of iron oxides and gangue is classified as iron ore where economic production is possible. The gangue content plays an important role in the processing of the iron ores. If the gangue primarily contains lime (CaCO3), the ore is termed "basic", while if silica (SiCO) predominates, the ore is said to be "acidic".

Further impurities include aluminas and phosphates.

The appearance of iron ore varies considerably depending on the type of deposit. Iron ores usually take the form of a hard, rocky mass. The colour of iron ore generally range from reddish or brownish shades to a metallic black.

The weight of an iron ore is largely determined by the iron content.



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