Production of Iron and Steel

Raw Materials

The three basic materials used in iron- and steelmaking are iron ore, limestone, and coke. Although it does not occur in a free state in nature, iron is one of the most abundant elements in the World, making up about 5% of the earth’s crust (in the form of various ores). The principal iron ores are taconite (a black flintlike rock),/vematite (an iron-oxide mineral), and limonite (an iron oxide containing water).After it is mined, the ore is crushed into fine particles, the impurities are removed by various means (such as magnetic separation), and the ore is formed into pellets,balls, or briquettes using water and various binders. Typically, pellets are about 65% pure iron and about 25 mm in diameter. The concentrated iron ore is referred to as benejqciated (as are other concentrated ores). Some iron-rich ores are used directly, without pelletizing.

Coke is obtained from special grades of bituminous coal (a soft coal rich in volatile hydrocarbons and tars) that are heated in vertical ovens to temperatures of up to 1150°C and then cooled with Water in quenching towers. Coke has several functions in steelmaking, including (a) generating the high level of heat required for
the chemical reactions in ironmaking to take place and (b) producing carbon monoxide (a reducing gas, meaning that it removes oxygen), which is then used to reduce iron oxide to iron. The chemical by-products of coke are used in the synthesis of plastics and of chemical compounds. The gases evolved during the conversion of coal to coke are used as fuel for plant operations.

The function of limestone (calcium carbonate) is to remove impurities from the molten iron. The limestone reacts chemically with impurities, acting like a flux (meaning to flow as a fluid) that causes the impurities to melt at a low temperature. The limestone combines with the impurities and forms a slag (Which is light),floats over the molten metal, and, subsequently, is removed. Dolomite (an ore of calcium magnesium carbonate) also is used as a flux. The slag is used later in making cement, fertilizers, glass, building materials, rock-Wool insulation, and road ballast.