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Copper in health
 From ore to copper 
On the previous page, we introduced the main stages in producing copper. Here we will look at the steps before any chemical reactions take place.

Photo of open pit mine
Picture 3. An open pit mine. The size of the huge lorries give you an idea of the scale.
Mining
Copper can be extracted from its ore by:

1. Traditional mining

underground sinking a vertical shaft into the Earth to an appropriate depth and driving horizontal tunnels into the ore.
open pit 90% of ore is mined by this method. Ores near the surface can be quarried after removal of the surface layers.

2. Leaching

The ore is treated with dilute sulphuric acid. This trickles slowly through the ore dissolving copper to form copper sulphate. The copper is recovered by electrolytic refining. Advantages of this process are:

  • much less energy is use than in traditional mining
  • no waste gases are given off
  • it can be used on ores with as little as 0.1% copper - for this reason, leaching extraction is growing in importance.

Map of world production
Picture 4. Map of copper production. Compare this with the pie chart of production.
Interactive photo of minerals
Picture 5 . Cuprite mineral and a close up of malachite.
What's in an ore?
There are many types of copper ore found throughout the world. Picture 4 shows the distribution of these deposits. About 80% of all copper extracted comes from sulphide ores.

A typical ore contains only 0.5% to 2.0% copper. It is a measure of the value of copper that it is worth extracting it from such small concentrations. The ore is a mixture of minerals and rock (called gangue). The most common copper minerals are:

Mineral Formula Appearance
% copper in
mineral
Cuprite Cu2O Red, earthy
see Qn 2
Chalcocite Cu2S Dark grey, metallic
see Qn 2
Bornite Cu5FeS4 Golden brown, metallic
63
Malachite CuCO3Cu(OH)4 Bright green, earthy
58
Azurite 2CuCO3Cu(OH)4 Blue, glassy
55
Chalcopyrite CuFeS2 Golden yellow, metallic
35

The first step is to physically remove the gangue.

Interactive graphic of froth flotation
Picture 6 . Froth flotation.
Concentrating the ore
The ore is crushed, ground and then enriched (concentrated) by Froth Flotation.

The powdered ore is mixed with a special paraffin oil which makes the copper mineral particles water repellent. It is then fed into a bath of water containing a foaming agent which produces a kind of bubble bath.

When jets of air are forced up through the bath, the water repellent copper mineral particles are picked up by the bubbles of foam. They float to the surface making a froth. The unwanted waste rock (gangue) falls to the bottom and is removed.

The froth is skimmed off the surface and the enriched ore (mainly the copper mineral) is taken away for roasting. The mixture of water, foaming agent and paraffin is recycled.

After this stage the enriched ore now contains about 25% copper by mass.

Question 2
Copper minerals are grouped as either sulphide or oxide. Look at the minerals below. In each case, decide which type of mineral it is. Then select the appropriate column.

For cuprite and chalcocite, calculate the % by mass of copper in each mineral (to the nearest whole percent).

Ore % Cu sulphide oxide
Cuprite
Chalcocite
Azurite
Chalcopyrite
Malachite
Bornite

The molar masses are: Ar(Cu) = 64; Ar(O) = 16; Ar(S) = 32.

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