8.1 Mining and mineral processing  (Page 5/7)

$C+O_2\to C{O}_2$

$C{O}_2+C\to 2CO$

STEP 2: Reduction of iron oxides takes place in a number of stages to produce iron.

$3F{e}_2{O}_3+CO\to 2F{e}_3{O}_4+C{O}_2$

$F{e}_3{O}_4+CO\to 3FeO+C{O}_2$

$FeO+CO\to Fe+C{O}_2$

STEP 3: Fluxing

The flux is used to melt impurities in the ore. A common flux is limestone (CaCO ${}_3$ ). Common impurities are silica, phosphorus (makes steel brittle), aluminium and sulfur (produces SO ${}_2$ gases during smelting and interferes with the smellting process).

$CaC{O}_3\to CaO+C{O}_2$

$CaO+Si{O}_2\to CaSi{O}_3$

In step 3, the calcium carbonate breaks down into calcium oxide and carbon dioxide. The calcium oxide then reacts with silicon dioxide (the impurity) to form a slag . In this case the slag is the CaSiO ${}_3$ . The slag melts in the furnace, whereas the silicon dioxide would not have, and floats on the more dense iron. This can then be separated and removed.

Types of iron

Iron is the most used of all the metals. Its combination of low cost and high strength make it very important in applications such as industry, automobiles, the hulls of large ships and in the structural components of buildings. Some of the different forms that iron can take include:

• Pig iron is raw iron and is the direct product when iron ore and coke are smelted. It has between 4% and 5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is an intermediate step between iron ore, cast iron and steel.
• Wrought iron is commercially pure iron and contains less than 0.2% carbon. It is tough, malleable and ductile. Wrought iron does not rust quickly when it is used outdoors. It has mostly been replaced by mild steel for 'wrought iron' gates and blacksmithing. Mild steel does not have the same corrosion resistance as true wrought iron, but is cheaper and more widely available.
• Steel is an alloy made mostly of iron, but also containing a small amount of carbon. Elements other than carbon can also be used to make alloy steels. These include manganese and tungsten. By varying the amounts of the alloy elements in the steel, the following characteristics can be altered: hardness, elasticity, ductility and tensile strength.
• Corrugated iron is actually sheets of galvanised steel that have been rolled to give them a corrugated pattern. Corrugated iron is a common building material.

One problem with iron and steel is that pure iron and most of its alloys rust. These products therefore need to be protected from water and oxygen, and this is done through painting, galvanisation and plastic coating.

Iron in south africa

The primary steel industry is an important part of the South African economy and it generates a great deal of foreign exchange.