ORES AND MINERALSORES AND MINERALS

Very reactive metalsVery reactive metals can only be extracted from their can only be extracted from their ores by electrolysis such as K, Na, Ca, Mg, and Al.ores by electrolysis such as K, Na, Ca, Mg, and Al.

Discussion on the extraction of the following:Discussion on the extraction of the following:

i. Aluminium from molten aluminium oxide (Bauxite) i. Aluminium from molten aluminium oxide (Bauxite)

ii. Sodium from molten sodium chloride (Halite).ii. Sodium from molten sodium chloride (Halite).

iii. Iron from iron (III) oxide Feiii. Iron from iron (III) oxide Fe22OO33, (Hematite)., (Hematite).

iv. Lead from Lead (II) sulphid , PbS (Galena).iv. Lead from Lead (II) sulphid , PbS (Galena).

v. Tin@Stanum from Tin (IV) Oxide SnOv. Tin@Stanum from Tin (IV) Oxide SnO22 (Cassiterite). (Cassiterite).

K

Na Very reactive metals

Ca Their ores require strong reduction which is

Mg done through electrolysis of molten ores

Al

Carbon

Zn Fairly reactive metals

Fe Their ores can be reduced by heating

Sn strongly with carbon

Pb

Hydrogen

Cu Their ores can easily be reduced by heating

Hg directly in air

Ag Less reactive metal

Au They exist as free metals in nature

EXTRACTION OF TIN/STANUMEXTRACTION OF TIN/STANUM

The main ore of tin is cassiterite which contains tin The main ore of tin is cassiterite which contains tin (IV) oxide, SnO(IV) oxide, SnO22. .

First First - Ore is first crushed, grounded and washed.- Ore is first crushed, grounded and washed.

SecondSecond - Flotation - mixing it with oil and water. In - Flotation - mixing it with oil and water. In this flotation method, the tin minerals, which are this flotation method, the tin minerals, which are less dense, are trapped in the floating form. The less dense, are trapped in the floating form. The impurities such as soil and sand which are denser, impurities such as soil and sand which are denser, sink to the bottom.sink to the bottom.

ThirdThird - Roasted in the air. This converts the - Roasted in the air. This converts the sulphide of tin to oxide. At the same time, sulphide of tin to oxide. At the same time, impurities such as sulphur and oil are burnt off.impurities such as sulphur and oil are burnt off.

FourthFourth - Reduction of tin (IV) oxide to tin by carbon - Reduction of tin (IV) oxide to tin by carbon monoxide and coke.monoxide and coke.

SnOSnO22 + 2CO → Sn + 2CO + 2CO → Sn + 2CO22

SnOSnO22 + 2C → Sn + 2CO + 2C → Sn + 2CO SnOSnO22 + C → Sn + CO + C → Sn + CO22

Last Last -The molten tin is drained off into moulds to -The molten tin is drained off into moulds to become blocks.become blocks.

RoastedRoasted( Reduction)Heated with

coke and limestone in blast furnace

( Reduction)Heated with

coke and limestone in blast furnace

Molten tin is drawn off and moulded

Molten tin is drawn off and moulded

Tin block

Cassiterite Crushed and washed

Crushed and washed

Flotation to concentrate the

ore

Flotation to concentrate the

ore

Flow-chart below summarises the extraction of tin / stanum

Properties of Stanum, SnProperties of Stanum, Sn

– Melting point 232Melting point 232ooCC– Boiling point 2603Boiling point 2603ooCC– Silvery in colourSilvery in colour– Highly ductile and malleable at Highly ductile and malleable at

temperature 100temperature 100ooCC

Uses of Stanum, Sn in daily lifeUses of Stanum, Sn in daily life

Widely used in alloy making:Widely used in alloy making:

i.i. Produce bronze as alloy (70% Cu + 30% Sn).Produce bronze as alloy (70% Cu + 30% Sn). ii.ii. Industrial processes as in the form of:Industrial processes as in the form of:

Tinplate, pewter (96% Sn + 3 % Cu and 1% Sb) and Tinplate, pewter (96% Sn + 3 % Cu and 1% Sb) and solders (70% Pb + 30% Sn)solders (70% Pb + 30% Sn)

iii. iii. In aerospace industry ( Stanum +Titanium ).In aerospace industry ( Stanum +Titanium ).

iv. iv. Insecticides.Insecticides.

EXTRACTION OF ALUMINIUM

Aluminium is extracted from its ore (bauxite) which Aluminium is extracted from its ore (bauxite) which contains aluminium oxide Alcontains aluminium oxide Al22OO33 . 2H . 2H22OONote:Aluminium not from AlClNote:Aluminium not from AlCl33 because AlCl because AlCl33 does not melt when heated. does not melt when heated.

Aluminium oxide is mixed with cryolite, NaAluminium oxide is mixed with cryolite, Na33AlFAlF66

to lower the melting point of aluminium oxide from to lower the melting point of aluminium oxide from 20452045ooC to about 900C to about 900ooCC. .

4000 A current is used to keep the temperature of 4000 A current is used to keep the temperature of the electrolysis cell at 900the electrolysis cell at 900ooC.C.

Block of carbon act as anodesBlock of carbon act as anodesCarbon lining act as cathode.Carbon lining act as cathode.

Cathode: AlAl3+3+ + 3e → Al + 3e → AlAnode:

2O2O2-2- → O → O22 + 4e + 4e--

The overall chemical reaction is:The overall chemical reaction is: 2Al2Al22OO33 → 4Al + 3O → 4Al + 3O22

The oxygen liberated at the anode will react The oxygen liberated at the anode will react with the carbon electrode to produce carbon with the carbon electrode to produce carbon dioxide gas.dioxide gas.The anode is corroded slowly and must be The anode is corroded slowly and must be replaced form time to time.replaced form time to time.

Physical Properties of AluminiumPhysical Properties of Aluminium

1) Is strong.1) Is strong.2) 2) malleable . .3) Low 3) Low density..4) Resistant to 4) Resistant to corrosion because the presence because the presence

of an impervious oxide layer on the surface ofof an impervious oxide layer on the surface of aluminium.aluminium.

5) G5) Good conductor of heat and electricity. of heat and electricity.6) Can be polished to give a highly reflective6) Can be polished to give a highly reflective

surface.surface.

Chemical properties of aluminiumChemical properties of aluminium

1) Reaction with non-metallic elements when 1) Reaction with non-metallic elements when heated.heated.

4Al + 3O4Al + 3O22 2Al2Al22OO33

2Al + 3S 2Al + 3S AlAl22SS33

2Al + N2Al + N22 2AlN2AlN

4Al + 3C 4Al + 3C AlAl44CC33

2Al + 3Cl2Al + 3Cl22 AlAl22ClCl66

Chemical properties of AluminiumChemical properties of Aluminium

2) React with hydrochloric acid and 2) React with hydrochloric acid and sulphuric acidsulphuric acid

2Al + 6HCl → 2AlCl2Al + 6HCl → 2AlCl33 + 3H + 3H22

However, with hot dilute or concentrated sulphuric However, with hot dilute or concentrated sulphuric (VI) acid, sulphur dioxide gas is liberated(VI) acid, sulphur dioxide gas is liberated

2Al + 6H2Al + 6H22SOSO44 → Al → Al22(SO(SO44))33 + 3SO + 3SO22 + 6H + 6H22OO

Chemical properties of aluminiumChemical properties of aluminium

3) Reaction with alkalis3) Reaction with alkalis

The reaction is highly exothermic.The reaction is highly exothermic.

2Al + 2NaOH + 6H2Al + 2NaOH + 6H22O → 2NaAl(OH) + 3HO → 2NaAl(OH) + 3H22

Uses of AluminiumUses of Aluminium

Shiny metal – Used as jewelley.Shiny metal – Used as jewelley.

Low density - Used to make aeroplanes and Low density - Used to make aeroplanes and trains.trains.

Non- toxic –Used in a drink cans and roofing Non- toxic –Used in a drink cans and roofing materials materials

EXTRACTION OF IRON

Ores:hematite, Fe2O3 and magnetite,

Fe3O4.

First - remove the impurities.First - remove the impurities.

Then, concentrated ores are reduced by carbon in Then, concentrated ores are reduced by carbon in the form of the form of cokecoke in a very large and hot furnace in a very large and hot furnace called called blast furnaceblast furnace. Its temperature can reach up . Its temperature can reach up 20002000ooC.C.

A A small charge small charge ( consists of concentrated iron ( consists of concentrated iron ores, coke and limestone )is introduced ores, coke and limestone )is introduced from the from the top of the blast furnace top of the blast furnace at intervals of 10 to 15 at intervals of 10 to 15 minutes.minutes.

Blast of extremely hot air are pumped through the furnace via the bottom. The oxygen in the hot air reacts with coke to form

carbon dioxide . C + O2 → CO2

Blast of extremely hot air are pumped through the furnace via the bottom. The oxygen in the hot air reacts with coke to form

carbon dioxide . C + O2 → CO2

Excess carbon reacts with carbon dioxide producing carbon monoxide ( the main reducing agent) in the furnace.

C + CO2 → 2CO

Excess carbon reacts with carbon dioxide producing carbon monoxide ( the main reducing agent) in the furnace.

C + CO2 → 2CO

Carbon monoxide and carbon reduce the iron oxides to iron.

Fe2O3 + 3CO → 2Fe + 3CO2

2Fe2O3 + 3C → 4 Fe + 3CO2

Fe3O4 + 4CO → 3Fe + 4CO2

Fe3O4 + 2C → 3Fe + 2CO2

Carbon monoxide and carbon reduce the iron oxides to iron.

Fe2O3 + 3CO → 2Fe + 3CO2

2Fe2O3 + 3C → 4 Fe + 3CO2

Fe3O4 + 4CO → 3Fe + 4CO2

Fe3O4 + 2C → 3Fe + 2CO2

The following flow chart outlines the reduction of the iron ores The following flow chart outlines the reduction of the iron ores

The molten iron is collected at the bottom of the The molten iron is collected at the bottom of the furnace. It is drained off periodically into moulds furnace. It is drained off periodically into moulds and is allowed to cool. The product known as cast and is allowed to cool. The product known as cast iron.iron.

At the same time, the At the same time, the limestone decomposes tolimestone decomposes to..

CaCOCaCO33 → CaO + CO → CaO + CO22

The The calcium oxide then reacts with the impurities calcium oxide then reacts with the impurities in the oresin the ores, which consist mostly of sand, SiO, which consist mostly of sand, SiO22 to to form calcium silicate, CaSiOform calcium silicate, CaSiO33 or or slagslag..

CaO + SiOCaO + SiO22 → CaSiO → CaSiO33(l)- slag(l)- slag

Properties and Uses of IronProperties and Uses of Iron

Cast iron is very brittle (it cracks easily) Cast iron is very brittle (it cracks easily) butbut it has a it has a greater resistance to corrosion than either pure iron greater resistance to corrosion than either pure iron or or steel..

Cast iron is used for manhole covers on roads and Cast iron is used for manhole covers on roads and pavements and as engine blocks for pavements and as engine blocks for petrol and diesel and diesel engines.engines.

Pure iron is called wrought iron. Wrought iron is Pure iron is called wrought iron. Wrought iron is malleable and is mainly used in ornamental work for malleable and is mainly used in ornamental work for gates.gates.

React as catalyst in the Haber Process.React as catalyst in the Haber Process.

EXTRACTION OF LEAD, Pb

Lead Ores - Galena, PbS.Lead Ores - Galena, PbS.

Process: (heating & electrolysis)Process: (heating & electrolysis)

FirstFirst - Lead bromide must be heated until - Lead bromide must be heated until it is molten before it will conduct electricity.it is molten before it will conduct electricity.

SecondSecond - Electrolysis separates the - Electrolysis separates the molten ionic compound into its elements molten ionic compound into its elements

Cathode:Cathode: PbPb2+2+  +  2e-  →     Pb  +  2e-  →     Pb

Anode:Anode:

2Br2Br--   →     Br   →     Br2 2 + 2e+ 2e

The overall reaction isThe overall reaction is

PbBrPbBr22(l)      →     Pb(s)  +   Br(l)      →     Pb(s)  +   Br22(g)(g)

Properties of Lead, PbProperties of Lead, Pb

– Melting point 327.4Melting point 327.4ooCC– boiling point 1750boiling point 1750ooCC– Soft metal.Soft metal.– Easily Easily malleabilitymalleability or can be shaped. or can be shaped.– Grey in colour.Grey in colour.– Resistance to corrosion.Resistance to corrosion.

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