MYP 10 : The extraction of metals


Iron

Extracted by the Blast furnace or Bessemer process.

Raw materials

Each of the raw materials is necessary for the production - click to see its purpose

The blast furnace

The iron ore, coke and limestone ("charge") is fed into the blast furnace from the top. Once inside the hot furnace the coke reacts with the blast of air (containing oxygen) making carbon monoxide gas. This gas is very reactive and has a great desire for more oxygen which it finds in the iron ore. The oxygen atoms bond to the carbon monoxide making carbon dioxide and iron is produced as a molten liquid metal. This molten iron can be tapped off from the bottom of the furnace.

Removal of impurities

Iron ore often has silicon dioxide (sand) impurity which must be removed during the process. To do this limestone is added to the charge. The limestone (chemically, calcium carbonate) decomposes in the heat of the furnace to calcium oxide. This calcium oxide can then react with the hot sand (silicon dioxide) making a chemical called calcium silicate (slag). This calcium silicate is a very light molten liquid which floats to the top of the reaction mixture and can be tapped off from above the molten iron. It is solidified by cooling and used for manufacture of building materials (brieze blocks).

Reduction of metal ores - chemistry

The process of removal of elements combined with metals to obtain the pure metal is called reduction. The element removed is usually oxygen (as in the case of iron oxide being reduced to iron) but it may be other elements as well. In general the word reduction is used for processes of removal of oxygen. From the point of view of the metal particles, they start off as ions in the original ore (metals always exist as positive ions in chemical compounds) and end up as metal atoms. The metal particles undergo the following change:

M2+ + 2e M

The process of reduction, therefore, involves the addition of electrons to metal ions.

In summary reduction may be thought of as:

The chemical compound causing the reduction is called the reducing agent. In the blast furnace the reducing agent is the carbon monoxide although some books may refer to the carbon (coke) as the reducing agent this is not strictly speaking correct.