Raw Materials
The three basic materials utilized in iron and steel making are iron or, limestone & coke. Iron does not occur in a free state in nature; still this is one of the most abundant elements, making up about 5 % of the earth’s crust in the form of several ores. The principal iron ores are taconite (a black flintlike rock), hematite (an iron oxide mineral) and limonite (an iron oxide containing water). After this is mined, the iron ore is crushed into fine particles, the impurities are removed by many means (such as magnetic separation), and this is formed into pallets, balls, or briquettes by using binders and water. Typically, pellets are about 65 % pure iron and 25 mm in diameter. The concentrated iron ore is referred to as beneficiated. Some iron-rich ores are utilized directly without palletising.
Coke is obtained from special grades of bituminous coal, which are heated in vertical coke ovens to temperatures of 1150oC and cooled with water in quenching towers. Coke has many functions in steel making. One is to generate the high level of heat needed for chemical reactions to take place in iron making. Second, it generates carbon monoxide (a reducing gas) which is then utilized to reduce iron oxide to iron. The chemical by- products of coke are used in making plastics and chemical compounds. Coke oven gases are utilized like as fuel for plant operations, & power generations.
The function of limestone (calcium carbonates) is to eliminate impurities from the molten iron. The limestone reacts chemically having impurities, action as a flux that causes the impurities to melt at a low temperature. The limestone combines having the impurities and forms a slag that is light & floats over the molten metal. Slag is subsequently eliminated. Dolmite (an ore of calcium magnesium carbonate) is also utilized as a flux. The slag is later utilized for making cement, glass, fertilizers, rock wool insulation, building materials, and road ballast.