metal extraction slides

Extraction of metals (a) describe the ease of obtaining metals from their ores by relating the elements to their positions in the reactivity series

Recycling of metals (a) describe metal ores as a finite resource and hence the need to recycle metals, e.g. the recycling of iron

(b) discuss the social, economic and environmental issues of recycling metals

Iron (a) describe and explain the essential reactions in the extraction of iron using haematite, limestone and coke in the blast furnace

(b) describe the essential conditions for the corrosion (rusting) of iron as the presence of oxygen and water; prevention of rusting can be achieved by placing a barrier around the metal, e.g. painting; greasing; plastic coating

Metals from Rocks

•The substances (elements or compounds) that make up rocks are called minerals.

From Rocks to Metals• A metal ore (usually oxides, sulfides, chlorides

or carbonates) is a rock from which a useful metal is obtained.

• The process of getting metals from ores is called the extraction of metals.

Bauxite – an aluminium ore

Occurrence of Metals

• Metal oxides – metal + oxygen• Metal sulfides – metal + sulfur• Metal carbonates – metal + carbon +

oxygen

Some metal ores found in the Earth’s crust

Main minerals of metal ores

• Minerals are the elements or compounds that make up rocks.

• A metal ore is a rock containing a mineral from which a metal is extracted.

• Most minerals are the oxides, sulfides and carbonates of metals. For example, bauxite is an ore containing the compound aluminium oxide.

ore

metal compound separatedfrom bits of sand & rocks

purified

metal compound

metal

extracted metal chemically separatedfrom other elements

The Extraction of Metals

•The lower the position of a metal in the reactivity series, the easier it is to extract.

The reactivity series and the method of extracting metals

Extraction of the Least Reactive Metals• The least reactive metals are at the bottom of the

reactivity series. Some are found as free metals.• E.g. gold can be obtained by physical methods. The

rocks are collected and crushed to free the pieces of gold in them.

Rocks containing gold being extracted in a gold mine in Australia

• These metals occur as oxides and sulfides.

• The metal sulfides are heated in air to become metal oxides.

• The metal is then obtained by heating the oxides with carbon.

E.g.

Extraction of Less Reactive Metals

2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2ZnO(s) + C(s) Zn(s) +

CO(g)

Extraction of Very Reactive Metals

• Very reactive metals are difficult to extract.

• Most reactive metals are extracted by decomposing their compounds with electricity.

This is called electrolysis.

2KCl(l) 2K(l) + Cl2(g)

• The method used to extract a metal depends on the reactivity of the metal.

• Unreactive metals, such as gold, are often found as free (uncombined) elements.

• Less reactive metals are extracted by heating their oxides with carbon.

• Very reactive metals are extracted using electrolysis.

SummaryPotassium

SodiumCalcium

MagnesiumAluminium[Carbon]

ZincIronTin

LeadCopperSilverGold

More reactive metals

Less reactive metals

Unreactive metal

Electrolysis

Heating metal oxide with carbon

Physical methods

Heating the metal oxide

Extraction and Uses of MetalsExtraction and Uses of Metals

T H E M E F O U R : P E R I O D I C I T Y

C h a p t e r 13 Recycling of MetalsWhich Metals are Used Most?• Iron is used in the largest amounts,

followed by aluminium and copper.

Quantities of some metals produced



C h a p t e r 13• Only a limited amount of metal can be

mined from the Earth.



C h a p t e r 13

•One way of making metals last longer is to use other materials in their place.

•E.g. glass bottles for soft drinks are used instead of metal cans.

•Metals can be recycled.

Conserving Our Resources of Metals: Recycling



C h a p t e r 13Conserving Our Resources of Metals: Recycling

How aluminium cans are recycled



C h a p t e r 13• Conserves the Earth’s finite

resources of metals.• Saves cost of extracting new

metals.• Prevents land pollution caused by

the disposal of metals on landfills.

Benefits of Recycling

Recycling prevents unsightly car dumps

Recycled metal cans



C h a p t e r 13•Metals are only recycled if it is economical to do so.

•Can cause air pollution.•The cost of separating metals from waste can be high.

•Cost money to collect scrap metals.

•Difficult to persuade people to deposit used materials in recycling containers.

Some Problems with Recycling

Bins are provided for the collection of aluminium cans for recycling.



C h a p t e r 13• There are limited amounts of metal ores

in the Earth.• Recycling of metals has several

advantages. - It saves the limited amounts of metal

ores. - It saves the cost of extracting new

metals from ores. - It can help the environment by

preventing land pollution.• Recycling can cause air pollution and

cost money in transporting the scrap metals.

Extraction of Iron• Iron is mined from the

ground as iron ores.

• Haematite is one important ore.

• Iron is extracted from the oxide in a blast furnace.

• Iron ore, limestone and coke are fed in at the top of the furnace.

• Hot air is fed near the bottom of the furnace.



C h a p t e r 13Extraction of Iron

• The following reactions take place in the blast furnace:

• Coke reacts with oxygen to form carbon dioxide and heat.

• Carbon dioxide reacts with more coke to form carbon monoxide.

C(s) + O2(g) CO2(g)

CO2(g) + C(s) 2CO(g)



C h a p t e r 13• Carbon monoxide reacts with iron(III) oxide to produce molten iron.

• Limestone is decomposed by heat to produce calcium oxide and carbon dioxide.

Fe2O3(s) + 3CO(g) 2Fe(l) + 3CO2(g)

CaCO3(s) CaO(s) + CO2(g)

• What is the purpose of adding limestone into the blast furnace?

• To remove acidic impurities, like sand, SiO2 .



C h a p t e r 13• Impurities such as silicon dioxide reacts with calcium oxide to produce slag (calcium silicate).SiO2(s) + CaO(s) CaSiO3(l)

Acidic impurities,

sand

Extraction of iron

Hot waste gases such as carbon monoxide, carbon dioxide and nitrogen escape through the top of the furnace.

Molten iron is collected.

• Iron(III) oxide, coke, limestone and air are used in the extraction of iron.

• The iron is obtained by the reduction of iron(III) oxide with carbon monoxide.

• Most impurities are removed by reaction with calcium oxide (from limestone) to produce slag.

Exercise Time: The Conditions in the Blast Furnace

1. What is the role of coke in the blast furnace?

2. What is the role of limestone in the blast furnace?

3. Which ore of iron is commonly used in the blast furnace?

4. Why is it called a blast furnace?

5. What do we call the layer of impurities that forms at the base of the blast furnace above the liquid iron?

It acts as a reducing agent

Limestone helps to remove acidic impurities

Haematite

Because hot air is ‘blasted into the furnace’

Slag

Exercise:1. Which compound does haematite mainly consist of?

2. What is the chemical formula of this compound?

Iron (III) oxide

Fe2O3

Exercise1. Limestone is added to the blast furnace to remove acidic

impurities. What is the name and chemical formula of the compound that limestone mainly consists of?

2. In the blast furnace this compound undergoes thermal decomposition. Write a word equation for this reaction.

3. What is the chemical equation for this reaction?

4. Calcium oxide reacts with the impurity silicon dioxide. Write the chemical equation for this chemical reaction.

Calcium carbonate - CaCO3

Calcium carbonate calcium oxide + carbon dioxide

CaCO3 (s) CaO (s) + CO2 (g)

CaO (s) + SiO2 (s) CaSiO3 (l)

Questions :

1 a) Why is steel more suitable than iron in most uses ?

Iron is too malleable for most uses as the orderly layers of atoms can slide over each other easily.

Steel is an alloy consisting of different sized atoms, which disrupts the orderly arrangement of atoms, preventing the layers from sliding over each other easily. Hence, steel is harder and stronger for most uses.

b) Why is stainless steel popularly used for making cutlery ?

Stainless steel is corrosion resistant and does not rust.

1c) Why is recycling aluminium easier than recycling scrap iron?

Aluminium metal is very resistant to corrosion. This is because aluminium reacts with oxygen in the air to form a protective layer of aluminium oxide. Iron has poor resistance to corrosion and corrodes easily when exposed to air and water. It Hence it is difficult to recycle.



C h a p t e r 13Rusting•The corrosion of iron and steel is called rusting.

•The brown solid product formed during rusting is called rust. It is mainly iron(III) oxide, Fe2O3.



C h a p t e r 13 Conditions for RustingRusting : • Oxygen,• Water, and• Dissolved salt speeds up

rusting.



C h a p t e r 13Preventing Rusting• Surface Protection 1. Paint. e.g. street poles 2. Oil or grease e.g. machinery

Street poles are made of steel. These are protected from rusting by paint



C h a p t e r 13• Surface Protection

3. Plastic. e.g. metal clips4. Metal plating. e.g. food cans

Preventing Rusting

Steel clips covered with a layer of plastic.

Food cans are made of iron covered with a thin layer of tin. Most parts of the

motorcycle is plated with chromium.



C h a p t e r 13Ways to prevent rusting

Coating the object with a more reactive metal that corrodes in place

of iron. This is called “sacrificial protection”.

E.g. zinc (galvanized iron)



C h a p t e r 13Sacrificial Protection

•The sacrificial metal can be bolted directly on ship hull …..

… or be connected to the pipeline or oil rig by conducting cables.



C h a p t e r 13

•The more reactive metal corrodes in place of iron, hence iron is spared from rusting.

Sacrificial Protection

How this work.. ?



C h a p t e r 13

Advantages:

•Economical and most effective protection.

•Minimal maintenance is required.

Disadvantages:

•The sacrificial metal must be replaced before it all dissolves.

Sacrificial Protection



C h a p t e r 13

• Iron and steel rust in the presence of water and oxygen.

• Rusting can be prevented by coating the iron object with a layer of substance. This can be paint, oil, grease or another metal. It prevents air and water from reaching the iron.



C h a p t e r 13 Uses of Metals• The choice of one metal over another

depends on:- Its physical properties- Its chemical properties- Its cost

Aluminium used in trains



C h a p t e r 13 Uses of Metals



C h a p t e r 13

metal extraction slides

Education