Extraction of metal from metal oxides

Metals are often found in nature combined with oxygen atoms, in the form of metal oxides. Thousands of years ago, we discovered how to take some of these metal oxides, and extract the metals... in pure form. Somehow, the oxygen atoms can be removed from the oxides. How?

We use the the fact that each different element has a different reactivity with oxygen. Here is a list of some metals, ordered by how easily they react with oxygen - a reactivity series. Of these metals, magnesium is the most reactive, while silver is the least reactive. If you take the oxide of one of the metals further down the list, such as copper... ... and you heat it together with a metal higher up in the list, such as iron...

What do you think will happen with the oxygen? The element that is less reactive started off as an oxide. In the reaction, the oxygen will go to the element that is more reactive. The metal lower in the list ends up as pure metal, while the metal higher in reactivity becomes an oxide. A metal anywhere in the list can remove oxygen from all the metals below it.

Lead can remove the oxygen from copper oxide and silver oxide, but not from zinc oxide. This makes it easier to extract metals that are further down this list, like silver or copper - than the ones higher up in the list, like aluminium or zinc. We'll add another element to the list: carbon - a non-metal. Why is there a non-metal in a list of metal reactivity? Because, just like the metallic elements in the series, carbon can also be used to remove oxygen, from the oxides of the metals below it in the list.

If we heat iron oxide with carbon for instance... The carbon will remove the oxygen from the iron - producing pure metallic iron. What happens to the oxygen? It attaches to the carbon, forming carbon dioxide. This also explains why different metals were discovered at different times throughout history.

They closely mirror the list of oxygen reactivity. Silver has been known since prehistoric times, since it can be found in almost pure form in nature. Copper has been used for some six thousand years; and lead about five thousand years. If you look at their places in the reactivity series, you can see why: They are both relatively easy to purify using the carbon in firewood, the temperature of a woodfire is high enough. Some three thousand years ago, blacksmiths discovered that they could use charcoal - which can produce higher temperatures than ordinary firewood - to extract metallic iron from iron oxides.

This process, called smelting, started the Iron Age. When it comes to elements that are above carbon in the reactivity series, it's much more difficult to extract them from their oxides. So although there is a lot of aluminium and magnesium in the Earth's crust, it wasn't until the 19th century - 200 years ago - that these metals were produced in their pure form, through the use of electricity. So: If... an oxide of a metal is heated enough, together with a more reactive element in this reactivity series...

The oxygen will attach to the more reactive element. That means that a metal that starts out as an oxide can be extracted in its pure, oxygen-free form.