Extraction of Aluminium

Question 1

What is Bauxite?

Answer 1

The primary ore of aluminium

Question 2

How much Bauxite is needed to produce 1kg of aluminium?

Answer 2

4kg of Bauxite makes 1kg of Aluminium

Question 3

List the three stages of Aluminium extraction.

Answer 3

1. Bauxite mining (open pit or strip mining)
2. Alumina refining
3. Aluminium smelting

Question 4

List the 4 stages of Alumina refining.

Answer 4

1. Digestion
2. Clarification
3. Precipitation
4. Calcination

Question 5

List the 5 stages of Aluminium smelting

Answer 5

1. Add bath and alumina
2. Anode
3. Electrolysis
4. Tapping
5. Primary Casting

Question 6

Name the two impurities in Bauxite and the three methods of purification.

Answer 6

1. Fe2O3 (Iron (III) oxide)
2. SiO2 (silicon dioxide)

NOTE: type of impurity depends on mining location.

1. Hall-Heroult process -for high amounts of both impurities
2. Bayer process - for high amounts of iron oxides
3. Serpek method - for high amounts of silicon dioxide

Question 7

Why is cryolite added to aluminium ore?

Answer 7

To reduce the alumina melting temperature (from 2040 to 900 C) for a more practical electrolysis temperature of 950 C.

Question 8

Explain how aluminium is formed during electrolysis

Answer 8

Opposite charges attract. The positive aluminium ions move towards the negative cathode. At the cathode the ions gain electrons and turn into aluminium atoms.

Question 9

Explain how oxygen is formed during electrolysis

Answer 9

Negatively charged ions move to the anode. Here they lose 2 electrons and turn into neutral oxygen atoms. There atoms rapid join to form pairs of normal oxygen gas.

Question 10

Explain how carbon dioxide is formed during electrolysis.

Answer 10

At high temperatures, high amounts og oxygen react with the carbon anode. CO2 is formed and the anode is rapidly consumed, thus needs to be replaced frequently.

Question 11

Explain each digit in the XXXX designation for aluminium alloys.

Answer 11

1st digit - purity or alloy type
2nd digit - indicates modification of the alloy
3rd & 4th digit - indicate the purity

Question 12

What material is used for the electrodes?

Answer 12

Graphite - high levels of electrical conductivity and capable of sustaining the extremely high heat that is generated.

Question 13

List the 4 elements that have sufficient solubility to alloy with aluminium.

Answer 13

Copper, Zinc, Silicon and Magnesium

Question 14

Which two strengthening processes can be carried out on aluminium alloys (depending on the series)?

Answer 14

Either Work (strain) Hardening and Annealing or Solid Solution (age) hardening.