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Metals from rocks 1
Here are different ways of getting from A to B.
LIST the materials that these means of transport are made from.
DECIDE on the one material used in the manufacture all three ?
© KCL. WCED. PENTECH. 2002
Metals from rocks 2
3
strength of fibres
strength of block
2
1
silica glass
iron
0
graphite
Relative strengths of materials
Iron is used to make all sorts of objects, including cars, trains and bicycles.
One of the advantages of iron is its strength.
Scientists often measure the strength of both thin fibres and large blocks.
DESCRIBE what the graph shows.
DISCUSS what other reasons may explain the wide use of iron.
From your own experience, DESCRIBE some of the disadvantages of iron.
© KCL. WCED. PENTECH. 2002
Metals from rocks 3
Like all metals,
iron has to be extracted
from rocks in the Earth’s crust.
Processing rocks
• Firstly, the rocks have to be removed from the Earth. This is done through mining.
Open cast mines involve taking the rocks from the top of the ground.
In quarries the rocks are blasted out.
In deep mines the miners go underground to dig out the rocks.
• Then the rocks are crushed into small pieces.
• Quite often the pieces of rock are mixed with water and a foaming agent.
The unwanted earthy material is carried away in the froth of the foam.
The metal workers are then able to separate the metal carrying ore, because it sinks.
• Lastly the washed, crushed ore is then roasted
to prepare it for the extraction of the metal.
DRAW a series of linked diagrams to show the stages of processing.
© KCL. WCED. PENTECH. 2002
Metals from rocks 4
In a blast furnace iron ore
is reduced to iron.
Iron ore, limestone
and coke in.
A chemical reaction takes place.
The coke takes the oxygen
from the iron oxide ore
leaving molten iron.
The limestone mixes
with impurities
to form waste slag
which floats
on the molten iron.
Hot carbon dioxide gas,
produced in the chemical reaction,
is used to pre-heat incoming air.
200C
500C
1700C
Pre-heated
air in
Molten
Iron
out
Slag
out
Look carefully at the diagram of the blast furnace. Use the diagram to help you.
WRITE OUT how iron oxide, in iron ore, is turned into iron in the blast furnace.
© KCL. WCED. PENTECH. 2002
Metals from rocks 5
The chemistry
of extracting metals
from ores
Lecture notes
The extraction of iron from its ores illustrates a general process of metal extraction.
Firstly, the iron ore is mixed with coke.
The coke is mostly the element carbon.
The iron ore contains the two elements, iron and oxygen.
By heating the coke and ore together, the atoms of oxygen gain enough energy
to separate from the iron atoms and combine with the carbon atoms.
The combination of oxygen and carbon atoms gives carbon dioxide.
This is a gas. The hot gas escapes and leaves the iron atoms behind.
The iron atoms, as molten iron run, to the bottom of the blast furnace.
Chemists say the iron ore has been reduced from iron oxide to the metal iron.
At the same time, the carbon in the coke has been oxidised to carbon dioxide.
Use the lecture notes to DRAW diagrams to show the chemical reactions.
Use atoms to show what happens chemically.
Label the processes of reduction and oxidation.
© KCL. WCED. PENTECH. 2002
Metals from rocks 6
Gold metal is also extracted from the rocks of the Earth.
Large quantities of gold bearing rock are mined from deep mines.
Again, the rocks are crushed to make extraction possible.
1.
2.
Excess Zinc metal is added to the
Cyanide and gold solution.
The gold precipitates out and
sinks to the bottom of the liquid.
The zinc/cyanide solution
is left behind.
Cyanide solution is added to
crushed gold bearing ore
to dissolve the gold
and leave the unwanted rock
behind.
The heavy gold metal
is filtered from the liquid.
It is dried, then melted.
The molten gold is poured
into moulds to cool into
rough gold plates for
electrolytic refining.
4.
3.
Excess zinc metal is dissolved
into the solution by adding
sulphuric acid.
Only the gold metal
is now left behind as a solid.
USE a dictionary to help you with difficult words.
DRAW a diagram to show the different types of atoms and molecules
that are present at each stage of the process of extraction of gold from its ore.
© KCL. WCED. PENTECH. 2002
Metals from rocks 7
Here are some prices for different metals on the Johannesburg Stock Exchange.
( A metric tonne is one thousand kilograms.)
Metal
Chemical symbol
Price in Rand/tonne
Aluminium
Al
13,000
Copper
Cu
16,000
Gold
Au
110,000,000
Iron (steel)
Fe
450
Lead
Pb
4,400
Silver
Ag
1,700,000
Tin
Sn
41,000
Zinc
Zn
7,500
CALCULATE the price for a kilogram of each metal.
DISPLAY the prices per kilogram in a graphical form.
DISCUSS possible reasons for why different metals cost different prices.
WRITE a report on why different metals are used for different purposes.
© KCL. WCED. PENTECH. 2002
Metals from rocks 8
The market is over. People are packing up their belongings.
They will return to their homes.
They will leave a lot of rubbish behind.
Even though the rubbish may be many different objects
it is made from only a few materials.
LIST the different materials that make up our rubbish.
One material in rubbish is iron. It is in cans, pins, dented bowls, blunt knives,
broken buckles, screws, fixtures and fittings.
Use you knowledge of the extraction of metals from the Earth
to EXPLAIN why we should try to re-cycle iron.
© KCL. WCED. PENTECH. 2002