Модуль 1 заняття 4

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.

Types of Iron Ore

	Magnetite, magnetic iron ore, Fe3O4 . Magnetite (Fig. 13) is an iron ore that exhibits a high iron content (60 to 70%) and is extensively free from unwanted tramp elements. The gangue is mostly of a siliceous nature (acidic). Iron and oxygen atoms are very closely combined with each other in magnetite, thus making magnetite "difficult to reduce". As the name indicates, magnetite is highly magnetic. Large deposits are found in Sweden, Norway and Russia.
	Hematite, Red Iron Ore. Hematite (Fig. 14) likewise exhibits high Fe contents combined with low levels of phosphorus and sulphur, and a siliceous or clay gangue (acidic). The particular reddish colour is caused by the iron (III) oxide. In this red iron ore, the iron-oxygen compound is looser so that hematite is regarded as "easily reducible". Workable deposits are found in all parts of the world.

Limonite, Brown Iron Ore, Fe2o3 ·h2o

Limonite is "aqueous", i.e. the iron oxides have formed a stable compound with water (water crystallization). Limonite is the most widespread iron ore but usually contains only low concentrations of iron. Exploitation is only economically feasible if the deposits are fairly large.