© KCL. WCED. PENTECH. 2002

Metals from rocks 1

LIST the materials that these means of transport are made from.DECIDE on the one material used in the manufacture all three ?

Here are different ways of getting from A to B.

© KCL. WCED. PENTECH. 2002

Metals from rocks 2

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.

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strength of fibresstrength of block

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

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.

3Like all metals, iron has to be extracted from rocks in the Earth’s crust.

© KCL. WCED. PENTECH. 2002

Metals from rocks 4

Hot carbon dioxide gas, produced in the chemical reaction, is used to pre-heat incoming air.

Iron ore, limestone and coke in.

Pre-heated air in

Slag out

MoltenIronout

1700C

500C

200C

A chemical reaction takes place.The coke takes the oxygenfrom the iron oxide oreleaving molten iron.

The limestone mixeswith impuritiesto form waste slagwhich floats on the molten iron.

In a blast furnace iron oreis reduced to iron.

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

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 energyto 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.

The chemistry of extracting metals from ores

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.

Cyanide solution is added to crushed gold bearing ore to dissolve the gold and leave the unwanted rockbehind.

2.Excess Zinc metal is added to theCyanide and gold solution.The gold precipitates out and sinks to the bottom of the liquid.The zinc/cyanide solution is left behind.

4. 3.

Excess zinc metal is dissolvedinto the solution by adding sulphuric acid.

Only the gold metal is now left behind as a solid.

The heavy gold metalis filtered from the liquid.It is dried, then melted.The molten gold is pouredinto moulds to cool into rough gold plates for electrolytic refining.

USE a dictionary to help you with difficult words. DRAW a diagram to show the different types of atoms and moleculesthat 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 Price in Rand/tonne

Gold

Silver

Copper

Tin

Zinc

Chemical symbol

Cu

Au

Ag

Sn

Zn

DISPLAY the prices per kilogram in a graphical form.

CALCULATE the price for a kilogram of each metal.

DISCUSS possible reasons for why different metals cost different prices.

WRITE a report on why different metals are used for different purposes.

Aluminium Al

Lead Pb

13,000

16,000

110,000,000

4,400

1,700,000

41,000

7,500

Iron (steel) Fe 450

© 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 objectsit 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.