Getting Metals From Rocks

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Getting Metals from Rocks.

Ores contain enough metal to make extraction worthwhile.

1) A metal ore is a rock which contains enough metal to make it worthwhile extracting from.

2) In many cases, the ore is an oxide of the metal. For example: the metal ore of aluminium is called bauxite (Al2O3), which is aluminum oxide.

3) Most metals need to be extracted from their ores using a chemical reaction.

4) The economics of metal extraction can change over time, e.g:

if the market price of metal drops a lot it might not be worth extracting it.

if the price of the metal increases a lot it might be worth extracting more of it.

as 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 metals that weren't worth extracting in the past.

Metals are extracted from their ores chemically.

1) A metal can be extracted from its ore chemically - by reduction or by electrolysis (splitting with electricity).

2) Some ores may have to be concentrated before the metal is extracted - this just involves getting rid of the unwanted rocky material.

3) Electrolysis can also be used to purify the extracted metal.

Some metals can be extracted by reduction with carbon.

1) A metal can be extracted from its ore chemically by reduction using carbon.

2) When an ore is reduced, oxygen is removed from it, e.g:

2Fe2O3 + 3C → 4Fe + 3CO2

3) The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon.

a - Metals higher than carbon in the reactivity series have to be extracted using electrolysis, which is expensive.

b - Metals below carbon in the reactivity series can be extracted by reduction using carbon. For example, iron oxide is reduced in a blast furnace to make iron. This is because carbon can only take the oxygen away from metals which are less reactive than carbon itself.

The Reactivity Series.

Potassium K most reactive

Sodium Na

Calcium Ca

Magnesium Mg

Aluminium Al

CARBON C

Zinc Zn

Iron Fe

Tin Sn

Copper Cu least reactive

Some metals have to be extracted by electrolysis.

1) Metals that are more reactive than carbon have to be extracted using electrolysis of molten compounds.

2) An example of a metal that has to be extracted this way is aluminium.

3) This process is much more expensive than reduction with carbon because it uses a lot of energy. e.g: a high temperature is needed to melt aluminum oxide so that aluminium can be extracted - this requires a lot of energy which makes it an expensive process.

Copper is purified by electrolysis.

1) Copper can be easily extracted by reduction with carbon. The ore is heated in a furnace - this is called smelting.

2) However, the copper produced this way is impure - impure copper doesn't conduct electricity very well. This isn't very useful because copper is used to make electrical wiring.

3) So electrolysis is also used to purify it, even though it's quite expensive.

4) This produces very pure copper, which is a much better conductor.

Electrolysis means "splitting up with electricity".

1) Electrolysis is the breaking down of a substance using electricity.

2) It requires a liquid to conduct the electricity called the electrolyte.

3) Electrolytes are often metal salt solutions made from the ore (e.g. copper sulfate) or molten metal oxides.

4) The electrolyte has free ions - these conduct the electricity and allow the whole thing to work.

5) Electrons are taken away by the (positive) anode and given away by the (negative) cathode.

As ions gain or lose electrons they become atoms or molecules and are released.

Electrolysis is used to get copper:

1) Electrons are pulled off copper atoms at the anode, causing them to go into the solution as Cu2+ ions.

2) Cu2+ ions near the cathode gain electrons and turn back into copper atoms.

3) The impurities are dropped at the anode as a sludge, whilst pure copper atoms bond to the cathode.

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