Getting Metals from Rocks
A metal ore is a rock, containing enough metal to make it worthwhile extracting metal from it.
In most cases the ore is an oxide of the metal; for example the aluminium ore is called bauxite
Most metals need to be extracted using a chemical reaction.
The economics of metal extraction can change over time. For example:
- If the market price drops a lot, it might not be worth extracting it.
- If the price increases a lot then it might be worth extracting more of it.
- As the technology improves, it becomes possible to extract more metal from a sample of rock than was originally possible. So it might now be worth extracting metal that wasn't worth extracting in the past.
Methods of Extraction
- Metal can be extracted chemically by reduction or by electrolysis
- Some ores may have to be concentrated before the metal is extracted this just involves getting rid of the unwanted rocky material.
- Electrolysis can also be used to purify the extracted metal.
Metals can be extracted by reduction using carbon.
When an ore is reduced , oxygen is removed.
The position of the metal in the reactivity series determines whether it can be extracted by reduction with Carbon.
Metals higher than Carbon have to be extracted using electrolysis, which is expensive.
Metals below Carbon can be extracted by reduction using Carbon. For example, iron oxide is reduced in a blast furnace to make iron. This is because C can only take the O away from metals which are less reactive than C itself.
Metals, more reactive than C have to be extracted using electrolysis of molten compounds.
The process is much more £££ than reduction with C becuase it uses a lot of energy (as high temperatures are required to melt the metals)
Electrolysis is the breaking down of a substance using electricity.
It requires a liquid to conduct the electricity, called the electrolyte.
Electrolytes are often metal salt solutions made from the ore or molten metal oxides.
The electrolyte has free ions-these conduct the electricity and allow the whole thing to work.
E- are taken away by the (+) anode and given away by the (-) cathode.
As ions gain or lose e- they become atoms or molecules and are released.
Copper and Electrolysis
Cu is easily extracted by reduction using C; the ore is heated in a furnace (smelting).
However the Cu produced is impure which does not conduct electricity v.well. This isn't v.useful because a lot of Cu is used to make electrical wiring.
So electrolysis is used to purify it though it is quite expensive, and it produces v. pure Cu, which is a much better conductor.
E- are pulled off Cu atoms at the anode, causing them to go into solution as Cu 2+ ions.
Cu 2+ ions near the cathode gain e- and turn back into Cu atoms.
The impurities are dropped at the anode as a sludge, whilst pure Cu atoms bond to the cathode.
The cathode starts as a thin piece of pure Cu and more pure Cu adds to it.
The electrolyte is Cu(II) sulfate solution containing Cu 2+ ions.