extraction of aluminium

EXTRACTION OF METAL FROM ITS

OREPrepared by

Nor Dahlia ZamaniNurul Nadiah Bt Kamal

Aluminium is extracted by electrolysis. The aluminium oxide is dissolve in

molten cryolite and then reduced to the pure metal.

The first stage is the removal of the impurities, sand and some iron oxide.

The pure aluminium oxide left is called alumina.

Electricity is passed tgrough the alumina solution via electrodes.

The electrode that is connected to the positive terminal is called the anode.

The negative electrode is called the cathode.

Both these electrodes are made of graphite.

The reaction at the cathode — the negative terminal is

Al3+ + 3 e− → Al At the positive electrode (anode),

oxygen is formed:2 O2− → O2 + 4 e−

the whole process requires a great deal of electricity, which makes it very expensive.

Electrolysis of pure alumina (Hall-Heroult process)

fig 8.3 - Hall's cell

Refining of aluminium (Hoopes process) The metal obtained in the above step is about

99% pure and for most purposes it is taken as pure metal.

However, further purification of aluminium can be carried out by Hoopes process. The cell consists of an iron tank lined with carbon at the bottom.

A molten alloy of copper, crude aluminium and silicon is used as the anode. It forms the lower most layer in the cell.

The middle layer consists of molten mixture of fluorides, of sodium aluminium and barium (cryolite + BaF2). The upper most layer consists of molten aluminium. A set if graphite rods dipping in molten aluminium serve as cathode.

Uses Properties

Overhead electric cables Low density, lightResistant to corrosion (protected by aluminium oxide)Good electrical conductivity

Food containers Non-toxicResistant to corrosion Good conductor of heat

Aircraft bodyLow density, lightHigh tensile strengthResistant to corrosion

We mine iron ore from iron mines. Iron ore (haematite) is iron (iii) oxide, Fe2O3.

Carbon, C is the main reducing agent in the metal extraction process.

The extraction is carried out in a blast furnace. The metal ore is mixed with coke and limestone, CaCO3 .

Hot water is pumped into the blast furnace to burn the carbon and produce carbon monoxide, CO.

2C + O2 → 2CO

Fe2O3 + 3CO → 2Fe + 3CO2

2Fe2O3 + 3C → 4Fe +3CO2

Limestone or calcium carbonate, CaCO3 reacts with impurities such as silica in

the metal ores. Slag is formed. CaCO3 + SiO2 → CaSiO3 + CO2

Slag floats on top of the molten metal and is removed. The molten metal is collected at the bottom part of the blast furnace.

Extracting iron in industry

• Making useful steel for construction, automobiles, and other forms of transportation such as trucks, trains and train tracks.

• Powdered iron: used in metallurgy products, magnets, high-frequency cores, auto parts, catalyst.

• Radioactive iron (iron 59): in medicine, tracer element in biochemical and metallurgical research.

-THE END-