10.08.03 Extracting Metals

Syllabus

- Unreactive metals such as Gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.
- Metals less reactive than Carbon can be extracted from their Oxides by Reduction with Carbon (smelting).
- Reduction involves the loss of Oxygen.

Knowledge and understanding are limited to the reduction of oxides using Carbon.
Knowledge of the details of processes used in the extraction of metals is not required.
- Students should be able to:

1. interpret or evaluate specific metal extraction processes when given appropriate information
2. identify the substances which are oxidised or reduced in terms of gain or loss of Oxygen.

What does this mean?

Why can't all metals be extracted with the same method?

You've seen the Reactivity series before but may never have wondered why we put Carbon on it even though Carbon is not a metal element.

But it's all to do with how we "make" metals.

Only very unreactive metals like Gold are found in the ground as elements.

A Gold nugget may be found in soil or stuck inside Quartz like the one below.

Gold vein in Quartz

More reactive metals are found as compounds mixed in with rocks.

We call rocks with useful amounts of metal compounds in them Ores.

This lump of Iron ore doesn't contain any Iron Metal.

But it does contain a lot of Iron Oxide.

To get at the Iron we need to remove the Oxygen by mixing it with a more reactive element that the Oxygen will "prefer" to bond to.

And this is where the Carbon comes in.

People have always had access to Carbon in the form of charcoal and then from coal.

If the Carbon and the Iron Oxide are heated strongly enough then smelting takes place - the Iron Oxide is reduced to Iron while the Carbon is oxidised to Carbon Dioxide.

Iron Oxide + Carbon --> Iron + Carbon Dioxide

Note to Mr Clewlow: We don't need to teach the Blast Furnace any more!!!!!!!!!!!!!!

Iron Ore

Liquid Iron after smelting in a furnace

Smelting was discovered thousands of years ago.

The more reactive a metal is the harder it is to remove the Oxygen.

So people discovered how to make Lead and Copper and Tin thousands of years before they worked out how to make Iron

But even the Romans could make all the metals up to Zinc.

However, they'd never have been able to make Magnesium or Potassium

How do we extract reactive Metals

Aluminium compounds are common in rocks but no one saw Aluminium metal until the Nineteenth century because it's too reactive to "split apart" from the Oxygen in Aluminium Oxide.

But then electricity was discovered.

Electrolysis is the process of splitting up ionic compounds using dc current.

Aluminium Oxide (like all metal oxides) is ionic.

So, provided that we can make it conduct we can split it up into Aluminium and Oxygen.

Aluminium Oxide --> Aluminium + Oxygen

2 Al2O3 --> 4 Al + 3 O2

Unfortunately, ionic compounds don't conduct unless they are dissolved or melted.

And Aluminium Oxide doesn't dissolve so we have to melt it before electrolysing it.

Which makes Aluminium very expensive compared to metals that can be smelted with Carbon.

Details of how this process is carried out are required but are taught later.

Aluminium Ore (Bauxite) being mined.

It has a high Aluminium Oxide content

Suggesting a method of metal extraction

You don't need to know where on the Series every metal comes.

But given an extended Reactivity Series, you should be able to suggest an extraction method for anything on it.

You may never have heard of Palladium but it's not much more reactive than Gold it's possible that it might be found in the ground as a metal rather than an ore.

You may never have heard of Antimony but it's more reactive than Copper so it would be found in the ground as an ore but could be extracted by smelting with Carbon.

You may never have heard of Strontium but it's more reactive than Aluminium so it would be found in the ground as an ore and couldn't be extracted by smelting with Carbon so we would have to use Electrolysis.

If you're told that Barium is extracted by electrolysis then you know that it would be towards the top of the Series, but not exactly where.

If you're told the Mercury exists as ores that can be turned into Mercury by heating a little then we know that it must be more reactive than Gold but less reactive than Copper that needs to be smelted.

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