What is an ore?
A rock which contains enough metal to make it economically worthwhile extracting the metal from it.
In most cases:
Most of the time the Ore of a metal is an Oxide of the metal because it has reacted with Oxygen. Eg. Aluminum oxide.
Some metals are so unreactive we mine them out of the ground in their pure form as they do not form ores. Eg. Gold.
There are two ways metals can be extracted:
Reduction - A displacement reaction using another more reactive metal or using carbon.
Electrolysis - Using electricity to split up the metal from it's impurities. Electrolysis can also be used to purify the extracted metals.
Reduction using a displacement reaction
Reducing a metal means removing the oxygen.
Some metals can be extracted using Carbon; the carbon is more reactive than the metal and steals its oxygen leaving the metal all on it's own... (which is what we want!).
Eg. Fe2O3 + C = Fe + CO2 Remember to balance it!
2Fe2O3 + 3C = 4Fe + 3CO2 That's better :)
Not all metals can be reduced using a displacement reaction
This is because sometimes the metal is more reactive than carbon so carbon can no longer steal the oxygen away from it.
How can we tell if we can use carbon to extract a metal?
The reactivity series - anything above carbon has to be extracted by electrolysis.
To extract metals that are more reactive than carbon we have to make them into a liquid and pass electricity through them. This liquid is called the electrolyte.
Electrolytes are often metal-salt solutions (eg. copper sulphate) or a molten metal oxide.
The Electrolytes have free electrons these conduct the electricity so everything can work.
Electrons are taken by the negative cathode from the positive anode. The positive anode (the one losing the electrons) is the impure metal; the impurities just fall away to the bottom as sludge as the ions clump together to become atoms or molecules.
Electrolosis much more expensive than using a displacement reaction as it requires alot more energy - High tempratures to melt the metal and lots of electricity.
Copper is less reactive than carbon so we can use a displacement reaction, however when we do this the copper is still impure and isn't very useful to us.
So we have to use electrolysis to purify it.
1) Electrons are pulled off the positive anode, they go into the solution as Cu2+
2) The Cu2+ ions near the negative cathode gain Electrons and turn back into copper atoms.
3) The impurities fall to the bottom as sludge, and the pure copper atoms bond to the negative cathode.
Alternative Copper displacement reaction
You can also use more reactive metals, instead of carbon, to take the impurities from the less reactive metals.
For example, we use scrap iron to displace copper because scrap iron is cheap.
Copper sulphate + Iron = Iron sulphate + Copper
Iron is more reactive so it steals the sulphate away from the copper and leaves the copper on it's own (yay!)
Bioleaching & Phytomining
We have to find new ways to extract copper from low grade ores as copper rich ores are running out.
One of the ways we do this is by bioleaching, this is using bacteria to break up the bonds between the copper and sulphate. The solution produced by the bacteria contains copper which can be removed by filtering.
Another way is phytomining, this involves growing pants in copper rich soil. The plants cant get rid of the copper so it builds up in the leaves. The plants are harvested and burned, the ash is collected. The copper is extracted from the ash.
Impacts of Extracting Metals!
- We can make useful products
- It provides local people with jobs and brings money to the area
- It causes noise
- scarring of the landscape
- Loss of habitats for animals
- The mine shafts can also be dangerous for a long time after they've been abandoned
Also, Ores are running out and it takes lots of energy to extract metals in the first place. So, what can we do about it? RECYCLE!!
Why Should we Recycle metals?
Mining and extracting metals take lots of energy, most of this energy comes from burning fossil fuels, with burning fossil fuels we get Carbon Dioxide, acid rain and global dimming which contributes to climate change.
So, RECYCLING helps to reduce this, it uses a very small fraction of the energy that's needed to get new metals; costs less too.
RECYCLING also helps to conserve the ores in the earth - so they don't get all used up and we find ourselves metal-less.
RECYCLING means less landfill. What's the point in spending all that energy and money to get a metal product, just to go and bury it in a landfill!
Properties of Transition Metals
The typical properties of transition metals:
Strong but still malleable - making them ideal for bridges and car bodies
Good conductor of heat - making them ideal for saucepans
Good conductor of electricity - making them ideal for electrical wires
Different metals are used for different things because they have specific properties.
For example, if you were making a replacement joint you would want a metal that doesn't corrode, was light and not too bendy. Titanium has these specific properties, so that's what we use.
However, after consistent use metals can get tired from having stresses and strains put on them repeatedly and become weaker. This is called metal fatigue and can be very dangerous.
1) Iron straight from a blast furnace after its displacement reaction with carbon contains way to much carbon, it's only 96% Iron. This Iron is not very useful because it's really brittle.
2) So, to make it bendy and not brittle we take all the carbon out so it becomes pure iron. This means the rows of iron atoms can slide over one eachother without carbon getting in the way, therefore it is bendy.
3) But, this pure iron is now too bendy! So we have to make it into a steel alloy.
An alloy is when we get a pure metal and add a little bit of another metal or non metal to change its properties and make it more useful.
We do this to pure iron to make it strong enough to be useful.
- Low carbon steel - 0.1% carbon - easily shaped - used for car bodies
- High carbon steel - 1.5% carbon - very hard, not flexible - Used for blades for tools and bridges.
- Stainless steel - mixed with chromium or nickel - corrosion resistant - used for cutlery.
Why are alloyed metals harder than pure metals?
Diffrent elements have diffrent sized atoms; when they are put into the rows of the pure metal they prevent the rows from sliding over eachother freely therfore making the metal harder.
Other Alloys You Need To Know
Bronze (used to make 1p and 2p coins) = Copper + Tin
Cupronickel (used to make silver coins) = Copper + Nickel
Gold (jewlery) = Zinc + Copper + silver + Palladium + Nickel + Gold
Aluminium is mixed with small amounts of other metals (you don't need to know what) to make it stronger.
That is EVERYTHING on metal finished!