C1.3 Extracting Metals

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  • Created by: Fiona S
  • Created on: 01-04-15 22:57

Where do metals come from?

They are found in the Earth's crust. We find most metals combined chemically with other chemical elements, often with oxygen. So the metal must be chemically separated from its compound before you can use it. 

In some places, there's enough of a metal or metal compound in a rock to make it worth extracting the metal. We call this rock an ore. Ores are mined from the ground.
Some need to be concentrated before the metal is extracted and purified.

Whether it is worth extracting a particular metal depends on:

  • How easy it is to extract from its ore
  • How much metal the ore contains

A few metals, such as gold and silver, are so unreactive that they are found in the earth as metals themselves. We say they exist in their native state.

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How do we extract metals?

The way in which we extract metals depends on its position on the reactivity series. 

A more reactive metal will displace a less reactive metal from its compounds.

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Extraction of Iron

Main reactions in a blast furnace..

Iron Oxide + Carbon --> Carbon Dioxide + Iron

Oxidation is when a substance gains oxygen or loses hydrogen.

Reduction is when a substance loses oxygen and gains hydrogen.

The carbon reduces iron oxide to form iron. This means carbon is the reducing agent for iron oxide (carbon is more reactive than iron as it can displace the oxygen from iron oxide to form iron).

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Process in Blast Furnace

1. Iron Ore (mainly iron oxide), Coke (form of Carbon) and limestone (Calcium Carbonate) are the 3 solids in the top of the Blast Furnace

2. Hot air is blasted from the bottom of the Blast Furnace

3. The coke burns in the hot air
         C + O --> CO2

4.At the temperature of the Blast Furnace (2000 degrees Celsius) other reactions happen
   e.g. CO2 + C --> 2CO(toxic)

5. Carbon Monoxide reduces the iron oxide to form iron
      Fe2O3 + 3CO --> 2Fe + 3CO2 molten iron runs out of bottom of the Blast Furnace

6. The limestone decomposes in the heat o the Blast Furnace.
   Calcium Carbonate --(thermal decomposition, 2000°C)-> Calcium + Carbon Dioxide

7. The calcium oxide is a base + neutralises the acidic, sandy, impurities in the iron ore
     Calcium Oxide + Silicon Dioxide --> Salt = Calcium Silicate, known as **** (used in road building)

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Blast Furnace

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Aluminium

Uses

  • Drinking cans and foil
  • Lamp posts and backing for headlight
  • CD and DVDs

Aluminium is...

  • Strong
  • Low density - light in weight
  • Behaves unreactive due to being covered in unreactive layer of aluminium oxide
  • Highly reactive - high in reactivity series - above carbon - so carbon canot remove oxygen from aluminium oxide
  • Expensive - it takes a lot of energy to extract it

Aluminium Ore ... is impure aluminium oxide. It is mined in France (Les Baux), Nigeria and West Africa.

Aluminium ore is called bauxite. It is red and contains white aluminium oxide and red impurities. It is obtained by open-cast mining.

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Aluminium

Advantages of open cast mining

  • Safer and cheaper

Disadvantages of open cast mining

  • Dust
  • Damage to habitats
  • Noise pollution
  • Lose of wildlife
  • Visual pollution

The purified aluminium oxide shipped to the UK where it is extracted by electrolysis.

Electrolysis involves melting the aluminium oxide and passing a lot of electricity through the molten oxide.

Aluminium Oxide --> Aluminium + Oxide

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Aluminium

Where would you site an aluminium extraction plant (aluminium smelters) in the UK?

  • On the coast so aluminium oxide can be imported by ship
  • Near a cheap electricity source
  • In north east Newcastle - coal available
  • In west highlands of Scotland - hydroelectric power lines
  • In Anglesey - nuclear power
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Extraction of Aluminium

Metals that are more reactive than Carbon, such as aluminium, are extracted by electrolysis of molten compounds.
Current methods of extracting are expensive because:

  • There are many stages in the process
  • Large amounts of energy are needed

(http://www.educationquizzes.com/library/GCSE/Chemistry/ManufacturingProcesses/Manufacturing-Processes-03-C.jpg)

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Extracting Copper

Copper can be extracted from copper rich ores by heating the ore in a furnace. This is often called smelting.

The copper is heated very strongly in a furnace with air to produce crude copper. For example:

Copper Sulphide + Oxygen --> Copper + Sulphur Dioxide

The copper attained is impure and of little use. To purify the copper electrolysis is used. The positive metal ions move towards the negative electrode.

Smelting and purifying ores uses huge amounts of heat and electricity. This costs a lot of money. Copper rich ores are being depleted and traditional mining and extraction have major environmental impacts.

In industry copper can be extracted from copper sulphate solution by adding SCRAP IRON. The iron is more reactive than copper, so it can DISPLACE copper from its solution.

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Extracting Copper from low grade ores

New ways of extracting copper from low grade ores are being researched to limit the environmental impact of traditional mining. Copper can be extracted by:

1. PHOTOMINING - this process uses plants to absorb metal compounds. The plants are burned to produce ash that contains metal compounds

2. BIOLEACHING - this process uses bacteria to produce leachate solutions that contain metal compounds

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Metal Alloys

Most metals in everyday use are alloys. Pure copper, gold, iron and aluminium are too soft for many uses and so are mixed with small amounts of similar metals to make them harder for everyday use.

Copper Alloys
We make brass by alloying copper with zinc. Brass is much harder than copper but it is workable. It can be hammered into sheets and pressed into intricate shapes. This property is used to make musical instruments

Aluminium Alloys
Aluminium has a low density for a metal and can be alloyed with a wide range of other elements. There's over 300 alloys of aluminium available, all have very diifferent properties. Some can be used to build aircraft while others can be used as armour plating on tanks and other military vehicles.

Gold Alloys
 We usually alloy gold with copper when we use it in jewellery. Pure gold wears away to easily. By varying the proportions of the two metals we also get different shades of gold objects.

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